I did a test to compared the FPE difference by just changing the pellet weight
I tethered the gun to my scuba tank. The pressure on the thank was 2350-2400. I figure I kept the pressure constant and took the average of 8 shots on each pellet. I figured it would give a good reference. It would have been nice if the tank had the pressure at 2600-2700 psi. This is close to the peak of my shot string anyway.
JSB Kings 25.4g @ 903 FPE 46
HN Cudas 31.02g @ 846 FPE 49.3
If I remember correctly (I could not find my notes on the pellets test) when the gun was stock I only got a 2fpe gain between the pellets. But I'm not positive on this.
It is a shame that the Cudas don't group well. Group I got was around 1.5 in compared to .5in with the JSBs. It might be acceptable for hunting. Also the gun in quieter with the cudas
It is actually shooting a little faster than what my chart above but off by 4 fps
. If I assume that they are using the same amount of air, the efficiency on at that psi would go up from 1.453 to 1.558. This is a rough estimate but it should be some what close to that.
If I assume that the increase of speed is linear between the two pellets, My gun with the current set up maxes out at 975 with the JSBs (53.6FPE) then the Cudas should somewhere around 910fps which will mean 56.9 FPE. not bad with the size ports that I have.