Having some issues with my gun when the temperature starts rising throughout the day. When I sight-in in the morning and shoot later in the heat of the afternoon POI shifts an entire MIL low. Could a regulator creep and stay at a higher PSI due to the heat? It will stay grouping and entire MIL low. Not just the first shot. It's not the scope changing POI I have tried three of them. Can't seem to figure it out.
Could a regulator creep in the heat and stay at a higher pressure?
- Thread starter FastPellet212
- Start date
Reg creep I doubt as root cause 
More typical could be any of the following ....
Receiver / chassis parts & barrel attachment to scope rail / mounts shape / position shifting in the heat creating a changing POI
Barrel bands that contact barrel out at end of air tube or bottle
* If Not at a know distance such as FT where parrilax focus determines range estimation ? ..... Internal scope calibration due to heat ( Common problem ! )
More typical could be any of the following ....
Receiver / chassis parts & barrel attachment to scope rail / mounts shape / position shifting in the heat creating a changing POI
Barrel bands that contact barrel out at end of air tube or bottle
* If Not at a know distance such as FT where parrilax focus determines range estimation ? ..... Internal scope calibration due to heat ( Common problem ! )
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I guess I am just going to have to make multiple dope sheets.Reg creep I doubt as root cause
More typical could be any of the following ....
Receiver / chassis parts & barrel attachment to scope rail / mounts shape / position shifting in the heat creating a changing POI
Barrel bands that contact barrel out at end of air tube or bottle
* If Not at a know distance such as FT where parrilax focus determines range estimation ? ..... Internal scope calibration due to heat ( Common problem ! )
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How about the hotter air being less dense? I noticed with both my long range capable guns that the poi is high when it's hot out(relates to the range and where in the parabolic travel the pellet is for your setup and initial zero, tilted base etc) but the regs and plenum are cool and indoors. I did have a gun get hot, forgot, and at 55 yards shot a full 10 inches high and made a spicey sound. Looked at the plenum pressure and it was way high. It took 3 shots to level it out.
Don't be flustered by this, you got good data and can plan for it in the future!
Don't be flustered by this, you got good data and can plan for it in the future!
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This may sound silly but, where are you shooting and is your barrel "free floating"?
I shoot facing south (in my car port) and when the sun settles in the west, the sunlight heats up the barrel unevenly and the poi changes. It totally drove me nuts till I figured it out.
I shoot facing south (in my car port) and when the sun settles in the west, the sunlight heats up the barrel unevenly and the poi changes. It totally drove me nuts till I figured it out.
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So I don’t think it’s heat related regulator creep. I say this because I live at 5000ft in the desert of SW Utah so I get huge temperature swings everyday. Additionally, my barra 250z has a tiny 15cc plenum and even though my reg is set at 2800psi it’s not weird for it to show as high as 3000… here’s the thing. If I ever get a POI shift it’s maybe a half mil (max) up. Never down. Creeping up should lead to a higher velocity not lower…. However, the barra having the HPA storage over the barrel gives it some ridiculously good barrel harmonics so that could be a factor.
Have you chrono’d to see if you’re getting speed changes? Because if you aren’t my money is on your Optic. Could be the gas it’s sealed with leaks or is susceptible to heat. Or the glass could be expanding as it heats up. I’m no expert though and prepared to be wrong about ALL of it haha.
Have you chrono’d to see if you’re getting speed changes? Because if you aren’t my money is on your Optic. Could be the gas it’s sealed with leaks or is susceptible to heat. Or the glass could be expanding as it heats up. I’m no expert though and prepared to be wrong about ALL of it haha.
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As does elevation ... being an Air Density issue. Thinner air due to Hotter temps or Higher elevation will speed things up while projectile BC value also increases.
Lower elevation and Colder air things slow down and BC value decreases.
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100%… I’m between 3k and 5k on a daily basis. I tend to hunt around 3k-4K… when I go up real high I generally don’t change anything lol. Just rezero and appreciate my slugs flying flat as $@“&… but if I was gonna stay at high altitude I’d definitely retune.
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So I chrono'd the gun after shooting in the heat and the FPS does go up, but for whatever reason my POI shifts low. IDK what is going on.
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What distance is your zero set for? If it normally hits the X ring at 50 yards but hitting low at something like 20 then the pellet may well still be climbing through its ballistic curve and with a higher pressure is moving faster than when you originally set your zero. Then shoot at a target 15 yards further than what the gun is zeroed for. Let the gun cool off in an air conditioned room for a few hours, make sure your air tank is fully charged and see where it is hitting before it gets hot.
Rick H.
Rick H.
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So, I sight in at 30 yards and when I take the gun back out int the morning when everything has cooled off its at its zero again.
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I bet that’s the problem, the pellet is moving faster and hasn't climbed as far when it’s hot. Try it at 40 and 50 when hot, I’ll bet it isn’t shooting low.
Rick H.
Rick H.
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Yeah that’s what he meant, kind of. He meant shoot it at 40 and 50. The pellet travels in arc, meaning first it climbs upwards, reaches its peak and then goes down. Like a stone you throw. At 30y, your zero, it is still traveling upwards. If it gets hot and the pellets travels faster, it’ll be at 30y earlier on its journey than when it’s going a little slower in the cold. Ergo you hit low at 30y. At 50y you’re probably past peak so that normally you’d hold a little higher with your 30y zero. Try your usual hold for 50y when you’re hitting low at 30 because it’s hot. You’ll probably hit high now, meaning you need a little less holdover.
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