Advice about pressure signs

[myrifle]

Good suggestion. I forgot to mention that I pulled the ejector and rounded the edges. I checked it up in a drill press and ran a fine diamond file over the edges. It didn't help which really pissed me off because I was sure that was it. I then pulled out the spring and clipped a couple coils. After that I still had the marks but ejection was really weak. Most of the brass landed on the shooting bench with one stovepipe which had never happened before.

After that I tried a different bolt in the same carrier. When that didn't help I threw in the BCG from my 16" BA upper that has no issues and again, no change.

I have to admit, I did a lot of checking things and rechecking things since my last post because I really feel like I should be able to figure this out and I honestly hate asking for help.

I may try loading them another 0.020" shorter and trying again. I've never measured neck tension so I guess it's possible that I don't have the jump I think I do after the bolt cycles.

What brass and what full length sizeing die are you useing?

[fdbyrne78]

What brass and what full length sizeing die are you useing?

Good question. It has all been Hornady brass and Redding dies.

[fdbyrne78]

Here's a pic of one of the pieces of brass. I'd already knocked the primer out so you can't tell anything from that. I wouldn't consider them flat or cratered. They still had rounded edges. The black line is a sharpie mark where I was keeping batches of brass separate.

[Klem]

78,

Can your ejector depress so it is at least flush with, or even slightly more than the bolt face?

[fdbyrne78]

78,

Can your ejector depress so it is at least flush with, or even slightly more than the bolt face?

Yes, it does. It takes a firm push, but it does depress at least to flush with the bolt face.

[VASCAR2]

A lot of my factory Hornady ammo brass has ejector swipes after being fired in a couple of my AR-15’s. If the primers look ok I don’t worry about it. I have a 16” carbine gas length upper that was over gassed and it was the worst for having ejector swipe on the brass. I started using a RCA adjustable gas carrier key and reducing the gas has helped to reduce the marks on my brass.

I’ve noticed ejector swipes over the years on 5.56/223 ammo and never got concerned under most circumstances. Once some of our Department Lake City 55 grain M-193 5.56 popped a couple of primers. It was hot one day which might have been a contributing factor. One blown primer locked up one of the Armalite 16” carbines during a qualification. As far as I could tell the popped primers happened on different days in different firearms.

[biodsl]

First, how fast can you push a 123gr bullet out of your 20" barrel before harming your brass? I'm trying to see if I have unrealistic expectations for my barrel and this input would go a long way to helping me understand that.

I had a 20" Lilja (which is actually 19.5" of barrel and chamber). My 123 Amax load of 31.2gr of CFE223 was around 2450fps standard pressure and temp. Only the slightest hint of ejector marks on some brass.

[Klem]

Yes, it does. It takes a firm push, but it does depress at least to flush with the bolt face.

Well, that blows my theory that maybe when it goes off it's left with an imprint because the spring won't let the ejector compress past the bolt face.

I'm with Vascar on this - it's probably nothing too concerning. If the primer is not flattened, it cycles, and the rest of the case looks OK then you could keep shooting until you know more.

[fdbyrne78]

Thanks everyone. I'm pretty certain that the loads I have worked up are safe in that I'm not in any danger of blowing my face off. I'm just cheap and would like to use the same brass for more than a couple of firings.

In all honesty, I'm starting to doubt my jump measurements. I may be a touch too long and want to rule that out. I'll report back.

[LR1955]

A lot of my factory Hornady ammo brass has ejector swipes after being fired in a couple of my AR-15’s. If the primers look ok I don’t worry about it. I have a 16” carbine gas length upper that was over gassed and it was the worst for having ejector swipe on the brass. I started using a RCA adjustable gas carrier key and reducing the gas has helped to reduce the marks on my brass.

I’ve noticed ejector swipes over the years on 5.56/223 ammo and never got concerned under most circumstances. Once some of our Department Lake City 55 grain M-193 5.56 popped a couple of primers. It was hot one day which might have been a contributing factor. One blown primer locked up one of the Armalite 16” carbines during a qualification. As far as I could tell the popped primers happened on different days in different firearms.

VC:

Thats really strange about the M-193. Never experienced any of it blowing primers and I can not estimate the tens of thousands of rounds of that stuff I have either shot myself or seen shot when we had the A-1's and even well into the A-2 era.. Primer no doubt either got caught in the trigger or fell into the breach. Major PITA to remove.

About the ejector mark on FD78's brass. That is a pretty deep mark on the brass. I don't think I would let it go.

Cut off one coil from the spring and see? What do you think?

LR-55

[montana]

VC:

Thats really strange about the M-193. Never experienced any of it blowing primers and I can not estimate the tens of thousands of rounds of that stuff I have either shot myself or seen shot when we had the A-1's and even well into the A-2 era.. Primer no doubt either got caught in the trigger or fell into the breach. Major PITA to remove.

About the ejector mark on FD78's brass. That is a pretty deep mark on the brass. I don't think I would let it go.

Cut off one coil from the spring and see? What do you think?

LR-55

The 5.56 barrels I experienced popped primers had short chambers and not true 5.56 throats..I have never seen any Colt barrels that had chambers out of spec..

[LRRPF52]

I went back to the range with a variety of charge weights from a variety of different powders. I used AR Comp, Benchmark, Varget, BLC(2), and CFE223. Still ran into ejector swipe earlier than I figured. I still need to go lower to find charges with no swipes.

While processing some brass I realized something that I'd like to get some opinions on. The fired cases are coming out with a 1.223" length to shoulder using the proper comparator. I'd sized the cases to 1.213" previously because my other Grendels produce fired brass that measures 1.217" or 1.218". It seems that the chamber/bolt combination for this rifle allows for significantly longer cases than my other Grendels. I swapped the BCG's between the Grendels and the results were kind of interesting... at least to me. With this rifle, I can bump the shoulder back to 1.218" and they chamber just fine. If I try to chamber that same round in my other Grendel it won't return to battery. My 1.213" cases do allow the BCG to return to battery in that other Grendel. Both bolts have bolt head depth measurements .137" so the variance is somewhere else.

I really don't mind keeping my brass separate for different guns. I also don't want to have to if I don't need to. Would an apparent headspace of .010" have any impact on the marks that I'm seeing? Obvoiusly case life may suffer from oversizing the cases and I get that part.

A longer chamber can allow the rapid case growth to slam the brass into the bolt face with more velocity as the brass instantly expands under pressure.

There was a discussion recently about this relative to lower than published start loads, where the peak pressure wasn’t building as fast, and therefore didn’t provide enough brass obturation to the case walls, and therefore increased rearward case thrust. This isn’t the case with your loads, but just a point about what can contribute to ejector channel extrusion.

Do you have a highly-polished chamber in the rifle that is showing those signs by chance?

A high polish chamber can exacerbate this problem, preventing brass-to-chamber wall adhesion, which increases bolt thrust.

Also, a chamber on the larger diameter side requires the brass to expand outwards more to purchase the chamber walls, and could lead to more bolt thrust especially when combined with a high polish chamber.

AR Comp is a little on the fast side under 120gr and up, so we have to be careful with it similar to how we treat 8208XBR.