GTA
General Discussion To Gateway To Airguns => Airgun Gate => : redroush00 June 20, 2010, 04:40:59 AM
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Saw this somewhere.
"One thing I did find out was that as the spring piston rifle heats up, your shots will change. The more I shot it, the better it grouped and as I adjusted the scope to bullseye, it was getting dead-on. I then let the rifle cool down and picked it back up after shooting the Gamo Shadow 1000 for a while. After cool down, I noticed that it shot good groups, but it shot them lower and to the right a bit. So heat definitely has an impact on spring air rifles. Probably more so on magnum spring rifles as the piston is sure to get more heat than lower fps rifles. Email me your thoughts on this."
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Red, I don't think internal temps play much of a role in target deviation because the heating and cooling within the shot cycle is so fast that they cancel each other out so to speak. More likely the cause of poi change is everything from ambient temprature (outside the gun environment), direct/in-direct sun light, barometric fluctuations, etc. The poi shifts seem to be compounded with scoped rifles too IMHO. Just my two cents. tjk
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The internal heating from shooting a spring will have no impact in the accuracy of the springer because the temperature change would be nearly if not zero. There is no way that a person could ever shoot a springer fast enough to create a heating condition within the compression chamber.
However.... if a gun is "cold" and zeroed in and the gun is subjected to sunlight or extreme heat conditions and changes, the accuracy could change with the temperature. This could involve the air temp and compression chamber as well as the metal expansion and contraction.
I think what you will find is a leaking seal in your gun and that as the gun "cools", that it is not the gun cooling down but rather the lube that is getting past the seal is thickening and changing the compression ratio.
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There's something to it, but I'm not sure what. I've had springers that need a few "warm up" shots before they'll settle down and group properly. Not a big deal if you're just shooting paper, but really irritating when you miss a starling that you KNOW you should have hit. I think it may have something to do with the lubes taking a set between shooting sessions, and needing a few shots to free them up. I also suspect it's worse with guns with loose tolerances that rely on heavy tar to tighten things up, but that's just a theory, no actual data to back it up. Don't know what the shooter from your quote was shooting, but it's been my experience that this is only impacts the first 4 or 5 shots, if he had to shoot a long string to settle it down, I'd say he has something else going on. Later.
Dave
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I don't know about the parts heating up inside due to the shooting. But if I haven't shot a certain airgun for a week or more...it'll need a couple of shots to make it's shots consistent. Maybe it needs the lubes to circulate around.
But definitely heat affects the scope(s). Just this afternoon I was shooting and the first few dozen shots were dead-on. And then for about 30 something shots....the accuracy was terrible. After adjusting the scope's turrets a few times the cross-hairs settled down. I keep my airguns upstairs and the temperature was 28C....I shot in the basement and checked the temps....and it was 21C.
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My Gamo Big Cat will never put the first shot where it's sighted in. I've seen it off as much as 2" at 25yd. After that it settles down. Not a good pest rifle. I prefer CO2 for that reason. As long as the pressure is up it shoots where you hold.