I have long suspected that barrel temp and the residual lube film inside the barrel have a critical impact. When it is warmer ambient the lube film is softer and the bullet slips through with less resistance/velocity loss. Shooting 100 and 200 yard bench rest with a 22rf, a cold barrel first shot typically drops low and left, with my heavy barreled rifles as much as a foot or more.
As the barrel warms up the ammo returns to the pervious zero. An a cool (60 degree) morning the first relay sitting shots require 4 or 5 to get back on the mark.
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I've always wanted some sort of method for measuring barrel temp shift as I shoot to see if this is all my imagination}
Barrel mass and resistant to temp change is a big factor as well. My heavy barrel 22 rf Ruger bench rifle can take a bunch of ammo to get to working temp. My CCJohnson Martini with a much smaller di. barrel warms up a lot quicker.
In hot weather, a 15-20 min cool down between relays usually only requires a shot or two, depending on barrel mass, to return to zero. When the ambient temps are below 50 or so it requires more shots. Sometimes at the Spring 22 shoot (or at the our last Fall match
) when temps may be in the high 30s or low 40s it can require 1 dozen or more shots--even if I plug the barrel at both ends between relays.
I strongly suspect that in addition to special low-drag-when-cold lubes than may not build up much of a residual film, Biathlon ammo has a powder/primer blend that is more stabile in low temps. It may be that biathlon rifles never really warm up so that most shots are "cold barrel" shots or they have learned a hold-over pattern that allows them adjust point of aim with each shot.
I think we could learn a lot from the Biathlon shooters I'd like to know more about that site.
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Lowest 22 RF Temp (Read 9502 times)
