Airgun Accuracy

Only accurate airguns are interesting!

Walther LG400 Temperature Test

On the Shooting-the-Breeze.com and also on the Pimpmyairgun.com forums I got the advise to check the LG400 for point of impact (POI) shift due to temperature changes. Someone was convinced that the way I had done the 7,5 Joule to 16 Joule conversion would certainly lead to POI changes when the ambient temperature changed.

I do not think this is a real danger because the LG300 pressure regulator that I use is not temperature sensitive. Proven so and used by plenty shooters from all over the world on their field target rifle for over many years. And Walther solved the problem with the temperature sensitive firing valve over a decade ago in the LG300 Dominator. The LG400 has a flat firing valve and a hard black polymer valve seat. Both features reduce the chance of temperature sensitivity.

The adapter that I made to fit the LG300 regulator on the LG400 rifle is a short aluminum bushing that sits between two o-rings. It is floating between the o-rings and does not touch the breechblock directly. To me it seemed highly unlikely that this could cause temperature sensitivity.

To test the temperature sensitivity of the LG400 in the  16 Joule conversion I decided to put it in the freezer and to shoot it to see what would happen.

LG400 before freezing with temp sensor attached

LG400 before freezing with temp sensor attached

A temperature sensor was attached to the breechblock and the temperature of the rifle was 18.2 Celsius / 65 Fahrenheit (bottom number on the display of the thermometer). I put a paper target at 50 meters / 55 yards and shot a 10 shot group and recorded the velocity. It was a rainy evening and the wind was playing around from left and right so I had some horizontal spread in the group. But in the vertical plane the spreading was not to bad. The average velocity over 10 shots at 18.2 Celsius  was 236.3 m/s with a extreme spread of 2.9m/s.

LG400 in the -25 degree Celsius freezer

LG400 in the -25 degree Celsius freezer

Thermometer showing the rifle is 1.5 Celsius.

Thermometer showing the rifle is 1.5 degrees Celsius.

I put the whole rifle with scope and all in the freezer at -25 Celcius / -13 Fahrenheit and left it there until the temperature of the rifle had reached 1.5 Celsius / 35 Fahrenheit.

I took the rifle to the shooting range and tried to shoot it at the 50 meter paper target again. Unfortunately this did not work out. Because of  heavy condensation on the lenses of the scope I was not able to see the target at all. I tried to wipe the lenses but within seconds the condensation was back.

Condensation on the rifle and scope after freezing

Condensation on the rifle and scope after freezing

Condensation on the rifle at 5.5 Celsius.

Condensation on the rifle at 5.5 Celsius.

So I just did 10 shots over the chrono while keeping an eye on the thermometer.

Shot Temp (C) Temp (F) Velocity (m/s) Velocity (Fps)
1 5.4 41.7 237.2 775
2 5.7 42.3 237.0 780
3 5.7 42.3 236.6 775
4 6.1 43.0 232.8 776
5 6.1 43.0 234.5 780
6 6.3 43.3 234.8 773
7 6.3 43.3 233.4 770
8 6.7 44.1 233.4 775
9 7.1 44.8 235.4 772
10 7.3 45.1 235.9 775
Average 235.1 775
E.S. 4.4 9.5

The temperature had already risen from 1.5 out of the freezer to 5.4 Celsius when I started shooting over the chronograph. During the shooting temperature increased to 7.3 Celsius at the tenth shot. There is no trending relation between temperature and velocity in this data.

Average velocity with the cold rifle was 235 m/s compared to 236 m/s with the rifle at an ambient 18 Celsius / 65 Fahrenheit.

After about 10 minutes the temperature of the scope had increased somewhat and I was able to see a very hazy image of the target for 20 seconds or so when I dried the front and rear lenses with a cloth. So I decided to try to shoot at the 50 meter target and clean the lenses before every shot. The rifle had a temperature of 7.8 Celsius at the first shot and 13.3 Celsius at the tenth shot.

10 shot groups at 50 meter. Top left at a rifle temperature of 18.2 C bottom right with cold rifle (5.4 to 7.3 C)

10 shot groups at 50 meter. Top left at a rifle temperature of 18.2 C bottom right with cold rifle (7.8 to 13.3 C)

The picture shows the 10 shot groups with the ambient temperature and cold rifle. Top left group is at ambient temp and bottom right is at a temp between 7.8 and 13.3 degrees Celsius. Both groups show quite some horizontal spread caused by the wind. The cold group is also not a nice one because I needed to clean both lenses of the scope before every shot and then quickly take a shot before the condensation was back.

But what is important for this temperature test is that the average center of both groups in the vertical and horizontal plane are almost the same.

Conclusions:

Average velocity  of Walther LG400 rifle at 16 Joule differs by -1.2 m/s (3.9 fps) when the temperature of the rifle drops from 18.2 degrees Celsius to 5.4 degrees Celsius (65 to 42 Fahrenheit). This 1.2 m/s difference is smaller than the normal velocity spread observed in field target rifles at a constant temperature.

A temperature drop from 18.2 to 7.8 degrees Celsius  has no effect on the point of impact at 50 meters / 55 yards.

I think it is safe to say that the Walther LG400 in the 16 Joule conversion is not temperature sensitive for point of impact in the temperature range between 5.4 and 18.2 Celsius (42 and 65 Fahrenheit).

2 thoughts on “Walther LG400 Temperature Test

  1. Sven, thanks for your huge effort and sharing this with us. Super valuable information.

    Gert

  2. Its near on impossible bringing a colder scope out in to a warmer temp and trying to use, many a time had to scrape ice off lenses much colder than your test. 13c about average west European temp, need to take it to 100 degrees. Some countries run 120+ degrees not surprising haven’t seen much shift.

    Easy way to tell is clamp the rifle up rigid as in solid, get an impact point and watch it move as temp rises. Early one from April 2012, done same with Anchutz, Steyrs and many others, you will be amased what moves and where. http://i1140.photobucket.com/albums/n563/Jonhareng/Shooting%20choice%20of%20champions/FENP800FROZEN0001DSCN4043.jpg

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