Grouping

[achard]

I bought barsto .40 cal ramp and fitted in my new gun. My question is, would it will affect the grouping if you keep on changing bullets. I normally use teflon coated for practice and fmj / tmj for competition. I Need your comment and suggestion.

Thanks,

[spook]

I bought barsto .40 cal ramp and fitted in my new gun. My question is, would it will affect the grouping  if you keep on changing bullets. I normally use teflon coated for practice and fmj / tmj for competition. I Need your comment and suggestion.

Thanks,

<{POST_SNAPBACK}>

I cannot prove anything, but I think it does. Recently I switched bullets (not from a different brand, but a different lot). The groups opened up noticably. After I ran a brass brush through the bore, groups were getting tight again.

My totally unscientific explanation is that the bullets "fill up" the barrel in certain places and kind of form their own profile, specific to the bullet you use.

The good news (if my theory is corect at all) is that it is easily fixed by cleaning the barrel.

[Patrick Sweeney]

This is a phenomenon some guns show, and others do not. Usually you only see it with a Ransom rest, where the human variable is out of the equation. Typically you see it in .22LR, where changing from one brand to another can cause groups to expand.

When I've run into the problem, brushing the bore and shooting a few groups to re-condition the bore with the new load solves the problem. Some guns don't care squat, they'll shoot the same regardless. Some few care, but will settle back down after a magazine or two.

Rarely will a gun not shoot when you change. It just takes a bit of time and work with some.