cold bore accuracy

[grant moore]

After some time consuming tests with differnt reloading charges my 7mm rem mag has groups in the sub MOA. My problem is my cold bore shot is excellant, however the next 4 or 5 hit low. The grouping remains sub MOA however is lower than my cold bore shot. I use a silencer that I remove after every shot to let the barrel cool down since it is a sporter barrel. Time between shots is approx 3 to 5 minutes.. My bore is fouled, not clean..

I am not sure if I should be bedding this rifle or not.. Not sure if this would benefit me or distroy a very accurate rifle and ammo combination.

Any suggestions would be greatly appreciated.
Grant

Example 300 Yards, cold bore bulls eye.. next 3 shots 1.5 inches low with a group of .75 inches.

 

[benchracer]

Your description doesn't sound like you have a bedding problem. If the rifle is to be a hunting rifle, I wouldn't lose any sleep over having a different cold bore POI provided that it does the same thing predictably and repeatably. You simply need to make note of it and adjust accordingly.

 

[Grumulkin]

The cold bore shot is, of course, the most important one while hunting but I can see why it would be irritating to have the impact point shift. I have a rifle that puts 2 or 3 in the right place before groups walk but that's a little easier t live with. With my rifle, it also doesn't shift the impact point as much as what you're having. Some observations:

1. I have a hard time believing that one, two or even 3 shots taken without barrel cool downs would be sufficient to heat a barrel enough to warp it. In my opinion, something else may be going on like perhaps heating of the bore making it slightly smaller which could mean higher pressure and velocity which would cause a lower group. If it is barrel heating and warping of the barrel, it's possible that cryo treatment of the barrel would help.

2. You say your groups are from a fouled barrel so I assume there is no oil in the barrel. Oil in a barrel will cause the first few shots to be high.

3. I doubt bedding is the issue but it could be that the barrel is pressing on the stock somewhere where it shouldn't be.