Thread: My 7mm PRC is driving me nuts…

Originally Posted by Tentman

Local gun shop has two buggered Tikka actions with lug setback from being run "too hot". They are not "bullet proof" particularly with magnum cartridges that produce higher bolt thrust. Lug setback = inconsistent headspace = inconsistent ignition.

Is there anyway to check that or only a gunsmith can tell?

I had a similar problem.

Something is moving. In my opinion your split groups are too consistent for it to be the barrel.

I would suggest measuring the external dimensions of your action and bottom metal to see if they are undersized and moving in the stock?

Originally Posted by norsk

I had a similar problem.

Something is moving. In my opinion your split groups are too consistent for it to be the barrel.

I would suggest measuring the external dimensions of your action and bottom metal to see if they are undersized and moving in the stock?

That’s what I thought too! I tried different stock and chassis and skim bedded a chassis. I don’t see any marks on the bedding job, the receiver moving would leave marks I assum

Originally Posted by tibo

That’s what I thought too! I tried different stock and chassis and skim bedded a chassis. I don’t see any marks on the bedding job, the receiver moving would leave marks I assum

Get the vernier calipers out and measure everything.

You might have skipped the reason ?

I had similar results with my 300 and both 225 and 208gn ELDMs. Changing powders didn’t help.

Switched projectile type and had instant velocity gain and grouping consistency.

I can’t explain why it shot well for you initially but it’s worth a try loading up something like a Sierra, Berger blah blah.

Get someone who is a good / known shooter to shoot some groups.
I don’t like to admit it , but I’m the biggest variable when it comes to accuracy with my Rifles.
I’m not trying to be a Smart Arse , but make sure that you have eliminated yourself from the equation.
I’ve had similar problems in the past and nearly pulled my hair out trying to solve the problem , mine was a damaged muzzle crown that wasn’t obvious, but was the cause of much drama.

Originally Posted by distant stalker

If it will shoot tight group as a series of single shots with cooling in between it could suggest heat related pattern which may point in the direction of what Mararoa is suggesting. Does require really consistent shot setup etc but about the only thing you don't seem to have tested so far if I have read correctly

This comment touches on something that doesn't seem to be given enough consideration in cases like this. When metals are heavily worked, as in barrel manufacturing, there is substantial stress introduced, so much so that I often wonder at a barrels ability to resist bending like a banana when exposed to work as in a projectile screening down the bore. To me it is not at all surprising when a comparatively thin sectioned steel tube reacts by bending after a few rounds only to return to its happier state once allowed to cool. The fact that it once didn't seemingly react in the same manner is also not at all surprising.

Originally Posted by Ground Control

Get someone who is a good / known shooter to shoot some groups.
I don’t like to admit it , but I’m the biggest variable when it comes to accuracy with my Rifles.
I’m not trying to be a Smart Arse , but make sure that you have eliminated yourself from the equation.
I’ve had similar problems in the past and nearly pulled my hair out trying to solve the problem , mine was a damaged muzzle crown that wasn’t obvious, but was the cause of much drama.

No offense taken I have eliminated myself from the equation

Originally Posted by Tentman

Local gun shop has two buggered Tikka actions with lug setback from being run "too hot". They are not "bullet proof" particularly with magnum cartridges that produce higher bolt thrust. Lug setback = inconsistent headspace = inconsistent ignition.

Been thinking about this, I would have experienced hard bolt lift wouldn’t I? Never been the case. Inconsistent ignition would also mean my SD would be up?

Originally Posted by tibo

Been thinking about this, I would have experienced hard bolt lift wouldn’t I? Never been the case. Inconsistent ignition would also mean my SD would be up?

I would have thought so but it's easily checked and eliminated, a borescope will see it.

Originally Posted by tibo

Is there anyway to check that or only a gunsmith can tell?

This would create a headspace issue as mentioned, I think you would notice it being a precision reloader.

Yes didn’t notice any headspace inconsistencies and didn’t see anything anormal on bore scope.

Few last things I will test:
-fresh adg brass.
-Retorque barrel just in case. Maybe pull it and refit, retorque
-could try other projectile, this batch of 180 eldm was shooting great though, inconsistency within batch could still happen I guess. Will measure and weight a few for the sake of it.

how about uneven bolt lug contact. Other than that just get a 6.5x55

Another thing to check, do the action screws have plenty of clearance in the stock, if they are "tight" due to bedding compound getting down the holes then they are acting as recoil lugs and that ain't good.

What stock is it? Really snotty cartridges can cause the stock sidewalls to flex enough to cause accuracy issues ( Mauser sporters often had "side panels" on the stocks for this reason). If it's an alloy chassis maybe it has developed a crack?

Another thought. If you've kept targets from earlier testing try super-imposing them. Our brains play funny tricks and many a time I've shot several good 3-5 shot group, yay sub MOA. However if you look at several lots of groups with something like BallisticX it can be a bit disappointing. . . .