Thread: My 7mm PRC is driving me nuts…

I’m no help here at all, but a we plug for Hardy. I built a 20inch featherweight 7-08 on a sako 85 action with a kroceg stock with a Hardy barrel and it’s a half moa rifle. Wasn’t keen on a Hardy but the guy who built it was and he knows his stuff so I trusted his opinion. I think that’s a pretty good result for a lite weight and I’m happy.

Another question. If your initial load was well over pressure, is it possible some part of the action has become fatigued and changed after 500 over pressure rounds? Same with the barrel. I have no knowledge on the possibility, others probably will.

Originally Posted by Mararoa

Another question. If your initial load was well over pressure, is it possible some part of the action has become fatigued and changed after 500 over pressure rounds? Same with the barrel. I have no knowledge on the possibility, others probably will.

You have a good point. Tikka action are known to be pretty strong and I never got hard bolt lift so you would assume receiver is ok. I’m kind of getting to the conclusion the barrel lost accuracy.

I’d ditch the barrel and start again, get a true flight one or one from offshore.

I have one hardy barrel, it doesn’t shoot as well as I thought it should ( it’s ok but both my trueflights are mint shooters) and it copper fouled really bad at the start.

My mate had virtually the same issue as you describe. He pretty much shot out his first barrel chasing his tail, initially shot .2-.3 reliably then started getting groups like you. The chassis had been skim bedded and instead of holding everything in place the action was moving which eventually after a few hundred rounds you could see witness marks in the bedding. Removed bedding and it shot fine again until his barrel was shot out a 100 or so shots later. His was a 7saum.
The other thing I’d look at is the projectiles, I’ve never bothered weight sorting projectiles but I have done some weight sampling occasionally, I’ve seen a few posts claiming that hornady qc has dropped, maybe weigh and measure a few to see how consistent they are.

Originally Posted by Plinky

My mate had virtually the same issue as you describe. He pretty much shot out his first barrel chasing his tail, initially shot .2-.3 reliably then started getting groups like you. The chassis had been skim bedded and instead of holding everything in place the action was moving which eventually after a few hundred rounds you could see witness marks in the bedding. Removed bedding and it shot fine again until his barrel was shot out a 100 or so shots later. His was a 7saum.
The other thing I’d look at is the projectiles, I’ve never bothered weight sorting projectiles but I have done some weight sampling occasionally, I’ve seen a few posts claiming that hornady qc has dropped, maybe weigh and measure a few to see how consistent they are.

Could be projectile. You would think you sometime get some group without the issue though. I would be keen to test the Berger 175 elite hunter but they hard to find at the moment

Yep I had split groups trying to get some eldx in a different calibre to group, never could. Have a very close look at your skim bedding and see if it’s been buffed shiny from small movement.

Originally Posted by Plinky

Yep I had split groups trying to get some eldx in a different calibre to group, never could. Have a very close look at your skim bedding and see if it’s been buffed shiny from small movement.

Thanks skim bedding all good, tested on another Tikka also all good. And tested the 7prc in another stock as well, same deal

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

It is never throwing shot in the same order, sometime the first shot is out of the group. I did the test waiting for the barrel to cool down and was still getting split group, plus on some group I was less accurate as breaking position.

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.

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.

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?

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.

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?