jeepkahn wrote:Gippeto, You may have hit SOS, depending on what sos was that day(everybody talks about temp effecting sos, but they forget that humidity, and barometric pressure play a part as well)...
Everybody seems to think that the only way heat is generated in air is from compressing it, with enough pressure velocities in the muzzle can well exceed the sos due to "choke heating" and the LOCAL sos(inside the chamber/muzzle) can be higher than atmospheric sos, so that even though the velocity is over the atmospheric sos, it's not moving faster than the local sos(this is why evacuating the barrel is more effective in subsonic guns than super/hyper sonic guns, the vacuum raises the local sos or mach# if you will)...
Muzzle blast in airguns is a non issue unless it is humid and you start getting condensation plumes, if you look at the paintball kit for chronies, the muzzle is pretty much point blank...
And wouldn't it be pretty easy to just fire 5 shots,start at 1ft and moving a foot each time, should settle it pretty quick...As long as you have consistent ammo and pressures...
I've been playing with GGDT and small barrels on large valves and have been getting interesting results. I will need to chrono a few shots to see if GGDT is even in the ball park. When I get into the realm of warning the barrel may be choking the flow, some of the speeds are well above the SOS. For example on my 1 inch valve, using a 3/4 inch screw on barrel 10 feet long, a 2 gram projectile (miniature marshmallow) and 200 PSI puts the speed well above SOS. I need to buy a chrono.
I've seen the same thing if I screw on a golf ball barrel on the not yet built 3 inch 200 PSI cannon. I should have results this fall but I like what GGDT predicts.
Using a light projectile about 1/2 the mass of a golf ball and using the following;
Gas Air
Temp 80 F
Pressure 200 PSIG
Outer Diam 12 inch
Inner Diam 3.3 (QDV coaxial style)
Length 22 inch
Valve type Barrel seal (QDV not listed)
1 valve
Efficiency 45% (probably low but using default)
Piston Diam 3.1 (had to make it bigger than the seat for GGDT)
Mass 24 oz (wild guess at just under a couple lbs)
Vent diam 1 inch (needed something for GGDT here)
Pilot volume 20 in3 ( the bumper trigger area )
Bore 1.59
Length 164 inch (long barrel also tried 120 inch (10 ft))
Friction 0.1 psi (roll in projectile)
Mass 20 gm (foam ball. GB is about 46 gm)
Diameter 1.56
Initial position 0.
This gives a muzzle prediction of 1511 FT/S.
I hope to try it late this summer. The heavier GB will still be subsonic
1085 ft/s isn't bad.
