7mm PRC Pressure Signs?

TxLite

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Finally getting a chance to sit down and really look at some of the the brass from my 7mm PRC and trying to figure out what I’m looking at. This is all once fired factory ELDX in a carbon six Tikka prefit. None of these pieces have been run through a sizing die. No primers were blown, just decapped tonight. Several pieces have ejector marks. A few had sticky bolt lift. All pieces have a ring around them that appears to be the beginnings of case head separation. I ran a paper clip through several cases and cannot feel the ring from the inside. Is this overpressured factory ammo? Sloppy chamber? What am I looking at?9CBBC868-33EC-4FF6-B186-CEA0DD33EA97.jpeg3B5C4A33-6AD0-4AF6-A2B3-DBE31F005CCA.jpeg81EE613A-A2CC-4877-9ED4-6B63980EB921.jpeg
 

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TxLite

TxLite

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Lapua has 300 PRC. Can it be necked down?
It would be a little more extensive than that. The 7prc is quite a bit shorter than the 300prc. If it was feasible I’d use some of my ADG for the 300
 

Dos XX

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It would be a little more extensive than that. The 7prc is quite a bit shorter than the 300prc. If it was feasible I’d use some of my ADG for the 300
I did not know that. I thought it was necked down 300 PRC.
 

gbflyer

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If you’re getting an ejector mark like that you’re pushing up there pretty hot. Bolt cycling is shearing the brass off that flows back under pressure. That’s more than 60K. I’m surprised to see this with factory ammo. You won’t get many loadings out of those cases if that continues.
 

z987k

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If you’re getting an ejector mark like that you’re pushing up there pretty hot. Bolt cycling is shearing the brass off that flows back under pressure. That’s more than 60K. I’m surprised to see this with factory ammo. You won’t get many loadings out of those cases if that continues.
Max saami pressure is 65k. So, I'd imagine the factory loading is more than 60.
 

Mag_7s

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Hoping that’s what it is. Also hoping Alpha or ADG will release brass for it soon.
TxLite, ADG is supposed to be making brass for the 7PRC. I would also suspect the Hornady brass may be the problem, too soft in the wrong areas. What did the spent primers look like?
 
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TxLite

TxLite

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TxLite, ADG is supposed to be making brass for the 7PRC. I would also suspect the Hornady brass may be the problem, too soft in the wrong areas. What did the spent primers look like?
Primers had slight crater but nothing crazy. Edges were still rounded

Did you measure brass before and after?
.534 at the web, .518 at the shoulder/body junction. Ran through a sizing die and it hit .531 and .516

Edit to add: unfired was .529 at the web and .514 at the shoulder/body junction
 
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I have a 300 PRC I’m using Lapua brass in. I was getting the same results on my brass, very slight ejector mark and the same ring. I did not have a sticky bolt at all though. I hand load and this was happening with every load I tired starting at 5 grains under book max for the barrel break in loads.


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TxLite

TxLite

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I have a 300 PRC I’m using Lapua brass in. I was getting the same results on my brass, very slight ejector mark and the same ring. I did not have a sticky bolt at all though. I hand load and this was happening with every load I tired starting at 5 grains under book max for the barrel break in loads.
I had sticky bolt lift at first. It went away after a few rounds. I attributed it to the new rifle breaking in with seemingly hot factory ammo. For clarification, were you getting the ring on your Lapua or Hornady brass? I haven’t noticed them on my ADG in 300prc until after running them through the sizing die
 
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I had sticky bolt lift at first. It went away after a few rounds. I attributed it to the new rifle breaking in with seemingly hot factory ammo. For clarification, were you getting the ring on your Lapua or Hornady brass? I haven’t noticed them on my ADG in 300prc until after running them through the sizing die

I am using all Lapua brass, no Hornady.


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Primers had slight crater but nothing crazy. Edges were still rounded


.534 at the web, .518 at the shoulder/body junction. Ran through a sizing die and it hit .531 and .516

Edit to add: unfired was .529 at the web and .514 at the shoulder/body junction

That's a bummer there's that much expansion at the web! Seems like you're already into clicker territory with that brass just off the factory firing. I wouldn't be surprised if it will be prone to sticky extraction on every firing forward now.

Did you get velocities on it? Be interesting to see if it gets a little better with break in.
 
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I had no idea. I guess they have to do something to get it to stand above the other 7 mags.
Pretty much every new cartridge besides the AR specific ones i've looked at starting with the WSM/SAUM/RUM families has been 62k-65k SAAMI max pressure with most being 65k. That includes weatherby 6.5-300 and 6.5 RPM, creedmoors, PRCs, 6GT, noslers, etc. So it's not like they are doing anything different.
 
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TxLite

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That's a bummer there's that much expansion at the web! Seems like you're already into clicker territory with that brass just off the factory firing. I wouldn't be surprised if it will be prone to sticky extraction on every firing forward now.

Did you get velocities on it? Be interesting to see if it gets a little better with break in.
Yeah I averaged 2748. Barrel is 18”. I noticed the sticky bolt lift and some of the ejector marks that day didn’t acknowledge the rings until I sat down yesterday to start evaluating and prepping brass for 175 EH’s.

 

gbflyer

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Pretty much every new cartridge besides the AR specific ones i've looked at starting with the WSM/SAUM/RUM families has been 62k-65k SAAMI max pressure with most being 65k. That includes weatherby 6.5-300 and 6.5 RPM, creedmoors, PRCs, 6GT, noslers, etc. So it's not like they are doing anything different.

Good to know. I dwell in the dark ages with my cartridge selection. Still a 300 H&H man. Haha.
 
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