Airgun Accuracy

Only accurate airguns are interesting!

Feinwerkbau P70 conversion to 16 Joule / 12 fpe for Field Target

 

 FWBlogo

On this page I will report on the conversion of an Feinwerkbau P70 rifle from 7,5 to a 16 Joule/12 footpound field target rifle.  The story will follow the process so updates will be added regularly.

I got interested in the Feinwerkbau (FWB) rifles for field target use by many positive posts about these rifles, their excellent accuracy barrels, and the good possibilities for conversion. A lot of info is posted by “Jason Goldsmith / JG66 / Adminmaster”, Jon and MarcKA on the www.Pimpmyairgun.com forum. Maestro from Maestro Design also has published a lot of info about the Feinwerkbau P70 field target rifles. See www.maestro-design.co.uk/portfolio/feinwerkbau for his dedicated Feinwerkbau P70 parts.

In my younger years I have spent many years with the Feinwerkbau 300 and later the Feinwerkbau 600 model for 10 meter ISSF competition. But when the pre-charged pneumatics with aluminum stocks came in fashion I switched to the Walther LG300. The aluminium stocked Feinwerkbau P70 felt very heavy and unbalanced to me at the time.  And still does. But the laminated wood stock from the FWB 600 always fitted me very well. So when I noticed an used Feinwerkbau P70 with a wooden stock at a local dealer for a very good price I could not resist and had to have this Feinwerkbau P70. It is a 10 meter 7,5 Joule version so it needs some work to get it ready for field target use.

Feinwerkbau P70, 10meter ISSF version dated 1998

The starting point for the conversion: Feinwerkbau P70, 10meter ISSF version dated 1998

My first step was to got to the Feinwerkbau website to compare the drawings from the 7,5 Joule P70 and the 15,5 Joule P70 Field Target rifle. I copied the parts lists from both into a spreadsheet and after some sorting looked for the part numbers that are different between the P70Alu and P70FT.

Table 1. Part numbers that are different between the 7.5 and 15.5 Joule version of the Feinwerkbau P70

Artikel-Nr. Article-No. Bezeichnung Description Preisgruppe Price group Remark Preis Kimla (eur) 16-9-2014
3.2.000.341 Absorber, links, montiert Absorber, left, mounted D3 P70ALU 118.97
1746.3 Abzug mit Absorber, vollständig Trigger complete with absorber U4 P70ALU
3.2.034.3 Abzug, vollständig, Field Target Trigger, complete, Field Target T4 P70FT 621.35
1746.302.1 Abzugträger Trigger housing O3 P70ALU 132.78
3.2.008.302 Abzugträger Trigger housing V3 P70FT 202.06
1746.301.2 Abzugträger, montiert Trigger housing, mounted T3 P70ALU 198.06
3.2.008.301 Abzugträger, montiert Trigger housing, mounted E4 P70FT 384.67
3.2.008.305 Achse Axle B1 P70FT 1.25
3.2.008.306 Achse Axle B1 P70FT 1.25
1780.363.1 Achse Axle J1 P70ALU 3.77
1840.115.1 Achse Axle J1 P70ALU 3.77
3.2.004.301 Deckplatte (Absorber) Cover plate U1 P70FT 11.18
1746.306.3 Druckfeder Compression spring C1 P70ALU 1.47
4.9.0203 Druckfeder (schlagbolzen) Compression spring (for firing pin) J1 P70FT 3.77
1746.203.2 Druckminderer, montiert Pressure reducer, mounted T3 P70ALU 174.73
3.2.034.203 Druckminderer, montiert Pressure reducer housing, mounted T3 P70FT 174.73
3.2.008.304 Klappe Flap T2 P70FT 37.76
1746.362.1 Klappe (Rechtssystem) Flap (right system) M2 P70ALU 25.97
1746.307.1 Lagerschraube Firing pin spring screw A2 P70ALU 16.05
3.2.034.307 Lagerschraube Firing pin spring screw N1 P70FT 5.70
1780.209.1 Lauf Barrel U3 P70ALU 187.26
3.2.034.209 Lauf, Field Target Barrel, Field Target V3 P70FT 202.06
1750.207.1 Laufmantel Barrel sleeve X2 P70ALU 56.07
3.2.018.108 Laufmantel Barrel sleeve H3 P70FT 90.77
3.2.034.113 Laufgewicht, vollständig, Field Target Barrel weight, complete, Field Target E3 P70FT 77.04
3.2.000.101 Laufgewicht, vorne, vollständig Barrel weight, front, complete B3 P70ALU 64.59
4.9.0011 O-Ring 25,2 x 3,0 (Fur Zwischenring 15/20J) O-Ring 25,2 x 3,0 F1 P70FT 1.8
4.9.0001 O-Ring 4,0×1 (Abdekplatte Absorber) O-Ring 4,0 x 1,0 F1 P70FT 1.8
1798.305.1 Schlagbolzen Firing pin T2 P70ALU 37.76
3.2.034.305 Schlagbolzen Firing pin P2 P70FT 30.57
6.2093.025 Tellerfeder 16x 8,2 Disc spring 16×8,2 A1 P70ALU 0.91
1798.204.1 Träger Barrel support N3 P70ALU 125.85
3.2.034.108 Träger Barrel support O3 P70FT 132.78
3.2.034.215 Zwischenring, 15 Joule Intermediate plate, 15J V2 P70FT 44.16
3.2.036.220 Zwischenring, 20,4 Joule Intermediate plate, 20,4J V2 P70FT 44.16
1780.106.9 Zylinderschraube (Deckplatte Absorber) Cylinder head screw A1 P70FT 0.91

