• Watch Out for Scammers!

    We've now added a color code for all accounts. Orange accounts are new members, Blue are full members, and Green are Supporters. If you get a message about a sale from an orange account, make sure you pay attention before sending any money!

First Blown Primer

RmeJu

Sergeant of the Hide
Full Member
Minuteman
Apr 23, 2019
156
41
Well, I can't say I'm proud of this, but I wanted to post it to help others and myself learn from it. The offending load recipe was:

Cal: 7mm RM
Bullet: 184gr Berger F-Open
Charge: 70.7gr VV N570
Jump: .010"-.012" off the lands
Other: Nosler brass; Win LRM primer; 28" 1:8.5 twist bbl

I was fine tuning this load a few days ago, and blew my first primer. I was testing three loads in two nodes that showed promise from a few weeks ago--the one listed above, a slightly heavier (70.9gr) variant, along with a lower node using 60.9 gr of N570. None of the rounds showed pressure signs that I could see (nor did slightly heavier charges I tried in the earlier test round). However, the original test was done in ~75* weather, whereas the one from a few days ago was done in ~95* weather (although under cover, out of direct sunlight). The headstamps of the 20 rounds in question are pictured below, although I obviously didn't fire the last two after the primer blew on #18.

20200703_173408.jpg


As you can see in the picture, the one that blew has a clear ejector mark, but none of the previous 17 rounds did. On the one or two before it, I thought I felt some stickiness in the bolt lift, but I wasn't sure if it was my imagination, since I hadn't had any trouble with this load up to this point, or with a couple of test loads that were a little bit heavier. I also didn't see anything on the case head indicating I should stop. The one that blew was #48 fired that day. For what it's worth, I had been using a home made barrel cooler between each 5 shot string to manage the heat buildup, and shooting the three loads being tested round robin.

Here is a picture of the bolt face after the shot:

20200704_123127.jpg
20200707_211826.jpg


I got the load recipe from Berger over the phone, since there isn't data published for the 184gr F-Open bullets yet. Naturally, they cautioned that I should watch for pressure signs, which I thought I was doing, but apparently not. To my admittedly untrained eye, it doesn't look like I damaged the bolt face, but I'd appreciate a second opinion. As for the brass,
I'm assuming that I should trash the brass with the blown primer, even if the pocket would still hold one(?), and maybe the others as well(?)

Maybe it was just the extra 20* of heat that got me that day. Thanks for any advice, and hopefully others can learn from my mistake!
 
Last edited:
The plan was to start out .010 so that when I started testing various seating depths (.030, .050, .070, .090, and .110) the initial test loads would already have the worst pressure, rather than starting deep and working my way closer to the lands. That's the way I read to do it anyway, but maybe I'll back off more to start in the future.
 
  • Like
Reactions: spife7980
Your way would have induced heavy bolt lift and ejector marks. A better way is to start .050” off and that way you won’t blow primers. Then you have room to maneuver.
Clean the bolt face to see if there is any pitting. We can’t tell from the pics.
 
Were your primers seated properly? I only ask because the ones in the lower right of the picture are canted and a couple look to have two small leakage lines from them. And the third row second from the bottom appears to have a mark on it over the L. Could just be the lighting in the pic.
 
It blew your bolt around to the wrong side. I'd throw the rifle away.

A small variation in bullet shape could make the difference between 12 tho off and in the rifling.
 
Could it be the primer it’s self? I know Winchester primers run a little on the small side. How did the primers feel when seating them?
I only ask because I have had issues with nosler 308 brass and Winchester primers. After a couple firings they seat very easily, almost too easy. I switch to cci200 and haven’t had an issue.
Just a thought.
 
  • Like
Reactions: IronOperator87
Could be a variation in that bullet or possibly that case has less volume from construction or it’s a bit harder and didn’t size down as much as the others.

Doesn’t pay to load to the edge of pressure.


You could try some more jump with it
 
  • Like
Reactions: isofahunter
Good morning,

Had to switch from Winchester primers after LR primers failed and gas cut a bolt face, and had the same thing happen on a different rifle with Win LRM primers the week after. Will never use WIn primers again, even though Winchester did make it right and repaired both rifles and bought back the rest of the Win primers in my possession. The return and repair process took months, but I ended up NEEDING to buy a new rifle for hunting that year. :cool:

Aaron
 
The bad win primers I had several years ago just blew a pinhole in the corner of the cup. It looks like the OP's blown primer fell out of the pocket. Very different situation.
 
  • Like
Reactions: Spicerack
The bad win primers I had several years ago just blew a pinhole in the corner of the cup. It looks like the OP's blown primer fell out of the pocket. Very different situation.

You are right, and I should have mentioned the mode of failure with the pin hole at the corner of the cup... mine failed this way too.
 
Clean the bolt face to see if there is any pitting. We can’t tell from the pics.

Here you go. Also fixed OP.

20200707_211826.jpg


Could be a variation in that bullet or possibly that case has less volume from construction or it’s a bit harder and didn’t size down as much as the others.

I guess I can't disagree with those possibilities, although I kinda thought that the heat was likely a (or the) significant factor here. Am I misreading that?

Doesn’t pay to load to the edge of pressure.

You could try some more jump with it

I might do that, maybe start out at .040 and .020 intervals up to .120. I liked how this load was performing, so I was hoping to give it a try. I may just run with the lower node though. It was holding up too.

You are right, and I should have mentioned the mode of failure with the pin hole at the corner of the cup... mine failed this way too.

Does this mean that you don't think it was my primers, since I have a different failure than you did?
 
Your primers look kind of flat, not super flat, but more so than I usually see on factory ammunition. Also, it looks like you have some cratering in the case in the lower left corner.
 
Does this mean that you don't think it was my primers, since I have a different failure than you did?
[/QUOTE]

I'm no expert to make that determination, but here's a pic of one of my failures and you can compare and try to determine that difference. Also a pic of gas cut bolt face. Mine were mild loads well within published load data with SAAMI spec COALs.

IMG_20170319_153338239.jpg

IMG_20170319_153514542.jpg