Primers 'pushed out'. Overpressure?

[ocabj]

I just inspected my once fired brass a little more closely for my 8mm Mauser reloads. I made 5 rounds each of 46.0, 46.5, and 47.0 gr H4895 an a 150gr Sierra SP (Hodgdon lists 50.0gr as max). The firing pin dent looks normal and the primers weren't flattened, but on closer inspection, it the primers are 'pushed out'. It looks like the primer came out of the pocket just a little on all the rounds, as if they weren't seated fully.

Is this a sign of overpressure? I'm pretty far under max, so I didn't expect to be overpressure with the loads. I've fired quite a few rounds of Turkish 8mm surplus in that rifle, and unfortunately, I don't have any of those once fired cases around to see if the primer pushed out of those too.

 

[P95Carry]

Fired thru Mauser yeah? Hmm .. well if bolt face fully on case base then primer should just set back to flush and not usually further.

If not flattened then seems like your pressures probably OK. Any pic's possible? Might help a tad.

 

[ocabj]

I'll take some pics tomorrow morning.

Yup. Fired through a Czech VZ24 purchased from Empire Arms.

 

[Zak Smith]

Pushed out primers can indicate low pressure loads. In this case, there is not enough pressure to push the case back to the bolt face, but enough to move the primer back.

If the primer pockets are getting larger, you've got an overpressure situation.

It could also mean excessive headspace.

-z

Edited to add:

American load data for 8x57JS is severely under the "European" or original spec. This is to avoid the liability problem if someone were to shoot the new larger diameter 8mm bullets in the older slightly smaller diameter bore. The loads I use in 8x57JS (using W748) are well beyond most U.S. data.

 

[P95Carry]

Zak .... excellent point indeed, re insufficient pressure. Tho looking at powder loads this does seem unlikely cos getting towards max - in theory.... and IIRC 4895 is not too fussy if loaded down a bit. Your ideas makes absolute sense tho for sure.... primer protrusion not cancelled out by set back against bolt sufficiently.

The head space aspect .... well again ... I almost mentioned that but seemed less likely .. but far from impossible ..... pic's still might help quite a bit. Even if headspacing not correct, I'd expect a fairly good degree of set back regardless.

 

[Zak Smith]

You could also buy a box of the new S&B 8x57 ammunition. It's loaded full-power.

-z

 

[ocabj]

Hmmm. I never thought too low a powder charge could have caused it. Something for me to think about.

 

[Zak Smith]

My full-power loads follow the data in the Hornady book closely- 55+ grains of Win748. Based on that data, 47gr of H4895 isn't very far off from max. This is curious.

-z

 

[30Cal]

My guess is that either you're setting the shoulder back too much when sizing or that the rifle has excessive headspace--in either case, you're cases are too short. In bad cases of either situation, the rifle may not go "BANG" every time you pull the trigger.

Ty

 

[Zak Smith]

If the rounds are overpressure, you should be seeing the webbing area of the case, just up from the rim where the width of the brass case goes from thick to thin, visually expand versus F.L. resized cases. You can see this in normal fired cases in .223 and 308.

Another sign to look for is "soot" around the case neck or on the case body. Soot on the case body indicates there was not enough pressure to seal the shoulder and gas came back around the case.

-z

 

[ocabj]

Took some pictures at work. Best I could do with bad lighting and no tripod. Hope the pictures are detailed enough.

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I just pulled 5 random cases from the 15 I loaded up and fired.

 

[Deavis]

ocabj:

Hmmm. I never thought too low a powder charge could have caused it. Something for me to think about.

This is actually a real pain if you are trying to salvage poorly loaded rounds. I missized some .357 SIG rounds and could not get them resized without unacceptable bullet setback. I removed the components and then set off all the primers before reloading.

Many of the primers came out far enough that it would hang up on my press because they hit the bottom of the shell plate. If you use a punch to set them off instead of the firing pin in a gun, they really come out.

Of course, now I realize that I could have just removed my decapping pin and resized them without a problem. Sigh... amateur reloading at its best. :banghead:

 

[sumpnz]

Didn't notice anything like this in the custom loads my FFL worked up for my Turkish Mauser. Can't remember off the top of my head which powder he used, but I know it was a charge of 52.0 grains, and we were chronographing velocities of 3006 fps (~15' from the muzzel) with the Hornady 150gr soft points. IIRC he was using Reminton brass, not sure about the primer. The primers were only just barely starting to show flattening at that load. The Turk surplus ammo would sometimes crater quite a bit so I'm sure this is a lower pressure load than that surplus ammo.

 

[Zak Smith]

ocabj,

A few questions.

1. Did you clean those cases at all before taking pictures?

2. Are you sure you seated the primers flush?

3. I hope you chrono'd these. What's the average velocity?

Those primers look really round, and I don't see much if any expansion in the web area.