The table here shows all the part numbers that differ between the P70 and the P70FT rifle.  I added some parts that are needed extra such as the belleville washers (Tellerfeder/Disc spring) of which the P70FT needs 12 instead of 10. To mount the Intermediate plate 15J or 20,4J , (the 15 Joule or 20 Joule spacer for the pressure regulator) you need an extra o-ring 25,2 x 3,0 so that is also in the list.

This list is quite long but not all the parts are needed for a conversion. The Absorber for instance is a difference but only mounted on the P70. The P70FT does not need it. The barrel can also stay in place. And you do not need the Field Target Barrel weight. The Pressure reducer can be converted with two extra belleville washers.

If we select the P70 Field Target rifle parts the list for parts I think I need to order is:

Table 2. Parts that are most probably needed for a conversion from 7.5 to 15,5 Joule

Artikel-Nr. Article-No. Bezeichnung Description Preisgruppe Price group Remark Preis Kimla (eur) 16-9-2014
3.2.008.305 Achse Axle B1 P70FT 1.25
3.2.008.306 Achse Axle B1 P70FT 1.25
4.9.0203 Druckfeder (schlagbolzen) Compression spring (for firing pin) J1 P70FT 3.77
3.2.008.304 Klappe Flap T2 P70FT 37.76
3.2.034.307 Lagerschraube Firing pin spring screw N1 P70FT 5.70
4.9.0011 O-Ring 25,2 x 3,0 (Fur Zwischenring 15/20J) O-Ring 25,2 x 3,0 F1 P70FT 1.8
3.2.034.305 Schlagbolzen Firing pin P2 P70FT 30.57
3.2.036.220 Zwischenring, 20,4 Joule Intermediate plate, 20,4J V2 P70FT 44.16
1780.106.9 Zylinderschraube (Deckplatte Absorber) Cylinder head screw A1 P70FT 0.91
4.9.0001 O-Ring 4,0×1 (Abdekplatte Absorber) O-Ring 4,0 x 1,0 F1 P70FT 1.8
3.2.004.301 Deckplatte (Absorber) Cover plate U1 P70FT 11.18
6.2093.025 Tellerfeder 16x 8,2 Disc spring 16×8,2 A1 P70ALU 0.91
1754.334.1 Sichtleiste Plastic latch  P1  P70FT  5.90

The two “Achse” / Axles are needed when you want to mount a handle at the side of the loading lever flap (Sichtleiste / Plastic latch). These axles are longer so they can go through the new handle.

The “Druckfeder”/ Firing spring is stronger for the P70 FT to open the firing valve against the  higher air pressure used in the P70 FT. Also probably to open it further and longer to get more air behind the pellet.

The “Klappe” / Flap is the lever that you need to push to close the breech. The FT version is shorter so it does not interfere with the scope or scope mount.

The “Lagerschraube” is the screw that keeps the striker/hammer spring in place. It is much shorter to accommodate the longer hammer spring.

The “O-ring 25,2 x 3,0” is the seal between the pressure regulator and the barrel support. To fit the “intermediate plate 20,4J” one extra is needed.

The “Schlagbolzen”/ Firing pin for the P70 FT is heavier to open the valve against the higher reg pressure and open it more and longer.

The “Zwischenring 20,4Joule” is the spacer that goes between the reg housing and the barrel support. It creates a larger chamber for the regulated air. More air can be delivered to the pellet.

The next three parts (Zylinderschraube, O-Ring 4,0×1, Deckplatte) are needed when the Absorber is removed from the slider that closes the breech. These parts close the port in the slider where the air is going through into the Absorber.

The “Tellerfeder 16 x 8,2” are the Belleville springs inside the pressure regulator. The P70 FT has 11 or 12 of these compared to 10 in the 7,5J P70. There seems to be no agreement on the number of extra springs on the internet. This might be due to fact that there are two slightly different versions of the P70 regulator. The 7,5J reg that is normally set to 80 bar (at least om my rifle it was) can also reach 90 to 95 bar which might be sufficient for 16J.

The “Sichtleiste”/ Plastic latch is the small handle on the side of the breech closing lever (Klappe).

