Problem with first shot of every group

[Bob C]

I had a .300 Win. Mag. barrel which put it's first shot of the session 8 MOA high, and then within four rounds settled down and did MOA groups. Bedding and fore end changes never helped, and I sent the barrel back to T/C, and they replaced it.

I tried the new barrel a couple of weeks ago, and it did fine. Groups were around 1.5 MOA, which seemed to indicate some potential.

Today, the barrel put the first round of every group three inches high at 100 yards, with the next two into an inch or so, but three inches down from the first round.

It did this on the first group, with the first round from a clean cold barrel, and then did it on the next seven groups. After one such group, I just continued firing without any delay, on a different aiming point, and got a nice three shot group of 1.25"  I had fired six rounds in less than four minutes. I waited two minutes by my watch, and fired another three shot group. The barrel was still hot.  It went back to the same pattern as before, one high then two in an inch.

I was shooting from a sandbag, and was VERY careful not to shift position. All of the scope mount and base screws were tight. The fore end is a Virgin Valley, with their hanger bar  on the barrel.

I have two other barrels that don't have this problem.

By this starting rather suddenly, I thought it might be the scope. Any  ideas or suggestions will be much appreciated.

[oneshotonekill]

What kind of rings are you using?  It sounds like the rings may be slipping on the base upon the first shot then staying in place until you set the gun down and start over.  Make sure the rings are securely attached to the base, and push them to the front of the cross slot when you tighten them, this way the ring is supported during recoil (due to the contact with the front of the slot in the base) and there is less chance of the rings slipping.  This is assuming you are using some type of weaver style rings.  Other than that I'm stumped since it happens if the barrel is hot or cold, clean or fouled.

[Bob C]

I mounted a different scope and today I went back to the range.

With four rounds, I was more or less sighted in, and there was no sign of stringing. the POI followed the adjustments nicely. I then let the barrel cool for about fifteen minutes before firing my first groups ( three shots at 100 yards).

1st group:    .4"
2nd group    .9"
3rd group    2.0" ( but round).

I thought I had found the problem.

Then I waited a few minutes, and began firing again. The stringing came back, but not as bad as before.  Groups ran close to  2" average. For three groups of four rounds each, not counting the first round, I got a 1.25" average for the last three rounds.

Then I tried someone's suggestion and loosened the rear screw on the hanger bar. This helped quite a bit.  Groups were around 1.5".  I also tried tightening the screw, with a paper shim between the hanger bar and the barrel, and that didn't help as much.

My current theory is that there was a problem with the scope, and that there is also a problem with the difference in thermal expansion between the hanger bar and the barrel.

[oneshotonekill]

My current theory is that there was a problem with the scope, and that there is also a problem with the difference in thermal expansion between the hanger bar and the barrel.

Bob if you fired 13 rounds (4 to sight in and 3 groups @ 3 shots) then waited a few min and began shooting again on a 85+ degree day then experienced stringing I would think it is definately heat related.  As warm as it was in SE PA today 13 shots of 300 win mag would get a barrel mighty hot and a few min will not allow it to cool.  When I'm playing with heat issues and shooting in this weather I fire a few rounds then put that gun in the truck with the A/C on full blast while I shoot something else.  By rotating the guns thru the A/C I can keep them cool enough, and it gives me an excuse to shoot more of my guns.  Where are you located in SE PA?

[Redhawk1]

I would have to agree with oneshotonekill, I think heat is a lot of your problem. JMHO.