Walther shot reaction Absorber and Equalizer systems

Research by Steyr showing the movements of 4 types of airrifles

Recoil in PCP airrifles?

A lot of shooters think pre-charged pneumatic airguns have no recoil. But shooters that are keen observers will notice that these rifles do raise their muzzle at the shot. Even the relatively low powered 7,5 Joule / 6 fpe rifles show a reaction to the shot. The picture above is from an old Steyr advertisement and shows barrel vibrations of the Steyr LG100 rifle compared to three other makes (my guess is Feinwerkbau (red), Anschutz (dark blue) and Walther (light blue)). Steyr was at that time ( I guess mid 1990’s?) one of the first to use a “Stabilizer” system to counteract the recoil. A plunger inside the bolt is released by the shot impulse and is pushed backwards by a small spring. Feinwerkbau (starting with the 603 rifles) uses some air from the shot to push a plunger backwards.

These movements at the release of a shot are caused by:

1. The acceleration of the pellet in the barrel and

2. The air jet that leaves the muzzle when the pellet exits.

There is also movement caused by the movements of the hammer/striker that opens the firing valve. The general principle  to reduce or eliminate these movements or vibrations is to create a moving mass in the opposite direction.

Recoil absorption in Walther airrifles

Walther PCP air rifles have devices installed to reduce or eliminate the movement of the rifle when a shot is fired. The use of these Absorber (LG300) or Equalizer  (LG400) systems started with the introduction of the LG300 rifle.

In the LG200 rifles (that preceded the LG300 series) a system with 7 small steel balls inside the hammer was used. These reduce the bounce of the hammer and thus prevent more movement than necessary to open the firing valve. This can reduce the back bouncing movement of the hammer and thereby vibrations  and air consumption.

1. LG200 Striker with balls inside

LG300 Spring driven plunger type Absorber system

The LG300 series introduced an spring loaded Absorber (pict. 2 and 2A). Some air from the shot is directed backwards through the pellet probe (no. 26) and a plunger (no. 27) moves backward against a spring to counteract the forward moving pellet.

2. Walther Drawing no. 265 07 11 LG300 Spring Absorber

 

2A. Cut away view of the LG300 spring/plunger type Absorber system

 

 

 

I have used an 7.5 joule LG300 with this type of Absorber for some years. I noticed that this old spring driven plunger type Absorber is not as good in reducing felt recoil compared to the Steyr and Feinwerkbau systems. Probably the reason why Walther developed a newer and better Absorber system. 

LG300 XT Pneumatic driven Absorber

The next version is a pneumatic system in the LG300 XT series (pict. 3 and 4). The absorber mass (no. 30) is pushed backward by some air form the shot. It hits a cushion of air inside the hole in the breechblock and at the end of its strike meets a soft cell foam pad (no.32) to stop it. It can be adjusted by a screw from the top of the breechblock. This screw adjusts the opening through which the air can leave the chamber behind the absorber mass. It regulates the speed and amount of movement of the absorber mass.

3. Walther Drawing 268 11 02 LG300XT Pneumatic Absorber

LG300 XT Pneumatic Absorber

 

LG300 XT pneumatic absorber

The LG300 and LG400 Magnetic Absorber / Equalizer

 

5. Walther Drawing 275 23 10 LG300XT Protouch Magnetic Absorber

The newest version is used in the LG300 XT Carbontec, LG300 Pro-touch (pict. 5) and in the LG400 (pict. 6). In this system the absorber mass (pict. 5 no.27) is held forward with a magnet (no. 26) . The impulse of the air the hits the pellet probe at the shot. This impulse (shock) overcomes the magnetic force. Then the absorber mass is pushed backwards by a spring. The Magnetic Absorber does NOT use any air. There is no channel in the pellet probe to guide air backwards. It is only the shock of the sudden air pressure on the front of the pellet probe that overcomes the magnetic force that keep the pellet probe and magnet together. The spring force is used to drive the Absorber mass backwards. 

Picture 6 is from the LG400 and shows part no. 29 in two different versions. One with and one without the load indicator (top) that shows if a pellet is loaded in the barrel. Originally the LG400 cheaper Basic or Economy did not have the load indicator but these days it seems all LG400 versions do have the load indicator system.

6. Walther drawing 277 73 98 LG400 Absorber/Equalizer

The 16 and 21 Joule Walther field target and hunter rifles.

