Odd Pressure Issue


Well-Known Member
Apr 11, 2009
Started doing load development this weekend and ran into a weird problem I hadn't really seen before.

The gun is an STW, Gre-Tan custom, neck turned 8mm brass to .310 in a .313 chamber, 168gr classic hunter hybrid jumping about .030, F215 primer, and retumbo powder.

I started out 1.0 gr below book minimum. 2 shots smoked the primer pocket and blew hot gas out past the side of the primer. Bolt lift was light and very easy. Not sticky in the least. 1 shot of the 4 barely left an ejector mark.

Now if this had happened and the bolt was the least bit heavy I'd understand but it wasn't. I've double and triple checked my powder thrower.

Wondering if this could be a bad batch of 215's?

You can see from the picture that one doesn't even have an ejector mark and the other 2 were smoked. All 4 were loaded identical.

Any help is appreciated.

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I wouldn't advise starting out below book MINIMUM. What you had is what I've found out the hard way about trying something light, especially in the larger cases like the STW. The minimums are there for a reason and I think you've stumbled on one of them ;)

I did the same thing with a 25-06 many years ago when I first started out. Scared the pee-diddly out of me.
Agreed... you can have ruptures/etc when the rifle is under loaded...
weird pressure peaks occur, primers rupture, etc happens....
There are "ranges" for a reason.
have you shot it over a chronograph? that will tell you a lot of info. also what does the case necks look like. how far down the neck is the smoke?

from what i learned on my lapua is that the books arnt always right for every gun. I was getting ejector marks no matter what i tryed but the bolt was still easy to lift. once i shot it over the chrono i figured out that i was shooting way faster than the books said i should, I am still working up a load but 2 grains under the lowest book value is still still gives me close to the upper end for speed for what they give on the max powder.

on the last 5 shots I was still getting a slight ejector mark and i was was loading to the book length, not sticking the bullet out, i ran them all over the chrono and there was 11 ft/sec deviation so i think im getting close. I was going to try droping it down 1 more grain and see if it still gives me as good of a group on paper and as good on the speed deviation. without an ejector mark.
I mis-spoke in my first post. I was only .5 gr below book minimum on my first try, not 1.0. I had 5 loaded at 73.5 gr. 4 of those I shot were in that picture I posted.

Well, I tried jumping into the Berger recommended range (74-78.1) per their manual last night. 75.5 gr of Retumbo. Same results. Completely destroyed 2 of the 5 cases I shot. Bolt lift was light on all 5. Very light half moons on 2 of the case heads from the ejector. My chronograph is a piece of schit, but it read from 3190-3217 over the 5 shots. That is wayyyy above the Berger book (3029fps @78.1gr), but....I don't put a lot of faith in the velo numbers from that book or my chronograph. It's proved it is good for showing accurate SD/ES numbers but the Avg is usually off. It's an old shoot through Chrony that is effected by the conditions.

I've triple checked my powder thrower. It's not the issue as best I can tell.

I've got a few left over CCI 250's from some reloading I did on a friends 30 Hart last summer. I'm going to try them tonight to see if I just got a bad batch of F215's.

I also used this same lot of 215's for reloading a 6.5 SAUM with a 130 VLD. It is a relatively low pressure round and guys are getting 10+ reloads in some cases with this round at 63.0gr of H1000. I inspected my box of 100 (about 20-30 of those are shot) and noticed this same issue (very very slightly, not as extreme) on 2 out of that lot.

I'm starting to think that the issue is the lot of primers. I'll be sure to post my results when I get to shoot again.
I suspect that's the source of your problem. NEVER load below minimum. Minimums, like maximums, in your reloading manual are published for a reason. Looks like you've discovered the messsage they're trying to convey.

Did you read the last post?
It looks to me like the primer pockets were enlarged. If it were just a pressure issue and the primers fit tightly then the primers would have been pierced where the firing pin struck. Gary
evening, did u contour ur primer pockets? all my cases get the primer pocket ream. I have RCBS prep station. I ran some 270 for a friend of mine. had 2 of the reloads due the same thing. I checked the fired cases and the primer pocket was undersized. sized the primer pockets. ran the same brass fired OK. I ran some 340Bee new brass the primer pockets were all undersized. when u seated the primers did the primer pockets have a good firm resistance?

food for thought

just countrylightbulb
I hope it's not a headspace issue. How would the headspace be causing this problem? Have you seen it before?

I'm not ruling it out but would be surprised if Greg Tannel messed that up. Plus, I've shot this rifle previously without the issue. Haven't shot it in quite some time but dusted it off the other day and started playing with the 168's because I had a ton of them and then this issue cropped up.

The primer pockets were only depth uniformed with a lyman prep center. I did not uniform them in diameter. They fit snug as you would expect from new brass.
Did you read the last post?

Yes, sir, I did read that last post. None of us can be sure what caused your specific problem. It could be lots of things, not the least of which might be enlarged primer pockets. The point I was trying to make there was that when the powder charge begins to burn the primer gets pushed back against the bolt face and everything in the chamber begins to swell. The case swells to fill the void provided by the head space which in turn pushes the base of the cartridge back against the bolt face and, essentially, reseals the primer. That all happens in an instant. If the charge is too small, even though the bullet may exit the barrel "normally", the pressures may not be great enough to maintain a seal on all the remaining cartridge components and pressure leakage past the primer is a possibility. I'd just hope that you don't get caught up in a post hoc ergo propter hoc scenario that leads to false assumptions.
In your situation I'd find some new brass, prepare loads somewhere in the mid range of the reloading manual recommendations, and try again.
I'll play here.... I've seen the same/similar thing with my old 7stw barrel.. One box of brass I had blew three primers on me with a known good load... I had a couple of issues with that rifle-- loose headspace was the big one but a crappy barrel/receiver fitment was a big problem too.

I looked at what the problem was after I lost rounds two and three; turns out it was used brass I had bought from a lgs to bolster my brass supply. Between the beat up brass and loose fitment with the super generous headspace, the primer really didn't stand a chance...

I would get your rifle over a decent chrono and see where you are really stepping out at. I would also do a load run up with another powder and check the things like brass length, neck thickness vs/ chamber width, etc. that could net you way more pressure than anticipated. Are you sure you are off .030" or might you be resting your bullet on the rifling??
Check everything and you will find your issue.... I'd bet you a wooden nickel it isn't the primer. The pierced primer is the effect of something else garfed up...
I think I'd stop putting more powder in this , until I came up with a reason for this thing blowing fire out of the wrong end. I see all the primers have the same markings stamped in them from the bolt. Is this existing pressure cutting, or is the bolt face that messed up. Since the gun has been sitting for a while , is the barrel rusted or pitted, is the powder correct , or has it been contaminated? If it were mine I'd send it to a good gunsmith and have it bore scoped, headspaced. If it all checked out , I'd start with new reloading supplies. k Redden
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