The “Träger”is the barrel support. On the P70 FT it has a larger opening where the air passes from regulator to valveblock. As this is a very expensive part it might be wiser to modify the original by enlarging the hole.

Total cost for the above parts is 148 Euro. Is is probably possible to shorten the breech slider flap instead of ordering a new one. This would reduce the costs for a conversion to 110 Euro. [all prices dated 16th of September 2014 and from web sources]

Feinwerkbau P70 cut open view 1

Feinwerkbau P70 cut open view 1

Feinwerkbau P70 cut open view 2

Feinwerkbau P70 cut open view 2. Red part is the pressure regulator, Green is the Barrel support, Yellow the valve block

Feinwerkbau p70 cut open view 3

Feinwerkbau p70 cut open view 3. Showing the hammer/striker with short spring and long screw (black)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The main challenge that remains after ordering the necessary Feinwerkbau parts is the mounting of the scope.

The original 10 meter FWB P70 has no reliable scope rail. There is a dovetail on the rear of the breechblock. But it is known that mounting a scope there will cause problems with point of impact (POI) shift. FWB also has its own specs for this scope rail. It is not the standard 11mm dovetail seen on many airguns. Fitting a scope mount there might cause the scope being off line with the barrel center line in the left-right plane.

The large aluminum triggerblock  of the P70 is connected to the aluminum barrel holder (Träger in German) by two screws only. And the steel valve block is screwed on the barrel holder in between the two. The regulator housing is bolted to the barrel support with 4 bolts. All these parts bolted together are too flexible to keep a scope mounted on the breechblock dovetail in line with the barrel.  Temperature, humidity and pressure on the stock or system move this whole system and change the Point Of Impact (POI).

Feinwerkbau P70 system main parts IMAG2133

Feinwerkbau P70 system 1. The central barrel holder that is fixed in the stock with 3 bolts and where the regulator (left), valveblock (middle) and triggerblock (right) are bolted on. (the striker and spring are missing in these pictures)

Feinwerkbau P70 system 3.

Feinwerkbau P70 system 2.

Feinwerkbau P70 system 2.

Feinwerkbau P70 system 3.

General consensus seems to be to mount the scope on the barrel sleeve to prevent POI shift. The P70Field Target has a dovetail on the barrel sleeve for scope mounting.  So it seems Feinwerkbau also advises to mount a scope on the barrel. As my 10m rifle has no such dovetails on the barrel sleeve something has to be thought out to properly mount a scope.

I could mill dovetails into the barrel sleeve or make a scope mount that clamps around the barrelsleeve. The last option is currently the one I favour most. It has the lowest risk of scrapping something costly (eg. the barrelsleeve with the barrel glued inside it).


The Feinwerkbau conversion parts have arrived

14 th of October 2014

The FWB parts I ordered last week from Sportwaffen Hasselhorst in Germany have arrived.

The strikers compared

On my laboratory scale I weighed the strikers/hammers. The P70FT striker is almost 15 grams heavier compared to the 10 meter (7,5 Joule) version (34.81 vs. 19.83 gram). That’s a 75% increase in weight.

The Striker Springs compared

The spring for the P70FT has a 1.90mm wire diameter compared to a 1.60mm for the 7,5J P70. This may seem a small 0.30mm difference but it makes a big difference in the force of the spring. Calculations shows that the spring force more than doubles (4.2 to 9.6 N/mm) with this 0.30 mm increase in wire diameter (for the same spring length, spring diameter and no. of coils). The formula to calculate the force of a spring is:

R = 1000 x WD4 ÷ ( CDX AC )

Were:

R: The force of the spring in Newton/millimeter. So R is the force in Newton needed to compress the spring 1millimeter. 1 Newton is 0,1 kilogram.

1000: The factor to incorparate the quality of the spring steel. (1000 assumes a decent quality steel).

WD: wire diameter (mm) to the fourth power

CD: coil diameter (mm) to the third power. (this is the coil diameter from the center of the wires. Can be found by subtracting the wire diameter from the outer coil diameter

AC: number of active coils. (can be found by counting the number of full gaps between the coils)

When we fill the parameters for the 8mm diameter, 1,6 mm wire Feinwerkbau 7.5 Joule striker spring: R = 1000 x WD 1.60 4 ÷ ( CD 6.4 X AC 6 ) = 4.17 N/mm

When we fill the parameters for the 8mm diameter, 1,9 mm wire Feinwerkbau FT 16 Joule striker spring: R = 1000 x WD 1.90 4 ÷ ( CD 6.1 X AC 6 ) = 9.57 N/mm

You see that the spring force increases with the Wire Diameter to the fourth power. This explains why the 0,30mm increase in wire diameter of the P70FT increases the force of this spring by a factor 2.3 or 230 percent.

 P70 (top) and P70FT Setscrew, Spring and Strikers compared

P70 (top) and P70FT Setscrew, Spring and Strikers compared.


The FWB P70 is on 15,4 Joule.

