I own 4 different 22rimfire rifles. All are bolt action rifles. All have decent scopes. One is old. One is semi old, two are new in the last few years.
They are a CZ 455 American, a CZ 452 trainer, A kimber 82 Government, and an old(circa 1950) Winchester 72A.
I took them all to the range today to give them a workout. Things went well. Probably even better than I expected.
The two CZ rifles both shot under 1/2 inch at 25 yards and nearly the same at 50 yards with match ammunition. The Kimber did about the same. The 452 trainer shot a 1.2 inch group at 100 yards when the wind stopped. I can usually put 4 out of 5 shots in one hole with a close flyer at 25 yards with any of these three rifles.
The Winchester never has shot match grade groups for me but doesn't need to for squirrel hunting which is what I have used it for during the last 56 years. With match ammo or Federal Auto match it shoots about 5/8" at 25 yards and about 3/4 inch at 50 yards. With high speed ammo it runs about 3/4 inch at 25 yards and 1 inch at 50 yards. Basically minute of squirrel.
This is the background for the rifles.
My problem, if you want to call it that, is when I change ammo type or brands in any of the newer rifles, I get a significant impact point shift. Sometime up to 1.25 inches at 25 yards.
This happens even when using differing match ammo brands. Group size stays about the same, it is just in a different spot. When I go back to the brand the rifle is sighted in for, the impact point goes back to center just as you would expect.
I thought the heavy barrels on the target rifles wouldn't do that to the extent that it is happening. I expected the impact point to vary only slightly but the group size to change a bit.
That isn't what is happening.
The really funny part is what happens with the old Winchester 72A. The center of the group never moves. The groups simply change size with a change in ammunition quality. It doesn't matter whether I use target ammo or high velocity ammo, it all goes into a group centered on the x ring.
Why is this happening this way?
The three newer rifles all have free floated barrels. The CZ rifles are magazine fed. The Kimber is a single shot.
The Winchester is fed from a tube magazine beneath the barrel. No possibility of free floating there.
Another thing about the old Winchester. About 45 years ago, I mounted a 1 inch Bushnell 4X scope on it and sighted it in. I have never needed to change the adjustment on the scope in all that time. It still shoots to the same impact point after all these years.
I expect I will take it hunting again this fall when squirrel season comes in. It will still do the job.