GTA
General Discussion To Gateway To Airguns => The Shop => : Bogey June 19, 2009, 05:32:50 AM
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Had to re-sight scopes on 2 of my AGs today since I had installed new and better scope mounts on both AGs. I had more or less sighted them in last night before the rain hit. I set up the bench and the rest that I use, got the pellets and all the other stuff I needed. The air temps where over 95 degrees when I brought one of the AGs out from an Air Conditioned house. I thought to myself that the metal of was mighty cool (about 75 degrees) compared to the air temps. Anyway, everything was set and I took the first shot. Way off. Way Way off. What the heck? The shots went everywhere in about a 4 inch circle.
This called for some thinking. All screws tight, etc. Then I thought about the chilled AG being taken into the heat. I decided to wait until the temp of the AG reached something closer to the air temp. After about 15 minutes I tried again to shoot a group. After the 1st shot I was glad that I had left scope adjustments alone. The shots where hitting just as I wanted, centered and 1inch high.
The only thing I can attribute this to is the difference in the temps of the AG, the scope, the mounts and even the stock compared to the Air temps. This caused unequal expansion / contraction somewhere in the AG platform. And until it equalized it was going to shoot off.
I tried a few shots with the 2nd AG and got almost the same results ( different caliber.22 vs .177) . After letting the 2nd rifle reach outside temp it placed shots like I wanted.
So if you take your AGs from one enviroment to another you may want to give the Ag time to reach the temps where you will be using it.
Just an observatiion on my part.
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I think you're absolutely right. I've read reports that extreme temperature changes affect the tension on the crosshairs in the scope. This alone will drastically alter the poi. Also, since airguns use compressed air instead of an explosion like powder burners, the firing cycle of airguns will also change with temperature. All we have to do is remember pv=nrt from our high school science classes.
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Affects the lubes, too. Also, don't let your gun sit in the hot sun. It can become very warm, plus a barrel shaded on one side will actually warp a bit from expansion on the sunny side.
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Also how evenly tight the stock and scope mount screws are will affect the expansion and contraction rate of the airgun and its parts. I've read that serious competitors cover their guns to shield from heat or cold during a match when not shooting. And always rest the gun in the same position.
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I have the same problem here where I live. When I am going to shoot I just walk outside and set my gun on my shooting bench and leave it out there for an hour or so then I go outside and shoot away. This seems to solve most of my accuracy problems. It was so bad at one point that I thought my 350 or scope was broken cause the groups were all over the place.
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wow i just came inside from shooting my b28 in 22 with a brand new hawke scope. my groups were all over the place, i was just about to break out the remington 1100 12 guage out frustration. i stopped logged on and read this thread, now it all makes sense i live in sw florida and is sooooo hot here. thanks guys.
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lil'feeby, I just saw your comments on your scattered hits in the heat. This is what I experienced and I had made sure all the fasteners where properly firmed up on both the rifle and the scope mounts. After the AG came up to the outside air temps, it started hitting like it had the night before. I was glad I had waited because I came very close to removing the scope and checking everything out. I had taken the AG from about 75 degrees to at least 95 degrees in the sun.
Things expand and contract and AGs are no different. I suppose we need to take it into consideration when moving from one temperture extreme to another.
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I've had a similar problem but not quite the same. I live with no AC, my guns are always at ambient temp. What I noticed is that my POI is off by 3 to 4 clicks at several ranges when the temp got up to the 100's. Frustrated at first - then I remembered the "A Team Scope Set Up" and how they have different elevation settings for the different temp ranges. At first I thought 'I'll never become that nit-picking.' After I had zero'd in my AG from 10 yds to 55yds I was pretty happy with my accomplishments. I had done that work while the temps were in the low 80's. It wasn't until the 100's came around that I noticed I was way off with my POI, but my groupings were consistent. So,,,guess I do want to be more nit picking,,,,back to the zeroing range and make charts for the different temp ranges. Previously I almost wouldn't have believed such a difference. My guess is that springs inside the scope have different tensions when they get warmer.
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Went shooting yesterday with a few friends....started at 10a.m with a temperature of 26C.....around 78F. By 1p.m the temps have risen to 30C....86F or so....and the POI were starting to change. All our shots were going high with some windage movement. Guess the metals expanded and the lubes inside were more liquidy....making the piston and parts move faster which equal a little more power and speed (?).....maybe.
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first of all to live in tall. with no a/c is major. you must have some zen powers or something. second, is it the springs in the scopes or is it the spring in the piston? is it a combination of both? i would like for some gas ram guys to chime in on this one, now you guys gat me all curious.
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I noticed it first on my PCP rifle so I'm guessing its mostly the springs in the scope. However everything seems to be adversely affected by heat - even my hand pump for my PCP. I noticed on the same day that my pump gets pretty warm on these hot days and I can't compress above 2400 - I need 3000 - only thing it will do is seemingly get locked somehow: can't suck in anymore air to compress. I pull up on the handle to suck more air in and a vaccum pulls the handle back down. I do have one window AC unit in the bedroom so we can sleep well. I put the pump in there (80 degrees) for a couple of hours and it would work just fine then.
With my springer rifle the groupings were worse than my PCP (which previously were just as good) so perhaps the piston spring is affected also, at least a little. I like the idea of gas rams. Don't have one,,,,yet.
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yes sir buddy, i am starting to warm to the idea also. i read a review of the new crossman nitro, thinking about selling some blood or something to get one.
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Never thought of that.....but that's true. In warmer/hotter weather when we pump up our PCP's.....we're literally sucking in hot air and then add in the heat generated from the friction of the pump.
I've only pumped up my PCP'soutside in only 75F temps....which is not bad. During the hotter days.....over 85F I've only pumped them up indoors....which is abit cooler and bring the pump along to the shoot, but never needed a refill....yet.