30th of October 2014 . Let me start to say that this FWB P70 took some more time to convert to a field target rifle than a Walther.

I first removed the strikerspring setscrew, strikerspring and striker and cleaned the triggerblock that had accumulated some dirt and hardened grease over the years with the previous owner.

I cleaned the oil away from the new FT striker and installed the new striker and spring. I’m starting with a dry, no oil or grease, striker. Oil or grease will change viscosity with temperature and this will affect the consistency of the muzzle velocity.

To install the short latch that is needed to clear the scope I removed the circlips from both pins. The rear pin that sits in the triggerblock needs to be driven out while supporting the side of the old long type latch. Same for installing it back with the short latch in place. The front pin just slides out.

I removed the Absorber and screwed on the new cover plate with an new screw. The old o-ring stayed in place.  Safety Warning: When you are going to increase the power of your own P70, or any other FWB rifle with an Absorber, make sure you remove the Absorber for safety reasons. The Absorber tube contains a weight that is pushed backwards by the air that also propels the pellet forward. When the amount and pressure of the air are increased the Absorber will move backwards with much greater speed (in the direction of your face!). There is a chance that the pin that stops the Absorber weight may not withstand this increased power and fails at some point. The Absorber weight will then be shot into your face! Be careful! Later on I plan to experiment more with the Absorber to see if it can be modified and used safely at a 16 Joule / 12FPE P70.

I took off the pressure regulator and put the 20 joule spacer on the Träger/barrel holder with a new o-ring in between. Then I noticed the four original M5 bolts that hold the regulator were too short. So I measured the thickness of the 20J spacer plate and went looking and found some M5 x 30mm bolt to replace the originals.

I screwed the regulator back on and tested for velocity. This gave me 185 m/s or 9.2 Joule

I started to adjust the striker spring preload and quickly noticed that the adjuster screw has a very coarse threading (M12x1.75). A little turn can give a big change in velocity. And it is easy to overdo it and fully compress the spring. So I backed it off again and got to a max of 190 m/s. Not 16J or 12 FPE in a long way. But this was what I expected with the standard setting of the pressure regulator. Factory setting for the P70 is 80 to 85 bar output pressure. The factory setting for the P70 FT on 16J is 100 Bar

I made a tool from some 3mm brass strip to adjust the regulator. The setscrew  on the reg is from brass and could easily be damaged with a steel tool.

P70 regulator adjustment screw

P70 regulator adjustment screw

 

This regulator set screw also has a coarse threading like the striker spring setscrew. So a little turning does a lot to the output pressure. I read on Pimpmyairgun.com that the factory setting for the 16 joule P70 regulator is 100 bar (and 110 for the 21 joule). Velocity went from 190 to max 220 m/s (0,54 gram / 8,3 grain JSB Exact). And when I gave another small turn it stayed at 220 and another one reduced the velocity to 200. So it seemed 220m/s was the max velocity with this setup. Clockwise will increase the output pressure.

When I compared the spare parts lists of the P70 and the P70FT I already noticed that the ” Trager” or ” Barrel Support” is different for the FT version.  As this is an expensive 132 euro part I decided not to buy this. From the internet I learned that the difference was a 1 or 2mm larger transfer port in this Trager. I measured the port in my Trager and it was just over 3.5mm. I decided to enlarge the transfer port with 1.50mm (the average of the mentioned 1 and 2 mm) to a port of 5.0mm.

I put the Trager with barrel and all in the mill and took a 5mm end mill to do the job. I put the Trager under an angle in the vice to make sure I kept the seat for the valve return spring intact. A larger port central to the original 3.5mm port will reduce the seating surface for the spring. To prevent this I milled under an angle and also moved the new port away from the spring seat. It took quite some measuring, sketches and thinking to arrive at the right position for the end mill to start. (NB: Do Not Try this At Home: Be careful when you want to do this yourself: A normal drill bit will NOT do the job. It will wander away when drilling under an angle! Remember this is an 132 euro / $165 part.)

Milling a new port in the Barrel support.

Milling a new port in the Barrel support.

New angled 5mm port ready

New 5mm port ready

 

The new port was chamfered to get a smoother airflow. After this operation the parts were assembled and tested for velocity: 220 m/s. I cranked up the reg some more…. and the velocity went down. What now? I’m not at 16 J yet.

I had read on the internet (yes, pimpmyairgun again, a very informative site) that the FT regulator has 12 belleville springs compared to 10 in the 7.5J version. I had ordered new belleville springs so my thoughts now were to add some to the reg. As this makes it necessary to open the reg it would mean I would loose the current pressure setting. I measured the height that the brass adjuster screw protrudes above the reg housing to be able to replicate that later. Adding extra springs is a piece of cake. Unscrew the brass setscrew completely. Drop in 2 disc springs and close again.

And it did NOT work. Why not? After assembly I was of course completely lost about the reg output pressure. I tested for velocity. Adjusted reg and strikerspring but never got it back to 220 m/s. I got to a max 215 m/s.

