Recently purchased a Benjamin Akela PCP in .22 cal. Tested the out of the box stock gun with Air Arms Diabolo Field 16gn pellets at maximum velocity (using the dial on the receiver), and got the following visualization using chronograph data:
The velocity peaks on the third shot at 970 fps, and drops off successively afterwards, losing 4%, down past 931 fps by the 18th shot. Not very many shots to ensure on-target for a hunting session.
After reading the excellent article about tuning un-regulated airguns located at Hard-Air magazine:
(https://hardairmagazine.com/ham-columns/bobs-guide-to-tuning-unregulated-pcps/)
I quickly figured out that the hammer-spring was too powerful at the max setting to get the desired bell-curve. I did not want to use the provided power adjustment knob, because the knob does not adjust hammer tension, it just restricts the transfer port opening & I was suspect of how it would work. So instead…. I watched a great YouTube video from Sub-12 Airgunner in the UK on how to disassemble my new Akela (https://youtu.be/EwWQi_R5-n8), and found a few others by searching “how to shorten a coil spring”, and took 2 coils off of my Akela hammer spring, made sure that the pre-load adjustment screw was backed all the way out, re-assembled the rifle, and re-tested, with the following results, again using Air Arms Diabolo Field 16gn pellets at “Max” on the receiver’s power adjustment knob:
Now, I get a full 60 shots (5 full magazines) of shots at velocities between 835-870 fps (4% variance). Note that I reach and stay above 835 fps on the 15th shot, with the bottle pressure at about 2,620 psi. At higher bottle pressures, the hammer doesn’t have enough force to open the valve long enough to reach that velocity, so instead of completely filling the bottle to the maximum of 3,000 psi, I now only fill it to 2,600 psi.
Very happy now with this $600 budget PCP, am getting very good results (1 MOA) with pellets (JSB Hades are the best) out to 50 yards, and started today testing some slugs to see if I can find one that yield 1-MOA accuracy at 75 yards or more.
The velocity peaks on the third shot at 970 fps, and drops off successively afterwards, losing 4%, down past 931 fps by the 18th shot. Not very many shots to ensure on-target for a hunting session.
After reading the excellent article about tuning un-regulated airguns located at Hard-Air magazine:
(https://hardairmagazine.com/ham-columns/bobs-guide-to-tuning-unregulated-pcps/)
I quickly figured out that the hammer-spring was too powerful at the max setting to get the desired bell-curve. I did not want to use the provided power adjustment knob, because the knob does not adjust hammer tension, it just restricts the transfer port opening & I was suspect of how it would work. So instead…. I watched a great YouTube video from Sub-12 Airgunner in the UK on how to disassemble my new Akela (https://youtu.be/EwWQi_R5-n8), and found a few others by searching “how to shorten a coil spring”, and took 2 coils off of my Akela hammer spring, made sure that the pre-load adjustment screw was backed all the way out, re-assembled the rifle, and re-tested, with the following results, again using Air Arms Diabolo Field 16gn pellets at “Max” on the receiver’s power adjustment knob:
Now, I get a full 60 shots (5 full magazines) of shots at velocities between 835-870 fps (4% variance). Note that I reach and stay above 835 fps on the 15th shot, with the bottle pressure at about 2,620 psi. At higher bottle pressures, the hammer doesn’t have enough force to open the valve long enough to reach that velocity, so instead of completely filling the bottle to the maximum of 3,000 psi, I now only fill it to 2,600 psi.
Very happy now with this $600 budget PCP, am getting very good results (1 MOA) with pellets (JSB Hades are the best) out to 50 yards, and started today testing some slugs to see if I can find one that yield 1-MOA accuracy at 75 yards or more.