I can't tell anything conclusive about headspace, and I also can't see enough detail on the case heads.

My guess is still underpressure.

-z

 

[Dave R]

My guess is a combination of underpressure and excessive headspace. But I could be wrong.

 

[ocabj]

1. Did you clean those cases at all before taking pictures?

2. Are you sure you seated the primers flush?

3. I hope you chrono'd these. What's the average velocity?

1. Nope. I didn't clean them.

2. The primers were seated flush, if not a little deeper than flush.

3. I did not chrono the loads. I will end up chronographing this weekend.

These are brand new Winchester brass and I did full length size them. Is it possible that I full length sized them too much, pushing the shoulder down a bit farther than I needed do? Would this cause this primer symptom?

 

[P95Carry]

Excellent pics considering ... thx. Sure shows this effect well.

Hmmm .. maybe we are still in same zone tho ..... lower pressure and/or headspacing . so damned hard to really know for sure.

Chrono figures would be interesting . and then relate those to full spec velocities etc.

Sorry no easy answer right now .... seemingly.

 

[Zak Smith]

Try the "Field expedient headspace test"-

Take a resized case, it chambers freely and the bolt closes easily.

Add one layer of masking tape to the base (trim around edges), the bolt should close with some force.

Add a second layer of masking tape, the bolt should not close.

You could also compare the base - shoulder dimensions of the new brass to new brass after your F.L. resize operation. If the die contacts the shellholder at full stroke, it should be set up right ?!

-z

 

[Dave R]

You can't "full-length resize too much". The dies are the SAAMI correct spec. If the headspace is excessive, then the correct die spec would be too "loose" for your loose chamber. The test Zak describes would tell you.

If headspace is excessive, a gunsmith can fix it for not too much money.

Or you could just neck-size your brass and let it stay at chamber dimentions.

 

[Sunray]

Bits of tape on a case head tells you nothing. Your loads are close to max but not over it. Get the head space checked before you do anything else. You may have to buy a set of guages as some smithy's won't have 'em for 8mm. Brownell's has guages for a reasonable price.

 

[Zak Smith]

The masking tape method can give you an indication of excessive headspace when proper headspace gauges are not available. That's what "field expedient" means, get it?

-z

 

[Jon Coppenbarger]

They looked better than a few of the ones that came out of my rifle on sunday at the 600 yard line. I knew they would be a little on the warm side for temps running over 100 or anything close.

It was really rocking and was starting to see soem signs of the load being to warm in my ar15 as the bolt was not locking back but have gotten used to that with warm loads at 600 yards.
I had a real wind change at around the 11th shot and left the round in the chamber a little longer than I wanted but had already pulled a few out and replaced them earlier and thought I was still in a good zone but it popped the primer and I knew it went into my rifle and in a ar15 it goes into the trigger group. I kept firing and low and behold the trigger froze up 3 shots later . I opened the rifle up and took my trusty dental pick I keep in the front of my shooting stool and just popped it out from under the trigger put it back together and kept firing, the last shot did the same thing.

I keep a extra set of rounds for days that it is to warm but had not blown any primers yet untill then and just had to be fast and carefull as I did not want to change loads toward the end of the string.
It was a hot , miserable switching windy day and that wind got me for a 8 and three 9's for a 195 at 600 yards.
I will make sure that I have enough of both loads before I shoot anymore matches in that weather.

 

[BluesBear]

Looks like underpressure loadings to me also.

Prime 2 or 3 cases and fire them. I'll wager the primers will set back the same way.

Your extractor isn't holding the case tightly against the bolt face which is not at all uncomon. In fact you don't want it to hold it too close or tightly.

Your ammo has just enough pressure to expand the case against the chamber walls for efficent gas seal but not enough pressure to over come this and push the case against the boltface.

Try the primer only test.

 

[ocabj]

Prime 2 or 3 cases and fire them. I'll wager the primers will set back the same way.

I fired two cases with the primer only and no powder or bullet just a few minutes ago. The result was that the primer was pushed out in the same manner as loaded cartridges, along with a dirty barrel. It's amazing how dirty primer residue is. I had to make a few passes with patches and Butch's Bore Shine to clean the bore again.

I did order a set of headspace gauges anyway last Tuesday. I didn't get them today which means they would be delivered tomorrow (USPS Priority), but tomorrow was declared a Federal holiday, so I won't get my 8mm Mauser gauges till Sat.

Thanks for the responses everyone.

 

[Big_R]

I'm pretty sure Bluesbear nailed it. Did you clean your brass before you took the pics? If there was soot back onto the shoulder, it supports the light pressure concept. A magnum primer may fix all of this (starting with minimum loads, of course).

Your headspace may or may not be long, and it really doesn't matter so long as you neck size. It is far cheaper to buy a neck size die than to shorten headspace.

Ryan