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Sudden accuracy issues - 6.5 PRC

clark33

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Mar 2, 2019
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I have a custom built 6.5 prc. From day one it has shot Hornady match 147 very well. Usually in the .5 MOA range. It has served me well for a few hunting seasons.

I am around the 500 give or take a few round count. Started shooting it again late august and noticed immediately something was off. I have checked all screws/torque. Tried a NX8 and Bushnell LRTS and two different sets of ARC rings. With both scopes, rings, pre cleaning, post cleaning, re-torquing it is shooting 2 MOA at best.

My average velocity was 3017 fps before. Chrono’d it last week and it was 2973 fps. I just don’t know if the barrel went south earlier than expected. If Hornady changed something in their match ammo, or if there is something else wrong with the rifle to cause this. I usually clean every 80-120 rounds and after every hunting season when it’s been out in the elements. I only use bore tech eliminator and a nylon brush with bore guide.

Last fall group:

82D81551-20D8-4E9F-AFEE-95FA3E621F70.jpeg



This fall group:
9D13C261-FA50-493C-8FB6-74DF079A3B4C.jpeg
 
So the very last time you shot it a few months ago it drilled? And now after sitting for a while it got all sloppy? I guess the basis of my question is are you certain it suddenly got bad? Not a gradual thing that went unnoticed?
 
We had a 300 Norma a few years ago that hammered for 200-250 rounds and went south. I had cleaned it several times trying to figure it out. The gunsmith suggested cleaning until no copper was visible at the muzzle. It took forever but once the copper was gone accuracy returned. That was the first time I had ever seen copper cause issues. We have gotten a borescope since then and I can’t imagine not having one. It saved me huge headaches a couple of times since then.
 
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6.5PRC is hard on barrels. No way around it. I’ve seen barrels puke in just under 500 rounds and go no more than say 900. That’s about tops….900 rounds. So 500 to 900 is with our barrels. Button rifled barrels are typically less in terms of barrel life.

I’ve also seen button barrels where the shooter got it so hot that the barrel basically relieved itself and the bore opened up (went sour).

The velocity loss if that is the same lot of ammo as before is a warning sign that the barrel could be gone.

If it’s a different lot of ammo a velocity swing of 44fps then could mean nothing.

How does the barrel clean and or foul during shooting?

Rate of fire, rounds in between cleanings, type of powder…. All variables as well.

Try a different scope to rule that out?

Any damage to the barrel from cleaning or storage?

More questions than answers right now. Need more info.

Later, Frank
Bartlein Barrels
 
We had a 300 Norma a few years ago that hammered for 200-250 rounds and went south. I had cleaned it several times trying to figure it out. The gunsmith suggested cleaning until no copper was visible at the muzzle. It took forever but once the copper was gone accuracy returned. That was the first time I had ever seen copper cause issues. We have gotten a borescope since then and I can’t imagine not having one. It saved me huge headaches a couple of times since then.
300 Norma is another hot barrel burner as well.

If the copper is building up on tops of the lands….that is usually an accuracy killer.

Did you switch from solid bullets to conventional jacketed bullets or vice versa? That can cause issues also.
 
Different lot of ammo, the boxes I have on hand now are newer lots.

The barrel is a carbon wrapped Benchmark barrel

In the past, following bore techs cleaning instructions (3-4 wet patches, 10-15 strokes with wet nylon brush, 3-4 wet patches then let sit, dry patches last) I would get clean dry patches relatively quick. After 2-4 clean bore shots the accuracy would settle right back in.

A typical range session would be anywhere from 1-5 shot strings then I'd shoot my 6 creed and let it cool, I basically would alternate between rifles but a lot of trips with 6.5 PRC were just to confirm data/dope after purchasing a new box of hornady match (I hunt with the match ammo).

I have tried a NX8 and a Bushnell LRTS and 2 different sets of ARC rings.

It is stored in a cool dry environment and I am not sure if I damaged it cleaning, I use a bore guide, dewey rod, bore tech patches on a jag and a bore tech nylon brush. I also have a chamber mop/brush I use real quick after taking the bore guide out to make sure no solvent gets left in the chamber.

I did try a test load from McCourt (FCS) and I contacted him this week asking if he could load me up a batch of the ammo that shot the best during testing. If that ammo is all over the place I will definitely know something is up.
 