So I need to to make a regulator tester to know how much output pressure the reg was delivering.

Feinwerkbau P70 regulator tester.

Feinwerkbau P70 regulator tester.

 

I put some 25mm thick and 50 x 50 aluminum in the lathe and turned until the face side measured the same as the protrusion on the Barrel Support that holds the regulator. Then measured the positions and dimensions for the bolts and for the manometer. Drilled and tapped for a 1/4G hole for the manometer. Looked a long time for a good seal for the manometer and after an evening of work I had my Feinwerkbau regulator tester. I have seen an original Feinwerkbau made reg tester in real life and this uses only two bolts to hold the reg in place. Saved me measuring out and drilling 2 holes.

I screwed on the P70 reg on and screwed the air cilinder on that: 125 Bar. Oops that is a bit high for 16J. Now I knew why the velocity was low: the high pressure puts a large force on the firing valve which makes it difficult to open and faster to close.

I reduced the reg pressure to 100 bar. But then the brass set screw on the reg was sticking too much out of the reg body to my liking. The 2 extra bellevilles make the spring package too large. I removed the 2 extra bellevilles and tested again to set the reg to 100 bar. This time it worked. The set screw engages with all threads and sits nicely. At about the protrusion as the original 80 bar setting.

Velocity testing showed 234 m/s. And a very small tweak on the striker spring gave me 239 m/s. Good enough for me: 15,4 Joule. The extreme spread over 10 shots was 1.0 m/s. Nice.

So I followed a winding road to my 16 Joule destination. Would have been better to convert the Barrel support transferport to 5mm first and adjust the regulator only after that. And without adding the extra belleville springs setting the regulator would have been a more straightforward job. The marking and a caliper showed the brass setscrew needed just under 90 degree turning to arrive at 15,6 Joule. No extra bellevilles needed.

Next thing is to make a scope mount that fits on the barrel.


 Scope mounting

Mounting the scope on a 10 meter version Feinwerkbau P70 is not easy. For good results the scope needs to be mounted on the barrel. The P70 field target rifle has  dovetail grooves milled into the barrel shroud to put the scope mounts onto. The 10 meter version does not have this.

I solved the problem in a quick and maybe not too good looking way at first. This is to be able to test the rifle for accuracy first before investing time and money in a better mechanical and better looking option.

I took a MEC Tube sight line extender that I had lying around. This is just a aluminum tube that fits over the barrel and has dovetail grooves on top. I cut a 32mm long piece off to fit on the barrel above the regulator. I milled the bottom of the tube to 0.95mm thickness to clear the regulator. The cocking lever sits tight against the barrel which is why I needed  to cut the tube in two parts. Between cocking lever and barrel there is no space for the tube.

The second part of the MEC tube was also milled at the bottom to clear the air cartridge. Thickness here was 2 mm. The tube is normally fixed to the barrel by 3 short grub screws at the bottom. Because I milled the bottom and need the clearance there I drilled and tapped the top of both the tube parts to place the screws there.

The 2 parts of the MEC tube fit nicely on the barrel. On the dovetail of both the the tube parts I fitted  a B-Square width adjustable riser block to overcome the difference between the 12mm dovetail on the MEC tube and the 11m scope rail (FWB also uses 12mm rails on the trigger block). On top of the B-Square riser I put a long 11mm Airforce scope rail to move the scope to rear. On top of that I put my Sightron SIII series 10-50×56 LRMD scope in Sportsmatch adjustable ATP61 mounts.

The whole setup is in the picture. Looking at the accuracy results this setup seems to work well for now.

FWB P70 scope mounting

FWB P70 scope mounting


First Accuracy test (@ 50 meter / 55 Yards)

5th of November 2014

The Feinwerkbau P70 at the outdoor range. Paper targets at 25 and 50 meters

The Feinwerkbau P70 at the outdoor range. Paper targets at 25 and 50 meters

Yesterday evening I took the P70 for its first shooting. I set up paper targets at 50 meters / 55 yards on our outdoor range at Field Target Schalkhaar. The weather was nice and calm with a temperature of 10 degrees Celsius and no wind at all. And luckily no fog. Excellent weather for testing. I had 3 batches of JSB 8.3 grain Exact available. I set the P70 on my front rest and rear bag for benchrest style shooting.

The air cartridge was filled to 180 bar. I did 5 to 6 five shot groups with each batch. The first (long type) air cartridge lasted for 55 shots. The second one for another 25 shots.

JSB Exact Batch 80000013 resulted in an average of five shot groups of 24.50mm measured outside to outside (33, 19, 35, 22, 22 mm). For the average I exclude the first 33mm group because this was used to adjust the scope.

Batch 21000013 resulted in 18.75mm average group size over 4 groups of five shot (19, 16, 20, 20 mm)

Batch 11007609 resulted in 20.00mm average over 5 groups of five shot (20, 21, 22, 21, 16mm). Last group of 30mm was excluded because  the air cartridge had reached 100 bar and the last shot dropped low.

