All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"
Regulated plenum vs reservoir volume .257 160fpe
mackeral5:
I am considering adding a regulator to my .257 that is the subject of this thread:
https://www.gatewaytoairguns.org/GTA/index.php?topic=181490.80
Normally I would just start testing, but rather than just going into a process of investing a bunch of lead and nitrogen I thought I would see if I could get some help here in making some calculations, to directionally see if it is a worthwhile venture.
I have the parts to assemble a 160cc regulated plenum and 340cc HPA storage tube. The 340cc storage is rated for up to 3600psi.
Let's just assume I can get the gun to perform 160fpe around 2500psi reg setpoint. And just to be safe let's assume a low efficiency of 1.0:1. I am pretty sure I can tune for significantly better than that, but let's at least have a realistic starting point.
How many shots should I be able to get on a 3600psi fill? If the number is 10 or more, it's a no-brainer for me to proceed. If it is 10 or less, I won't be quite as interested but may still convert to regulated.
Thank you in advance for your insight.
Scotchmo:
You should get 10 shots, maybe 11 or 12 with the last two falling off the reg.
rsterne:
You have 340 cc of air, and 1100 psi of headroom (fill pressure minus setpoint).... If you get 160 FPE, at 1.0 FPE/CI, you will be using 160 CI per shot.... You have available (340 / 16.4) x (1100 / 14.5) = 20.7 CI x 75.9 bar = 1570 CI of air available.... As Scott says, that should, in theory, net you (1570 / 160) = 10 shots, if you can get an efficiency of 1.0 FPE/CI at your 160 FPE goal.... If you can do that and tune on the knee, so that the velocity ticks up a few fps when you hit the setpoint, you could get a couple more by shooting below the setpoint by ~200 psi.... If you can get higher efficiency, your shot count would increase....
Bob
mackeral5:
Thanks for the responses and thank you for your patience in sharing the formula for the 10000 time.
I am going to add it to my spreadsheet this time.
mackeral5:
Just a quick update. I set the Huma right at the 170 bar mark. The tune is currently around 150-155fpe. I am low on nitrogen so further testing will have to wait for later in the week. Air consumption seems to be in alignment with what is described above.
So far I really like shooting this long barreled .257 under regulation. it is very different from shooting a 34gr pellet shooter at 100 yards.
More to come next week.
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