Your 50% and 950fps is a realistic goal.My 40% and 1060fps is a realistic goal.50% and 1060fps is impossible.
QuoteYour 50% and 950fps is a realistic goal.My 40% and 1060fps is a realistic goal.50% and 1060fps is impossible.I would generally agree with that conclusion, for most typical PCPs.... but I'm pretty sure Marco won't.... .... I don't know where his thread is where he posted the results that gave 60%, hopefully he will link to it.... as I think you may be surprised what can be done with a short barrel and high pressure (I certainly was!).... I did find some partial information in this thread, check out my calculations in Reply #87.... Unfortunately there are no pics any more.... https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE.... The result of interest is 331 m/s (1086 fps) with 45.5 gr. @ 270 bar = 119 FPE = 60%As I said in that thread from 2018, my "lofty goal" formula needs a tweak for situations where the air mass is small and/or the bullet mass is large.... .... If I did the math right, in this case they are about equal.... Bob
No reliable photo hosting, all the pictures seem to vanish after some time. Most annoying. Need to see if I can find the pictures from my old phone. Well the gun is not your average build, valve has been used to make 7-800fpe on .457, 11.5 or 12mm peek poppet radius seat on poppet 11mm port in to 10mm mirror finish transfer, all edges radius, barrel is hand lapped to a very long lead in, about 100-150mm, cant remember the correct value. But the bullet gets to move very easily.Its about how fast you get the air behind the bullet not the flow until the bullet starts moving. After that you want max flow all the way to the muzzle. I don't care about air consumption, air is the most easiest consumable in this hobby. I like racing and pushing the envelope.Will be pushing it further again when spring comes, have bigger valve and double air capacity for the twenty at works. Marko
Is there an error here......The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE
https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE.... The result of interest is 331 m/s (1086 fps) with 45.5 gr. @ 270 bar = 119 FPE = 60%As I said in that thread from 2018, my "lofty goal" formula needs a tweak for situations where the air mass is small and/or the bullet mass is large.... .... If I did the math right, in this case they are about equal.... Bob
I think it's quite simple, Scott.... The entire 45 gr. of air does not get accelerated to the muzzle velocity of the bullet.... ...I simply don't believe that the entire air mass ends up travelling 1086 fps.... Do you see any reason that must be the case?.... Marco's numbers pretty much prove otherwise, don't you think?....Bob
...The porting idea came from Lloyds maximum velocity test, when he used the pellet stationed in the breech with cams and full reservoir pressure behind it.BIG valve and ports to feed the barrel should give similar results. Well it works. How does the models take in to account barrel friction and possible lubrication? We use silicone to lube the pellets. ...Marko
Yes rifled barrel, can't remember the twist, maybe 8" Conventional porting, valve seat almost at the bend. Good looking setup you have! I just missed a furnace from one auction. Would be fun to cast some of the not so critical parts. Marko
... I tell people my 50% lofty goal is intended for a slug doing about 950 fps.... and is invalid if the velocity is significantly lower than that.... Bob