Condor SS velocity puzzle
Did a 25 shot string & got high 835 low 820 avg 826. Exactly what I wanted. Probably could have gotten more shots but I was running low on pellets. So I cranked up the pw to see what max power had, pw 3-13, 3000psi, got: 968, 961, 949, 953 & 950. That’s fine with me, cause I think with 37gr rat snipers the velocity will still be ok.
So here’s where my question comes from. 2400psi fill, backed the pw back down to 1-2, started shooting & got these #’s : 847, 844, 846, 855, 858 & 848.
I don’t understand why if before I cranked up the pw I was where I wanted to be & after I picked up 20fps. Top hat is tight, no movement. Help me understand.
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The quick, but not usually satisfying answer, is that there are some big non-linear behaviors in the hammer and valve system. This means small changes can have a big effect, sometimes in a direction other than you’d think.
If you take apart the mechanical actions going on in one shot, you’ll see the complexities.
The hammer strikes the breech/tophat/valve system.
The (poppet) valve unseats. Air flows into the firing chamber. Firing chamber pressure rises.
O ring seals on breech and valve tighten their grip due to firing chamber pressure.
Valve spring compresses, tending to close the valve.
The difference in pressure between tank and firing chamber tends to close the valve also. This closing force changes a great deal depending on valve lift and chamber pressure rise. The higher the chamber pressure, the lower the closure force. The higher the valve lift, the lower the closure force (poppet valve physics).
The amount of time the valve stays open is related to the closure force of the valve spring and closure force from pressure difference. Also related to inertia of breech/tophat/valve system and clamping force of O ring seals.
The amount of time the valve stays open and the valve lift determine the amount of air pushing the projectile down the barrel. More air, delivered earlier in the process, leads to higher projectile velocity.
So, there are competing factors of varying strength that lead to the muzzle velocity we measure.
Most of these forces are not so easy to measure, but can be estimated with some effort. The gas gun is an interesting machine. It’s not as simple as it looks…
Most folks work on achieving consistency from shot to shot, at the right muzzle velocity, using the minimum of air. This forum contains a great deal of information on how to get the most from a gas gun. Good luck. Have fun!
-x356b