Blown Primers?

[Walkstoomuch]

My wife has a Christensen Mesa in 6.5cm with a CGS Hyperion K suppressor that she was shooting yesterday at the range. She shot 5 rounds with her preferred hunting round (factory Nosler 140 grain Accubond Trophy Grade) to check zero for her upcoming early season cow tag. She then switched to shooting factory Nosler 120 grain ballistic tip bullets. She took maybe 10 shots, during these shots she had one misfire. Then she decided to switch to shooting another rifle and I went to put the rifle in the case as she was done with it for the day. When she handed me the rifle we heard a rattle and we shook out two primers that were somewhere in the rifle. I called my gunsmith and he said sometimes that happens and perhaps the barrel is dirty and that could be causing higher pressures. The rifle was clean before shooting and when I got home ran some Butchs Bore Shine through it as he suggested to make sure there wasn't excessive copper fouling, he said this would show as heavy blue coloring on patches. There was some blue but not what I've seen on other rifles when cleaning. I have very little knowledge and hope someone can tell me it is perhaps just a bad batch of ammo or something larger at play I should be looking at. Thanks

 

[Osteodoc08]

Have you shoot that ammo without the suppressor before? Any other signs of high pressure including swipe marks on the head stamp or stiff bolt lift? This was factory ammo?

 

[sndmn11]

Which cases did the primers come from?

 

[Walkstoomuch]

The primers came from the ballistic tip ammo.

Both ammos are factory produced Nosler

She did mention the bolt being difficult to lift at one point and we assumed it was user error or needing some oil

I have shot the rifle without the suppressor many times, also with the suppressor. However I don't think we've shot that specific ammo, it was something I found during the pandemic and swiped it up for range practice as ammo was scarce

Not sure about swipe marks as I didn't keep any of the brass or inspect it while we were there. I now know to do this in the future

 

[Osteodoc08]

Sounds overpressure. Did you buy the ammo commercially or off someone? If purchased commercially I’d stop shooting it, call Nosler and provide them sku and lot number. If bought off someone, I’d trash it.

 

[Osteodoc08]

I’ve had primers blow when leaning hard on brass with a few too many reloads on them, but never US made ammo.

Had a good friend of mine but some AMMO, Inc ammo cheap and had some seriously overpressure

 

[Walkstoomuch]

I bought it from my local Sportmans Warehouse. I'll reach out to Nosler. Thank you for your help.

 

[Dented]

Can you follow up with us after you talk to Nosler? Thanks!

 

[kevin11mee]

Sounds like too much pressure. Possibly carbon build up on the throat of the rifle? How many rounds through it?

 

[Walkstoomuch]

The rifle probably has around 300 rounds though it. How would I determine if there is carbon buildup on the throat? I use a bore guide when cleaning, does this keep me from thoroughly cleaning the throat? I ordered some long cotton swabs to get around the front of the chamber as this is blocked with the bore guide.

I'll post any info I get from Nosler

 

[ScreamingPotato]

I experienced this with a 270 WSM shooting factory ammo. We cleaned the everloving fecal matter out of it, and cleaned it again and again and the problem went away.

 

[kevin11mee]

The rifle probably has around 300 rounds though it. How would I determine if there is carbon buildup on the throat? I use a bore guide when cleaning, does this keep me from thoroughly cleaning the throat? I ordered some long cotton swabs to get around the front of the chamber as this is blocked with the bore guide.

I'll post any info I get from Nosler

A borescope will tell you for sure. However, you can simply clean the throat without a borescope and see if it helps with pressure. If you have an old cleaning rod that you can cut and attach to a hand drill, it will work better. Get a .30 cal nylon brush and wrap a cleaning patch around it. Apply carbon/copper remover to the brush/patch. Insert into the throat area (where the bullet leaves the case) and spin the drill. Let it soak for a while and use dry patches to clean.

 

[Walkstoomuch]

Would I do this process with the bore guide installed?

 

[Wapiti1]

Would I do this process with the bore guide installed?

No. There are a couple of ways to get at it. My preferred method is to plug the throat with a tight patch, and pour in Kroil or ATF. Let it soak for a few hours and then scrub with a bronze brush.

Jeremy

 

[kevin11mee]

Would I do this process with the bore guide installed?

I do it without

 

[TaperPin]

That does seem puzzling.

Removing the carbon ring is a good thing to sort out.

Christensen is known for exceptional accuracy - their chambers are probably cut with reamers on the small side of SAAMI specs, which might magnify a small pressure issue.

Some lots of factory ammo can be pretty hot, and some brass is a little soft and does strange things with normal pressure. If the primers were flattened out a normal amount I‘d guess the brass was just a little soft (or the primers were slightly undersize) Likewise if the primers were really flat with some flow around the firing pin indentation that would be consistent with high pressures - or soft primer cups.

It can also be an issue when a cartridge is allowed to sit in the chamber of a hot barrel a few minutes and soak up barrel heat, or the cartridges were sitting out in direct sun on a hot day.

The good news is your elk hunt will be at cooler temps so pressures will be lower than on your range day.

Hopefully its a fluke and works itself out.