1. Testing the Feinwerkbau P70 for accuracy at 50 meter

1. Testing the Feinwerkbau P70 for accuracy at 50 meter (click for larger image)

2. Testing the Feinwerkbau P70 for accuracy at 50 meter

2. Testing the Feinwerkbau P70 for accuracy at 50 meter (click for larger image)

It looks like the P70 accepts the different  pellet batches quite well. In other words: It is not pellet fussy. And the overall result of 18,75 mm group size over 20 shots in total and 20mm over 25 shots is very satisfying. The smallest group of 16mm is on par with my Walther rifles. Next thing is to shoot it in the Field target shooting position to see how it shoots.

I’ll keep you posted.


 Summary: How to convert a Feinwerkbau P70 to a Field Target Rifle

To convert a 7.5 Joule /  6 FPE Feinwerkbau P70 to 16 Joule or 12 FPE field target rifle I used the following parts ordered by email from http://www.hasselhorst.de.

Table 3. Feinwerkbau P70 parts that I used for the conversion from 7.5 to 15,5 Joule

4.9.0203 Druckfeder (schlagbolzen) Compression spring (for firing pin) J1 P70FT 3.77
3.2.008.304 Klappe Flap / Latch for the loading slide T2 P70FT 37.76
3.2.034.307 Lagerschraube Firing pin spring screw N1 P70FT 5.70
4.9.0011 O-Ring 25,2 x 3,0 O-Ring 25,2 x 3,0 F1 P70FT 1.8
3.2.034.305 Schlagbolzen Firing pin P2 P70FT 30.57
3.2.036.220 Zwischenring, 20,4 Joule Intermediate plate, 20,4J V2 P70FT 44.16
1780.106.9 Zylinderschraube (Deckplatte Absorber) Cylinder head screw A1 P70FT 0.91
4.9.0001 O-Ring 4,0×1 (Abdekplatte Absorber) O-Ring 4,0 x 1,0 F1 P70FT 1.8
3.2.004.301 Deckplatte (Absorber) Cover plate U1 P70FT 11.18

1. The parts in the list above were installed. To mount the regulator in combination with the spacer (20.4J intermediate plate) I needed four new M5 bolts of 30mm long. The absorber system was removed and the cover plate installed.

2. The pressure regulator was adjusted to 100 bar output pressure (the regulator set screw needed a turn of about 90 degree to get to 100 bar. Clockwise and with a brass tool). The result was max 220 m/s with 8.4 grain JSB Exact pellets.

3. To get a higher velocity I milled the transfer port in the barrel holder (that goes from regulator to valve house) to 5mm diameter under a 10 degree angle. (I advise not to do this with a drill because the drillbit will wander off and may damage the expensive barrel holder) and the velocity was up to 234 m/s. A small adjustment of the firing pin spring brought the velocity to 239 m/s or 15.4 Joule / 11,4 FPE


An Other Way to get the Feinwerkbau P70 running at 16 Joule / 12FPE

Searching and reading some more about Feinwerkbau FT rifles on the internet I found a French forum where Alpazen commented on my conversion ( http://www.afft.fr/forum/viewtopic.php?f=9&t=2023 ). He commented that he would have kept the original striker and strikerspring. To increase the energy to 16 Joule the valve return spring should then be modified.

I thought this was interesting because the original striker is much lighter  (20 gram vs. 35 gram for the FT striker) and would in combination with a lighter striker spring probably cause much less shot reaction and vibrations. Potentially increasing the accuracy. It could also possibly decrease the air consumption by reducing hammer bounce.  This approach would also save shooters that are going to convert their own P70 some 40 euro for not having to buy the FT striker, strikerspring and strikerspring adjustment screw (numbers 3.2.034.305, 4.9.0203 and 3.2.034.307)

So I wanted to test this and replaced the mounted FT striker, adjustment screw and FT strikerspring with the original 7.5 Joule P70 parts. I put the Combro CB-625 on the barrel and played around with the striker spring preload. The maximum velocity I got was 220m/s (13 Joule with JSB Exact 0.54 gram). I experimented with increased and reduced regulator pressure but this did not help to get a higher velocity. The 100 bar setting was quite optimal.

Next I removed the valve housing and valve to check the valve return spring. It is a stainless steel (at least it is not magnetic) spring made from 0.60mm wire. I looked in my bag (nicely assorted 🙂 with 500 different springs all mixed up) for at least 20 minutes before I finally found a spring with the same diameter but a thinner wire. It looked a bit like a spring you find in a ballpoint pen. This spring had 0.40mm wire. It was about double the length of the original so I needed to shorten it and flatten the cut end to make it the same length as the original spring.