All the above shown systems are for the 10 meter 7,5 Joule versions of the Walther air rifles. The LG300 Dominator and LG300 Hunter rifles at 16 and 21 Joule do NOT have such a system. They still use the old type pellet probe (pict 7. no 26) that is assisted by as spring (no. 30) to keep it closed.  This loading system dates back to the LG200.

7. Walther Drawing 266 81 90 LG300 Dominator. No Absorber is installed

 

LG300 Absorber and Dominator Pellet probe

Testing Absorber functioning

An recoil absorption system is used in the Steyr 16 Joule LG110 FT rifles and when correctly set up seem to make quite some difference in perceived shot reaction.

So I have the idea to test the difference in shot reaction between my converted LG300 with spring absorber and my LG300 Dominator without one. For that I need to buy an accelerometer and equipment to read it’s signal. I got some good info on this from Sighter. He tested his 16 joule LG400 with the magnetic absorber on and off. This showed that the absorber still does something at 16 Joule.

LG400 Absorber On (courtesy Sighter)

 

LG400 Absorber Off (courtesy Sighter)

 

---

 

 

 

Walther LG400 cut away view

Adjusting the Walther LG400 Absorber system

Added in July 2021: There is a youtube movie by Walther of how to adjust the Absorber. Its of course much better to watch a Walther professional mechanic do this than to read my write up below.

 

BEFORE WORKING ON YOUR RIFLE MAKE SURE IT IS SAFE TO WORK ON IT!

• CHECK THAT IS DOES NOT HAVE A PELLET IN THE BREECH OR BARREL
• REMOVE THE AIR CYLINDER (PRESSURED AIR RESEVOIR)
• FIRE THE RIFLE 3 TIMES IN A SAFE DIRECTION TO MAKE SURE ALL THE PRESSURED AIR HAS LEFT THE RIFLE AND THAT IT IS EMPTY OF PRESSURED AIR

The LG400 Absorber or Equalizer system can be adjusted very easily by the user. There is an adjustment screw on the outside of the rifle for this. (see drawing below).

The Absorber works by moving a piece of steel (the Absorber mass (yellow)) backwards by a spring (blue). This Absorber mass is held in its forward position by a magnet (red) inside the Absorber mass. This magnet sticks the Absorber against the rear of the pellet probe (green).

Walther LG 400 Absorber system cut-away-view

The impulse force of the shot against the pellet probe overcomes the magnetic force and the Absorber mass is propelled backwards by the spring. The Absorber moves backwards inside a channel (a hole) in the breech block that is closed at the end with an end screw.The fit of the Absorber in this hole is so tight that the air inside the hole cannot escape quickly enough. Air pressure is built up by the moving Absorber and this acts as a brake, slowing down and finally stopping the Absorber movement.

This channel or hole in which the Absorber moves has two very small ports at each side of the breech block to let some air out. The amount of air that can flow out through the ports is restricted by a small grub screw on top of the breech block, in the center of the dovetail.  This screw can be adjusted to let more or less air out. This affects the movement of the Absorber.

When the ports are fully closed the Absorber moves only a short way and brakes very hard. When the ports are fully open the Absorber moves fast and will not brake, it will hit the buffer that sits on the end screw.

Both the situations are not optimal.  By screwing the adjustment screw in or out the travel of the Absorber can be controlled.

With the adjuster screw turned out (up) you can see when the ports are fully open when you can see through the holes at the side of the breech block.  Hold it against a light.

The amount of travel of the Absorber is visible through a slot (yellow in the drawing) in the breech block. This is the slot where the pin that moves the pellet probe goes through.

To adjust the Absorber and to see how far it moves you have to shoot the rifle with a pellet. Without a pellet fired the Absorber will react differently and in some rifles it may not even move at all.

Before changing any setting it’s good to check how far the Absorber moves. You can do this by shooting the rifle with a pellet loaded (make sure you have a safe backstop!) and holding the rifle still and horizontal, lying on a table for instance. After the rifle has been fired take something soft, a toothpick, and use it to push the Absorber mass further backwards through the slot in the side of the breech block. If your Absorber has 3 to 4 millimeter movement left it is quite well adjusted. This is an optimal setting in my rifle.

If you find your rifle kicks too much (has a lot of shot reaction) and it looks like your Absorber has some travel left (more than 3mm) you could adjust the screw.  Turn the screw at the top out (counter clock wise) for a quarter turn and try again.

If there is no travel left you need to adjust the set screw inwards (clockwise).

