HUGE PROBLEM WITH BRASS IN MY RIFLE

[Jmanchen]

Hello everyone. New to the group and also new to the 300 BLK platform. I'm experiencing a huge issue with my setup. When there is a live round in the chamber the bcg is very difficult to open and clear the chamber, but the bigger problem is with my brass once it is fired. The neck is being stretched in one small area of the mouth and I have also experienced total neck failure with a horizontal crack. This is brand new Norma brass I'm using in these loads. I will post the setup of the gun and also my load data. Hopefully someone here has an idea of where to start on fixing this issue, I have been reloading for my bolt guns and my other AR in 5.56 for 5 years and have shot thousands of rounds out of all of them and I have never came across anything like this. Thanks in advance.

New Aero Precision Upper 10.5"
New Noveske BCG
New CMC Carbine Spring and Buffer

Load data-
17.5gr of Accurate 1680
185gr Berger Juggernaut OTM
New Norma Brass
Rem 7 1/2 BR primers
2.150 COL

[BobinNC]

There's two places I'd start to diagnose this problem:

One is your reload. Do you have a case gauge? If so which one.

Second, and most likely with the picture you provided, is your chamber. Can you do a chamber cast, or maybe know a gunsmith who can? Alternatively pull that barrel and send it back to Aero.

I would not fire that rifle again with your reloads, until both your reloaded rounds pass a case gauge, and your chamber has been cast or inspected as OK by the maker.

Can you beg or borrow a couple of factory rounds to test as well.....Plus what die set are you using for your reloads.

What do your primers look like? Also if you have a chance can you weigh a empty new piece of Norma brass, without a primer. I seem to remember that Norma 223/5.56mm brass was quite heavy, I just want to verify how heavy this Norma 300 BLK brass is as compared to say Hornady or RP brass.

My Starline brass I use is quite heavy and I reduce my loads compared to book to accommodate that. I just trying troubleshooting 101 to eliminate as many possibilities as I can think of.

Thanks

[20X11]

What is your trim length on the cases?

[dellet]

Hello everyone. New to the group and also new to the 300 BLK platform. I'm experiencing a huge issue with my setup. When there is a live round in the chamber the bcg is very difficult to open and clear the chamber, but the bigger problem is with my brass once it is fired. The neck is being stretched in one small area of the mouth and I have also experienced total neck failure with a horizontal crack. This is brand new Norma brass I'm using in these loads. I will post the setup of the gun and also my load data. Hopefully someone here has an idea of where to start on fixing this issue, I have been reloading for my bolt guns and my other AR in 5.56 for 5 years and have shot thousands of rounds out of all of them and I have never came across anything like this. Thanks in advance.

New Aero Precision Upper 10.5"
New Noveske BCG
New CMC Carbine Spring and Buffer

Load data-
17.5gr of Accurate 1680
185gr Berger Juggernaut OTM
New Norma Brass
Rem 7 1/2 BR primers
2.150 COL

Load is too hot, it's way over gassed and brass is possibly too long.

And I will add that there is possibly enough powder compression to deform case causing the sticky rounds if it's not do to neck length

[Jmanchen]

Hey guys, just got home and sat down at my reloading bench. Oddly enough, I had one round left from yesterday that has the 185gr Bergers loaded into it. I previously had loaded some 220gr sub sonic loads. For shits and grins I took the gun outside and chambered one of my subsonic rounds and had zero issue pulling the charging handle and clearing the chamber, so I went back inside to my bench and got out my micrometer. I found that I have a slight bulge (unable to really see with the naked eye, 0.005") right behind the shoulder compared to the loaded subsonic ammo. As far as trim length goes, these were all hovering around 1.362 +- a thousandth, max length being 1.368, I loaded them up just to run a mag through the gun before I develop a load for it. I've yet to shoot the sub loads because my can is still in ATF jail. Gonna run these sub loads when I get a chance just to see what we get for results as far as the necks go.

[dellet]

Hey guys, just got home and sat down at my reloading bench. Oddly enough, I had one round left from yesterday that has the 185gr Bergers loaded into it. I previously had loaded some 220gr sub sonic loads. For shits and grins I took the gun outside and chambered one of my subsonic rounds and had zero issue pulling the charging handle and clearing the chamber, so I went back inside to my bench and got out my micrometer. I found that I have a slight bulge (unable to really see with the naked eye, 0.005") right behind the shoulder compared to the loaded subsonic ammo. As far as trim length goes, these were all hovering around 1.362 +- a thousandth, max length being 1.368, I loaded them up just to run a mag through the gun before I develop a load for it. I've yet to shoot the sub loads because my can is still in ATF jail. Gonna run these sub loads when I get a chance just to see what we get for results as far as the necks go.

So the answer to the original question is complex.

The cases are basically out of spec. Generally new brass is minimum headspace. When you combine minimum headspace with maximum overall length, the necks can be long enough to crimp the bullet in the end of case portion of the chamber.

You packed so much powder into the case, with so much force, it caused the case to expand, the reason for sticking in the chamber. With no room for case expansion, this raised chamber pressure even more, compounding problem number one. All the brass had to expand forward.

Add to those two problems, you had a very hot load. 17.5 grains is a high mid range load for a 185 grain bullet, but you had about an extra .200" bullet in the case. That is a pretty large deviation in data.

If you look at the rim on the case second from the left, there are some pretty deep gouges from the extractor. I would not be surprised if the case head is also bent there. A hot load and an over gassed system that pulls a case out of the chamber before it has had a chance to start to shrink does that. It can pull a case apart.

Your sub load should be fine. Unless you are using a very fast powder. In general 1690 will not produce enough pressure as a sub to fully expand a case.

Not sure where you got the load data, but that source should probably be ignored.

[Jmanchen]

Thanks for the info. I’ve reloaded for my .223 up to my 338 Lapua and have never had an issue like this. I appreciate it. New to this 300 BLK platform. Never bulged a case before, and what threw me for a loop is that they loaded with no issue on my press. Usually you can feel it in the throw when you are “overloading” a case. That’s why I had no worries. Again, thank you. Scrapping that load, along with almost all the brass from the 60 round mag from yesterday. Damn shame. The necks have been stretched, not sure I even wanna mess with resizing them and trimming them back down. Some grew 0.020”. There’s a good chance those necks will fail on the next firing in my thoughts. Overworked.

[Jmanchen]

My subs are at 11.5gr of A1680 at 2.100” col

[20X11]

I have a couple of chambers that have issues over 1.362 trim length. I trim all my brass to 1.358 initially, and retrim if they get over 1.362.

[pj-schmidt]

I agree with the others that running max brass oal while likely sized to min spec seems likely to be problematic.

Although I have never loaded that bullet, I would expect your COL to be 2.20-2.25". Running so much shorter seems like an invitation for excessive pressure on you supers load.