Original P70 valve return spring

Original P70 valve return spring

Calculations show the new 0.40mm wire spring has only 20% of the force of the original 0.60mm spring. This results in a faster opening of the valve, more valve lift and longer valve open time. All letting more air through to the pellet.

After assembling everything back together  with the new valve return spring in place and the original 7.5J striker and strikerspring I tested the velocity again. And it was at 236 m/s. That’s 15 Joule. Some small adjustments on the strikerspring preload increased this to 241 m/s or 15.7 Joule or 11.6 FPE. Five subsequent shots showed a small difference in velocity between them (2 m/s).

So Alpazen was right! You do not need to replace the striker, strikerspring and strikerspring adjustment screw to get the Feinwerkbau P70 from 7.5 to 16 Joule. This reduces the cost of a conversion a lot. You only need the 20 Joule spacer to increase the regulator volume, an o-ring for this spacer, the cover plate for the Absorber hole with o-ring and screw. And if you have the courage to saw down your loading slide latch you can even save on buying the short version. The conversion would then be around 60 euro for the parts.

One thing I noticed in this new setup is that the valve is open when there is no air pressure. This is not any problem but when an air cylinder is screwed onto the rifle the air will flow out through the open valve and out of the barrel. To prevent this you just need to cock the rifle before screwing on a cylinder. The cause of this is that the valve return spring is now weaker than the strikerspring and pushes the valve open in the un-cocked position.

I will need to test this setup for air consumption and accuracy. Will report back.


Feinwerkbau P70 Field Target mounted in the Feinwerkbau 700 Aluminium Stock

The P70 is still on the light striker, strikerspring and the valve return spring. The news is that I bought an Aluminium Feinwerkbau 700 stock for my P70. I’m spoiled by my Walther LG400 Alutec stock so the wooden FWB p70 stock did not feel right anymore. I could not get comfortable with it in the sitting FT position.

I tried to buy an aluminum FWB 800 stock but my preferred supplier Waffen Hasselhorst made a phonecall  with Feinwerkbau and they said the P70 would not fit in the 800 stock. Not even with alterations/milling/machining. The 700 stock would go they said but would need some machining. I have seen and handed the FWB 700 stock that Bert B. a fellow Dutch shooter is using.  Quite some improvement over the P70 laminate and P70 aluminium stock.

So I decided to order the FWB 700 ally stock in silver and black with gripsize M. When it arrived after 7 days I was surprised to see it had the grip, cheeckpiece and hamster from the model 800. Not the laminate grey/black/white anymore but full black. And the hamster is an aluminium one. The older 700’s have a laminated wood hamster.

It took more machining than I first thought to fit the P70 in the 700 stock. But the result is nice:

Milling space for the P70 cocking lever.

Milling space for the P70 cocking lever.

Milling of the fore stock is finished.

Milling of the fore stock is finished.

 

1. Feinwerkbau P70 in FWB 700 aluminium stock.

1. Feinwerkbau P70 in FWB 700 aluminium stock.

 

2. Front side view of the Feinwerkbau P70 in the Feinwerkbau 700 aluminium stock.

2. Front side view of the Feinwerkbau P70 field target rifle in the Feinwerkbau 700 aluminium stock.

3. Feinwerkbau P70 in 700 ally stock.

3. Feinwerkbau P70 field target in 700 ally stock.

I added two barrel holders. The rear one supports the barrel and the front one supports only the air cilinder and leaves the barrel free floating.

Apart from milling the hole for the cocking lever I also needed to machine the cocking lever itself to reduce the width and had to modify the hamster. Enlarging the hole for the cocking piece in the fore stock removes the part where the clamp normally sits to attach the hamster in the fore end rail. Moving the hamster forward is the easiest option to overcome this. But that exposes a part of the system block and brings the levers of the cocking mechanism in view. Not a neat look. I made new holes in the aluminum hamster to move the clamp forward while the hamster stays in the rear postion to cover the system block.


December 14, 2015
Velocity results with the Feinwerkbau P70 Field Target Rifle

I bought me a Blueshot cable (see: http://www.zbm2.com/blueshot/ ) for the Combro CB625 chronograph (see: http://www.chronoscopes.com/ ).

This cable with the accompanying Blueshot software allows to connect the Combro to a cell phone to store the data of the shotstring.  Much more convenient than pressing the button on the Combro after every shot, and writing down the velocity. And more convenient than dragging a laptop computer out into the field. The shotstring data can emailed in comma separated values (CSV) format from the Blueshot app to an email adress. It is easy to import the CSV file into Excel.

I used the Feinwerkbau P70 to see how the Blueshot and the P70 did perform:

Feinwerkbau P70 Field Target; Shotstring in meter/second (blue) and feet per second (red).