It can also be that the rifle kicks because the Absorber mass hits the rear screw with buffer. In  that case you need to close the ports by turning the screw in (clockwise) so the braking force of the air is increased. In this case it may look like you have some Absorber travel left. But that is because the Absorber bounces back from the buffer.

It’s a good idea to write down any adjustments you make, or measure the depth of the adjustment screw with a caliper, so you can always return to the original setting.

Walther LG 400. The Absorber adjustment screw is the small grub screw visible on the right hand side on top of the breech block.

 

LG400 Magnetic Absorber System

 

1. LG 400 Absorber. (the upper pellet probe has no load indicator, for the LG 400 versions without Absorber system and load indicator)

 

 

2. LG 400 Absorber

 

 

3. LG 400 Absorber

 

 

Instructions for Installation of the Absorber system in the Walther LG400 
By ‘Louis’ O’Connor

Disassembly:

Remove the cylinder, de-cock the action and clear the barrel with a safety line
before starting work. [Part numbers] as per Walther drawing LG400_System_2777398_g.pdf,  {see drawing below}

The stock is fastened to the barrelled action by 4 screws:
• One [62] under the front barrel clamp (3mm hex) [5].
• One at the rear of the fore-end, below the regulator (3mm hex). The fore-end rail [2] (‘hamster’) must be removed to access this screw.
• Two screws at the side, at the rear of the receiver (4 mm hex).

{Sven: the above disassembly instructions are for the LG400 Blacktec rifle only, the other LG400 types use only 3 screws: Two in the front barrel clamp and one at the rear of the fore-end below the regulator}

The Equaliser/Absorber cavity plug [28] is Loctited in, so the dismounted barrel action needs to be clamped carefully in a vice. Use a tight-fitting 4mm Allen key and be prepared to use considerable force. Some gentle local heat may also help break down the Loctite.

Before removing the loading lever assembly [3], note that the click-stop spring [39] and ball bearing [38] are held under tension by a grub screw (2mm hex) [63] alongside the trigger. Wind this grub screw out until flush with the receiver body or the ball bearing will fly out.

Hold on to the loading lever when loosening or tightening the loading lever shaft retaining screw [44].

Reassembly:

Apply a very light layer of Teflon* oil to the Equaliser counterweight [31] before insertion and Teflon grease on the loading lever shaft [13]. (*n.b. Steel/aluminium contact)

Insert the counterweight assembly [30]. Use a wooden cocktail stick to align it if necessary, ensuring the notch is in line with the loading lever shaft [13].

Use a dab of Teflon grease on the ball bearing [38] to hold it in position. Push it down into its well before inserting the loading lever shaft [13]. Carefully line up the studs on the loading lever bell crank [15] with the holes in the two toggle links [7, 18]. Refit the collar [20], cap [21] and screw [44] to the far side of the loading arm. Lightly tighten click stop grub screw [63].

Clean the cavity plug [28]. Glue on the buffer pad [32] with a strong adhesive; shoe glue (rubber solution) should be OK provided that no petroleum spray solvent, eg., Transyl. WD40, etc, is later used in this cavity. {Sven: I used superglue}

Lightly Loctite the plug thread and install the plug [28]. Torque to 1Nm.

Lightly apply Teflon grease to the stock/barrelled action mating surfaces and the paper shim. Refit barrelled action and stock (it drops in forwards and pulls back).

Replace the rear central action screw first, then the front, ensuring that the threads are not crossed. Check for central alignment and then fit the side screws to finger tight. Tighten all screws until they stop. Test weapon with dry firing.

Refit cylinder and test for real, with pellets, adjusting recoil counterweight roughly [screw 94]. Check for bedding anomalies.

Torque central screws to their maximum by hand, using a standard 3mm Allen key,
Torque the side screws to 2,5Nm in two stages using a torque screwdriver and a 4mm Allen head. Retighten the centre screws and final torque the side screws to 3 Nm (up to 4Nm max).

Reassemble the fore-end, etc, of the stock as necessary and finally adjust the recoil counterweight’s movement as required before refitting the sights.

N.B. Moving the loading lever to the left side allows the user to move the sights forward enough to access the Equaliser adjusting screw [94] without the loading arm binding on the windage knob. Unfortunately, the loading lever then turns against the thread so the screw will need thread locker to hold it.

© ‘Louis’ O’Connor, July 2017
{many thanks to Louis for this excellent write up, Sven}

Walther LG400 Exploded view