They aren’t really needed for power but for increased shot count and lighter hammer load at the same power due to the lower reg pressure.
I maxed out a raw .357 with a 81grn pellet at 960fps without a plenum but cocking effort was high and shot count was terrible.
Agreed, I made one and didn’t like the way it altered the balance on my hunting gun but for benchrest, forwards weight is not so detrimental.
About 5 -6 years ago there was a guy in Cyprus who fitted a second 500cc buddy bottle at the rear of the action to act as part of the stock, this sent reduced pressure air to the front buddy bottle which effectively became a huge 500cc plenum. This keeps the weight balance towards the stock but compromised aesthetics.
Bb
As per my understanding 1cc of plenum is ideal to produce 1ftlb energy.
Practically it's neither possible nor feasible for high powered guns.
The maximum acceptable relationship between plenum volume and energy is 1cc plenum to produce 3 ftlb.
Definitely it would be achieved by increasing the regulator pressure.
Now one can achieve 1000 fps with 40 gr projectile at 180 bar reg pressure using 3.5" tubler plenum but I would never take this route if I have to achieve that power level.
I would increase the volume of the plenum.
To me as the new HMX block has integral plenum of around 30cc, adding 50cc external plenum should be good enough to produce almost all kinds of required high powers while keeping the regulator pressure from 140 bars to 150 bars.
Very high reg pressure like 180 bars requires heavier hammer and / or heavier spring.
The other counter productive thing is that at high reg pressure, there is more wear and tear of parts. Shot count becomes low. The firing cycle doesn't remain nice.
However, in my personal RAW HM1000X guns I use 35cc external plenum. I don't use heavy slugs. I mostly use pellets.
With 35cc external plenum and 150 bar reg pressure I can push .22 JSB 25 grain redesigned pellets upto 1000 fps.
To gain more power, I would either need more reg pressure or larger plenum or longer barrel.
Am I right ?
Bhaur
