what might cause this....

[joseph-98]

this is out of my 300 blackout..... this brass is 4-5 times fired ... this is stamped 300 blackout brass... my load looked like this

h110 18gr
147gr m80
sm rifle primes
2.2 col
this is out of a 16 inch ar15

I used 15 gr of h110 and the next round would never get picked up... at 18.5 it was leaving extractor marks on the back and popping primers once in a while...
is this because the brass might be worn or a previous over pressure, if its a over pressure is there any other signs I can look for to know for sure...
any help would be appreciated
thank you

 

[17874]

In my humble opinion, I would say you are way over pressure. What do the primers look like on fired cases? 18.4 is listed as max on 135 grain projectiles, so with a 147 you are over pressure.

 

[zuke]

Those are ALL going to be case head seperation's.

 

[insight3b]

The brass has met its end and deserves the scrap pile. I usually crush brass with a pair of pliers before it goes in the scrap bucket to remove any temptation of trying it just once more

 

[demolitionman]

Holy impending case head separation!

 

[gvanhyning]

Could be from full length resizing and bumping the shoulders too much.

 

[Laseredge]

All of the above, and the powder may be too slow for your barrel/gas system/buffer combo. (I don't know the round at all)
The chamber pressure is too high as the bolt unlocks and extraction begins.

I had case bulging in a 24" 6.5 Grendel w/ rifle length gas system using 8208XBR.
Too slow a powder with too much dwell time in the system.

 

[afate45]

It's hard to tell due to the angle, but are those all the same bullet? I assume so because you said they are m80s. It looks like your seating depth is varying wildly. Full cannelure visible on the 2nd one down, others barely, some not at all. This could be a cause for pressure issues?

 

[High Binder]

Your seating depth is a mess but it looks like your brass is done. You might need to swap to a small base die when you get new brass but it looks like too much FL sizing to me. You might consider neck sizing until you have to bump the shoulders, that would extend your brass life a lot.

 

[doc76251]

You reloaded that brass? Really!?!

Ummmmm other than over pressure you also have a chamber issue. That brass is not supported fully. Almost like your barrel needs another full turn or so into the collar. Might want to have that looked at before you squeeze another round. Catastrophic failures can hurt, a lot.

Cheers,

Doc

 

[gvanhyning]

You reloaded that brass? Really!?!

Ummmmm other than over pressure you also have a chamber issue. That brass is not supported fully. Almost like your barrel needs another full turn or so into the collar. Might want to have that looked at before you squeeze another round. Catastrophic failures can hurt, a lot.

Cheers,

Doc

This is being fired in an AR platform and screwing the barrel is not an option. It's been my experience with AR's that FL resizing is required which led me to believe it was too much shoulder bump. I have experience this issue with bolt guns too and it was do to too much shoulder bump in the FL die.

 

[joseph-98]

it is to much shoulder bump... I just tried to load 3 more and they created that line..

 

[MikeeBooshay]

Seating depth may be OK, but the case length is likely the real reason for the different looking depth. Case length changes a lot with incipient case head seperations.

YOu can have any of a several reasons for this - too much shoulder bump, too much headspace, are two of the usual culprits.

 

[Iamironman]

To me it looks like the sizing die is not right, and it's over sizing the brass. What brand of dies do you have?

 

[joseph-98]

rcbs dies man this is a tricky one lol..... I have 223 brass cut down to 300 black out and I have a lot of 300 blackout.... i made sure all of them are the exact same length and only the 300 blackout stamped ones are f'in up..... i don't get it... i have cleaned the dies and made sure all the stuff was right.... but wont work right on the 300 blackout stamped once lol..
...

 

[thespecialist]

Holy smokes! 18gr of H110 under 147's? Brother, you're so far over max pressures it's a miracle the brass lasted that many loadings. Cut down 223's have slightly more case capacity than the Rem/AAC Blackout brass and are over pressure well before 18gr. It's a wonder you're not smoking the primer pockets after the first firing.

 

[Frostbite]

The problem is that load is way over pressure. The brass is starting to flow out of the end of the chamber upon firing. If the edge were caused by the resizing die, it would be a smooth radius instead of a sharp edge. Remedy, reduce load by at least two full grains.

 

[Sniper Uncle]

What jumps out at me in your photo, is the "apparent" disparity in case size...the shoulders seem to be in some cases crooked, and in some cases at different lengths from the case head. Is that me, or is it a bad photo???
Anyway, Hodgdon does list 18.4gr as max load for a 135gr Sierra HPBT. Not saying it isn't a hot load, not saying it isn't overpressure, but 2grains high???
Could this be a combo of too much headspace and worn out brass?

I ask these questions out of a desire to learn, not to question the experience of those who have all ready posted here.

 

[rgky1]

I'd highly recommend backing down your charge of H110 with the M80 147FMJ's to around 16.5 grains. It'll cycle your rifle and has decent velocity. 16.5 isn't quite maximum but it's easy on brass. You using a small based sizing die?

 

[Unknown]

Yep, over pressure. Either that or you have the first 300 Blackout magnum cases that headspace the same way as the 300 Win mag...(NOT!).

 

[Sniper Uncle]

Sooooo, why do the cases look malformed? Is that an optical illusion?
Still trying to learn.

 

[Ledzep]

My guess here is that the over-pressure loads are expanding the web and body of the case (how they still hold primers 4-5 loads in is beyond me), and the resizing die doesn't go all the way down the case.

So what you get is a belt formed from expanding around the unsupported (by the chamber) area of the brass, that doesn't get 'squished' back to shape by the resizing die.

Popping primers is a sure-fire way to know to back the hell off in a hurry, by the way, OP.

edit to add: The seeming seating depth variance could very well be caused by stretching brass from over pressure, then resizing if the OP isn't trimming them all to the same OAL. Or it could be mass-produced bullets from different factories, years of production, countries etc...

 

[Sniper Uncle]

I'm looking at the shoulder. The shoulders seem to be "crooked"

 

[ksthomas]

You've definitely got something screwy going on here, but I'm not at all sure it's a pressure problem per se. And those aren't incipient head separations, I'm fairly certain of that. To begin with, they're never this uniform, and you don't see them going all the way around the case until they actually separate. You've got something going on with the dies, and how they're set, and possibly something with the rifle itself. Maybe something with the barrel extension itself?

Couple questions here; how much of a difference is there the at the "belt", and just ahead of it in terms of actual diameter? Are you seeing any other pressure signs, such as ejector marks or loose primer pockets? Have you actually has any separations, or cases that started to split? Lastly, are you using a bump gage or other case gage to set your dies up when you reload for this one?