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If it's a different lot of ammo that is one thing to look at for sure.

Also even though you've cleaned it....the 6.5PRC along with other calibers produce a lot of carbon fouling. If you have a real heavy carbon build up you might have to clean the bore with some JB Borecompound (blue label not the red label). This could be causing the accuracy issue also.

I've also seen 6.5PRC and similar calibers where the carbon fouling was so bad that the only thing we could do to help get the accuracy back was to finish lap the barrel again after cleaning it. I don' recommend you finish lap it yourself if you don't have the proper equipment/tools to do it.

1664380014032.png
 
Don't use a brush with any type of an abrasive! Guaranteed to cause bore damage.

Use the JB on a snug fitting patch only.

Also you didn't put the gun away dirty for an extended period of time did you? If you put the guns away dirty....the fouling in the barrel can also cause pitting/damage to the bore.

Later, Frank
 
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I did try a test load from McCourt (FCS) and I contacted him this week asking if he could load me up a batch of the ammo that shot the best during testing. If that ammo is all over the place I will definitely know something is up.
One of the guys here built a hunting rifle a couple of years ago in 6.5PRC as well. All of a sudden he noticed the accuracy wasn't great. No where near a round count that the barrel should be junk.

He had me look at it and I said it's the amount of carbon fouling you have in it. So we cleaned it really good and gave the bore a light finish lap. Got about 90-95% of the carbon out. Accuracy came right back.
 
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Different lot of ammo, the boxes I have on hand now are newer lots.

The barrel is a carbon wrapped Benchmark barrel

In the past, following bore techs cleaning instructions (3-4 wet patches, 10-15 strokes with wet nylon brush, 3-4 wet patches then let sit, dry patches last) I would get clean dry patches relatively quick. After 2-4 clean bore shots the accuracy would settle right back in.

A typical range session would be anywhere from 1-5 shot strings then I'd shoot my 6 creed and let it cool, I basically would alternate between rifles but a lot of trips with 6.5 PRC were just to confirm data/dope after purchasing a new box of hornady match (I hunt with the match ammo).

I have tried a NX8 and a Bushnell LRTS and 2 different sets of ARC rings.

It is stored in a cool dry environment and I am not sure if I damaged it cleaning, I use a bore guide, dewey rod, bore tech patches on a jag and a bore tech nylon brush. I also have a chamber mop/brush I use real quick after taking the bore guide out to make sure no solvent gets left in the chamber.

I did try a test load from McCourt (FCS) and I contacted him this week asking if he could load me up a batch of the ammo that shot the best during testing. If that ammo is all over the place I will definitely know something is up.
Shine a flashlight at the end of your barrel and see if you can see copper in the rifling. I used to clean exactly like you’re saying until this happened. It literally took hours to get all of the copper out and then accuracy returned. I don’t always clean for hours by any means but anytime I have an accuracy issue the first thing I do is clean every trace of copper out of the barrel.

Borescopes are really cheap these days you should grab one. They can be really helpful in diagnosing things like this. I had a 6.5 CM barrel that turned to crap and without a borescope I would have never found the huge glob of copper at the gas port. I had to soak a wet patch on the copper overnight to get it out. There is zero chance I would have ever fixed that barrel if I didn’t have a borescope.
 
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If it went from hammer to shotgun pattern from one range session to another it’s either fouling, your new lot of ammo, or both. Yes your barrel is at about the round count a PRC will Peter out, but it doesn’t just go from .5moa or 2moa like that, it’s gradual.

I would clean the fuck out of if with boretech eliminator and also get some different ammo to try. Maybe try to find a couple boxes of different types of Berger ammo, it’s a lot more consistent than Hornady.
 
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Got a batch of custom loads coming from McCourt munitions, if that doesn’t shoot then I’ll know for sure.

Got it clean clean this week and went out a day ago, groups improved to 1.5 moa but still not near what it has consistently been the last few years
 
I have a friend who just got a hold of me, he has a 6.5PRC, carbon6 prefit on a defiance action, xlr element chassis. He had always shot the 6.5PRC hornady match. Well today he took it out with some newer hornady lot ammo and said he was having it jump left and right at distance. He thought he need to retorque everything, but it sounds eerily familiar.

Has anyone else been having issues with hornadys newer lot of match 6.5PRC?