Some small air rifle adjustments.

Sometimes small things make all the difference.  Small things like a small turn of an allen key. Have you ever heard the old saw “speed kills”?  Air guns that have been “tuned” for velocity as their primary goal tend to sacrifice accuracy. Diablo pellets are largely drag stabilized projectiles and require clean steady airflow across their surfaces to perform consistently.

As diablo pellets approach the speed of sound (1100 fps approximately) the forces upon the pellet change, drag force is increased ex potentially  and the flow of air is more chaotic. The result is the destabilization of the pellet.  This effect begins as low as 925 feet per second. This is why bullets which are primarily designed to travel above the speed of sound look so different than air gun pellets. So is too much velocity the death of your airgun accuracy?

I have an affection for Weihrauch HW 100 air rifles. But I think the factory may have made a small error. Not in design or construction. When I first started shooting my “100” it was launching Beeman Field target  specialspellets at 1050 feet per second.  At thirty yards it would place three shots on the target touching with two “fliers a half to a quarter of an inch away every time.  Moving to a heavy pellet (Crosman 10.5 premiers) helped a bit.  I knew the solution was in decreasing the velocity via internal adjustment. 

Use this information at your own risk: In performing this modification you may void your warranty! I accept no responsibility for damage or misuse.  Check your local laws  if you are thinking of increasing the output power.

So I changed it.  The tools required were a set of metric Allen keys and a chronograph. Remove the air cylinder from the air rifle by unscrewing it from the receiver. Remove the action from the stock by extracting the two allen headed stock bolts.  Remove the receiver end cover with the two small allen headed bolts.  Remove the trigger group’s two allen headed bolts.  While slowly opening the action and looking through the rearmost screw hole that mounts the trigger group you will see a small grub screw. Carefully remove this screw.  Adjustment of velocity may commence when you re install the trigger group and the air cylinder.  Small adjustments of the large allen headed bolt under the receiver end cover will make big differences across the chronograph. I did this with the action out of the stock.  When satisfied replace the grub screw to lock the setting. Complete reassembly. Test the safety,  Enjoy!

So what did this do for me?  My air rifle ( in .177) was shooting about twenty one foot pounds from the factory.  I set the power to about seventeen.  That is shooting Crosman premier 10.5 grain (CPH) also known as Premier Ultra Magnum at an average of 858.8 Feet per second over 56 shots. That's four fourteen shot magazines.  The first Magazine average was: 843.9. The second: 859.9. Third: 866.9. Forth: 864.6.  Highest velocity was 873.2 which is 14.4 feet per second above average. And the lowest which was 835.0 which is 23.8 feet per second slower than average.  This low occurred on the first shot of the first magazine.  The results have been a dramatic increase in accuracy shot to shot and an increase in air use efficiency going from about forty five shots to more than sixty.  

Rick Klages