Thread: My 7mm PRC is driving me nuts…

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.

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.

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

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.

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 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

Originally Posted by No.3

Random question, is the barrel fully secured into the action? No chance of anything moving mechanically? Suppressor is fully locked in, no wiggle at all? Is the barrel fluted, fully stress relieved and everything true in line? Bolt nose fitting the chamber end of the barrel, nothing weird there? Screws all clear of the bolt inside the receiver? Recoil lug not moving in the stock and receiver recess?

Something will be causing this, but finding it can be a mission.

Good point, will get barrel off and back on and re torqued, can’t hurt to try

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

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.

Looks like the only thing left is try a different projectile, there’s a box of 168 vlds on tm at the moment. If you can’t get something else shooting it looks like tentman might have identified the last option. Worth trying a different projectile though I reckon.

Maybe the " prc dream" is over. Meanwhile a little 7 mm rem mag waits🙂

I had the same issues with a 7mm saum some years ago same barrel but a carbon one.
I spent ages trying different powder and bullet combos in the end I listed it on here and told of all the issues I had and moved on to a factory Sako no more issues.

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Maybe your barrel shoots better at 2990fps and not at 2900. Try a lighter projectile at near 3k fps. Or push those same pills you were using back up to 2990fps with a different powder as you said you were using a fairly fast burn rate powder.
I have a 6cm that was shooting great at 3050fps but the load was too hot. Backed off to 2920fps and it shot poorly in comparison. I changed powder to get it back over 3k fps and also tried a different pill @3100fps and it was shooting great again. Clearly my barrel has better harmonics at over 3k fps. Your barrel could be similar .