A lot of shooter 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 10 meter 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 in 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.
Walther PCP air rifles also use devices 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.
The LG300 series introduced an spring loaded Absorber (pict. 2). 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.
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.
The newest version is used in the LG300 XT Carbontec, 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) . Some air from the shot goes backward and overcomes the magnetic force. The absorber mass is pushed backwards by a spring. 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.
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 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.
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.
Adjusting the Walther LG400 Absorber system
The LG400 Absorber or Equalizer system can be adjusted very easily by the user himself. 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).
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.