My assumptions that a regulator is a one way pressure control valve. So if last shot you take is at a cold temperature then much later you take your next shot at a much higher temperature the pressure in the plenum will be higher than the regulator's set pressure by the ratio of (273+C1)/(273+C0). The shot will be faster. If you do the reverse last shot at a warm temp. followed by the next at colder temperature the shot may not be slower because an ideal regulator will just let more air into the plenum correcting the pressure drop. However the temp. difference has to be significant as defined the equation. If this is the case then in some cases what is called regulator creep can be pressure changes due to temperature changes.
Regulator creep or temperature changes
- Thread starter BlackICE
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great question,i have notice my (480) fx crown bottle gets warm when i fill & after some time psi will drop from 250 bar to 240-245.could that be the same??? tks
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Correct on the pressure. But the speed of the shot truly depends on your hammer settings. A higher pressure can lead to a slower shot just as well as a faster one.
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I have only experienced this to be true in higher temps on the reg side, when hunting several times in freezing temps, my tank pressure and efficiency will decrease, but on the reg side, it holds, as long as the tank pressure is above reg setting of course? Also some regulators if not all? Do vent to atmosphere at over pressures just not on the set spot usually, I suspect huma’s are pretty good at that as they seem to do it a little less on the high side? This is why most first shots or two in almost all guns (that I own) are low, great question
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I’d assume that is why you should dry fire the first round in a session. That goes with after a fill but also for temp/barometric pressure at the time.(?) I’ve never experienced this but I always dry fire to set the regulator before a shooting session.
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I agree I came to the same conclusion after my 1st shot on a warm day was much faster than the rest of my shots and the previous shot was done on a cold evening.
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I’m curious as to what the FPS spreads are from this first shot to the second on your guns. What spread is acceptable, or considered normal?
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I don't normally dry fire the first round after filling. The reason being the hammer and pressure settings are delicately tuned to the slug. The slug itself provides a seal (gas check) inside the barrel that is part of this equation. If you don't want to waste a slug, then use a heavy JSB pellet, but I've never been successful having the 2nd shot reflect the regulator settling in when dry firing. I've only been able to achieve this when pushing a projectile through it that allows adequate back pressure. I'm not saying the first shot after filling won't be wonky. I always fire it off, but I use a projectile for the aforementioned reasons. I have dry fired in the past, and I have gotten the reg to settle in, but it normally takes 2 or 3 shots vs one shot with a projectile in the breech. And those shots to me are a waste of vital air. Just my $.02 though.
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Cant speak for Blake ice. But when I tune a regulated gun, I'm happy with a 10fps above or below the average on a first shot. If its 20-30 fps off, the hammer strike isn't adjusted optimally for the reg pressure. Unless it has a serious creep issue.
See, an unregulated gun will hold a tight extreme spread over a 500 psi pressure range. Same holds true for a regulated gun that may creep 500psi if the hammer is adjusted properly.
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