really pending on guns caliber, power wanted and what size passage is currently.Fill in those Q's & we can discuss it further
Quote from: Motorhead on June 17, 2021, 12:04:40 AMreally pending on guns caliber, power wanted and what size passage is currently.Fill in those Q's & we can discuss it furtherKral puncher breaker, .22, 30 to 35 ftlbs, and I dont know maybe 1.5 inches to barrel from valve exhaust. Whatever the stock length is
My nemesis was pushing 18gn JSB over 1000fps with some sort of aftermarket hammer spring.
Quote from: Insanity on June 17, 2021, 12:12:35 AMMy nemesis was pushing 18gn JSB over 1000fps with some sort of aftermarket hammer spring.I have a interesting situation where I have a maybe 12mm of spring that doesn't ride the rear guide rod, was planning on making a tss for it because with a front guide it's just begging for it
I bought my nemy used and dont know much of its history other than it was tuned to be HOT. I think the only major difference is I have a drop block for a bottle, from what I understand is that the rest of the action is the same. Is your goal up to 35FPE because I think a spring like I have would be the easiest way to hit that goal. Outside of that I cannot provide a better answer to get to a FPE value or efficiency by adjusting the transfer port size.
Compensate for the long passage, and the potential pressure drop that creates, by a small increase in pressure.... Flow velocity is important only towards the end of the shot cycle, when the pellet is reaching maximum speed.... Initially, just after the valve cracks, you are dealing only with the effects of pressure.... Port size, port restrictions, and port length have little to do with what happens in the first inch or two of pellet travel, when the acceleration is the highest....Bob
If you calculate the volume of the transfer port (from valve seat to pellet base), you add that to the volume of the plenum (or reservoir if unregulated) to get the increased volume before the pellet moves.... That expansion drops the pressure by P1 x V1 = P2 x V2.... which rearranged is P2 = P1 x V1 / V2....For example, if you start with 2000 psi in the plenum (P1), and have a plenum of 50 cc (V1) and a transfer port volume of 1 cc (expanded volume V2 = 50 + 1 = 51 cc), the pressure available at the start of the shot is 2000 x (50 / 51) = 1961 psi.... If the transfer port volume is 2 cc, same pressure and plenum, you end up with 2000 x (50 / 52) = 1923 psi.... That would require increasing the pressure in the plenum by 38 psi to compensate for the larger transfer port volume....If the transfer port is significantly smaller than the caliber, then in addition you MAY get a loss in flow because of the additional restriction because of the added length, but that will very much depend on the velocity.... Any such loss would require an additional pressure increase to compensate.... Bob
https://www.gatewaytoairguns.org/GTA/index.php?topic=120119.msg1179362#msg1179362Read reply 25Some more here https://www.gatewaytoairguns.org/GTA/index.php?topic=153468.msg155688769#msg155688769
yes ... that inconsistencies in path size hurt more than too small or too large.The rotary ball valve controlling velocity is a major stumbling path in that design.Valves transfer path exiting throat all the way to and including barrel really optimize in these @ sizes for more powerful field duty type tunes..177 cal @ .140".22 cal @ .165".25 cal @ .180"GETTING said sizes not so easy on some PCP's
Good information. Ive always wondered about this effect. Good to have the math! Thanks.