Feinwerkbau P70 Field Target; Shotstring in meter/second (blue) and feet per second (red).

meter/sec feet/sec
Number of Shots 38 38
Average 239.6 786.0
Minimum 238.3 781.9
Maximum 240.2 788.2
Extreme spread 1.9 6.3
Standard Deviation 0.5 1.7

As you can see the velocity is very constant: 1.9 m/s (6.3 fps) difference over 38 shots. Pellets used were JSB Exact 0.54 gram. The pressure on the cilinder manometer was 100 bar at the end of the shotstring. This explains why the velocity seems to drop somewhat after shot number 30, because the regulator output pressure is set at 100 bar.

IWA-FWB03_JPG

Feinwerkbau P70 regulator and valve cut-away view.

Advertisements

14 thoughts on “Feinwerkbau P70 conversion to 16 Joule / 12 fpe for Field Target

  1. AWESOME write up as usual ! What next ???

  2. You really did a fine job! I am working on a sencond hand P70 at the moment, but can’t get is right… I think the main reason is that several parts are different from the parts in the partlist. My P70 has parts of the RT, the FT and some springs which are clearly self-modified :(. Well, I guess I just have to order the original parts first…
    Anyway, thanks for your clear explanation!

  3. Very clear and informative write up. Could a C60 be converted do you knw?

    • Hi Dan,
      I have never looked into converting a C60. So I really don’t know.
      Best thing would be to compare the exploded views of both models and look for the parts that are different. (The Feinwerkbau website has these )
      My guess would be that it is not a straight forward swap of parts like the regulator. That’s because the C60 is the predecessor of the P70 and I have not read of conversions.
      But that’s just a guess.
      Best regards, Sven.

  4. Thanks for the reply. Yes I looked at the diagrams and there is nowhere for screws for the regulator. the block is completely different to the P70. Maybe just an airtube conversion which has an internal regular may work.

  5. Isn’t the C60 CO2 powered? If so, conversion might be impossible since the pressure can’t get higher then approx. 60/70 bar (evaporation of the fluid CO2 results in a maximum pressure, above this pressure the co2 doesn’t turn into gas anymore). You might get some result in a larger transfer port and stronger striker/hammer spring. But it could also result in inacurracy because of the fact the valve opens too long.

  6. Yes its CO² powered but I want to replace the CO² cylinder with a CZ S200 cylinder to make it a PCP 🙂

    • Hi Dan, Does the CZ200 cylinder use the same thread size as the FWB C60?
      I think it could be done the way you describe, but would require more work and setting up.
      Keep us posted please when you get on with this project.
      Sven.

      • Unfortunately not so an adapter was required. Adapter and a tench external regulator are fitted. Power adjustment was a bit of a pain to keep it below 12ft/lbs i put 2 small thin washers behind the hammer spring and it was well over, take one out and it was well under 😦 So it was a case of emery paper on the second washer to get it within limits. I now get 65+ shots @ 780 fps with +/- 5fps from a 175 bar fill. Accuracy is stunning so I am very happy with it so far. I also cut some excess barrel sleeve off and made a stripper so barrel is just longer than the cylinder. It doesn’t look at all bad 🙂

  7. Hi, did you have to apply some lock to the regulator screw (the golden screw) after turning it ? I have a P700 and turned about 15 minutes clockwise, the speed rised, but after a few trainning sessions the screw returns to its original position by itself ? Is it necessary to insert another washer along with the other 10 that are already inside the air chamber ? Thank you.

    • Hi Haguen,
      Is it the Feinwerkbau 700 (without the P) that you have or the Feinwerkbau P70?

      I have a P70 in a 700 stock. And mine does not change in power. But maybe it is different for the 700.
      Did you mark the setscrew and learned the changing position from that? Or did you notice a drop in velocity?
      It could also be that the velocity drop is caused by something else.
      For my P70 an extra belleville washer was not needed. It works fine with the original 10. But I have read different stories on that. Other users have added 1 or even 2 extra washers. It would help in keeping the pressure on the setscrew. On the other hand should the higher pressure needed to get 12fpe be sufficient to keep the setscrew in place.
      I would advise to mark the setscrew with a sharpy to make sure that’s the culprit.

  8. Thank you for the reply,

    Like in the picture “P70 regulator adjustment screw” in this topic, i turned the golden screw 15 minutes clockwise and marked the position, after a few training sessions noted that the speed returned from 183 to 174 m/s and the mark in the screw also returned 15 minutes counter clockwise.

    A have two 700, without P, rifles, one was adjusted by a technician and the other i am trying by my self, noted that the silver pin, that crosses the adjustment screw and contains the washers, is in a diferent level among the two rifles, the one that was adjusted by the technician seems to have less one washer, like if this washer was removed to decrase the air chambers size, this rifle always shoots above 182 m/s and the adjustment screw keeps its position.

  9. Hello Sven,

    Thanks for your great webpage!
    I have been reading it for along time.
    I am currently converting a FWB C60 to PCP

    Living in sweden our limit for free airguns are 10Joules, may get a permit for it and bring it up to 16Joules in the future

    Check this out:
    http://www.luftvapen.info/viewtopic.php?f=1&t=16888

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s