Markings on Fired New brass

[RonS]

Guys, my friend has an AR-15 with an 8 twist, the chamber dimensions are unknown to me and its owner. I reload, he doesn't so he gives me all his brass. Today I was resizing his brass when I noticed markings at about .030" from the very end of the case mouth that look like they could have been made by the lands and grooves. I inspected some of the unfired rounds from the same lot of factory ammo he has and these marks are not on the new brass, although it is very slightly crimped. The loaded unfired brass measures 1.753" and I am trimming it to 1.750" after the first firing. I have fired this same new ammo in my AR and my bolt gun with no markings. Both my guns have a wylde chamber. I did notice his AR produces more felt recoil then mine, his is a 24" varmint A3 whereas mine is a 20" A2 service rifle. Is it possible that his rifle was not chambered properly? Does this make his gun unsafe?

 

[Shynloco]

Let me say from the outset, I'm no AR lover having shot AR's in my younger life 'til the cows came home. That's probably why I gave my tricked out AR to my son who loves playing Rambo with it, even though he's 33 years old. Anyway, AR's are notorious, especially those from the 80's, of being "hard" on brass. That's is why though I still reload for that AR, there ain't no way in heck I'm going to expose my bolt gun .223 to those scared up and extractor beaten AR casings. Also keep in mind, depending on your load in the AR, it's a shorter rifle and therefore the kick might well be more, not to mention a gas gun cycling could easily create the false feeling that theres a "kick" just because of the movement off aim point. BTW, I still have a habit of picking up reasonably good AR casing at the range, just so I can reload those for the AR and not to have to buy brass for that thing because of the damage it does to the casings and giving much shorter case life than the bolt gun does. This would be a guess, but I'd be willing to bet I can get 50+ reloads out of my Lapua brass in bolt gun and probably those same brand cases would be history at 10 reloads in that AR. Even the newer AR's with much better quality barrels still beat the snot out of good brass. Just my observations and bias toward bolt guns.

 

[jhord]

The case necks are probably being scratched by the feed ramps. One of my AR's does that, but I've been too lazy so far to go in there and knock off the sharp edges.

 

[itchyTF]

I'd suggest measuring the chamber with something like this - http://www.sinclairintl.com/.aspx/pid=32925/Product/Sinclair-Chamber-Length-Gage to determine if that's the issue.

 

[284driver]

Two small markings that look like a snake bite on the necks, correct? If so that's from the case neck hitting the locking lugs upon extraction due to the plunger pushing the case towards the ejection port when it is unsupported after clearing the chamber. Two of mine do it. One does not. Your gun and buddy's are good to go.

 

[RonS]

Shynloco........

jhord, thanks i will tell him to have his gunsmith look into that

itchyTF, I use a Hornady case length gauge (Stoney Point) when I load for my rifles.

skyav8r, I am familiar with the two marks you are referring to but these markings are not like a snake bit, they go all the way around at the mouth of the neck and mimic the 6 lands and grooves of the barrel.

 

[284driver]

I misunderstood. A chamber casting might be in order.

 

[itchyTF]

shootr -

The tool I referenced is used to measure the length of the chamber not to determine bullet seating depth to lands.

If you think your cases might be engaging the rifling, the Sinclair tool will determine if your cases are too long for your particular chamber.

 

[RonS]

Dave , what you're saying makes good sense. itchyTF, I will have to invest in that Sinclair tool for my guns as well. The cases are 1.753" long before there first firing (new factory ammo, 75gr BTHP), his upper is an off brand the he bought online some time ago. With a scope on his rifle it shoots a +/- 2" group at 100 yards from the bench. I shot the same new ammo in my AR and boltgun from the bench and my groups were under 3/4 MOA.

By the way, I know this is not Lapua brass but the consistency in the weight is better than some of the major brands. I reload this stuff for my AR's that I use for high power and plinking. I have gotten 10+ reloads out of this brass in the past with no signs of stress in the cases or primer pockets. Very rarely do I have to trim this brass a second time. Case capacity is less than Lapua but I get better results with this brass without using a full case of powder and adjusting the seating depth. Works for me from 100 - 600 yards on paper, steel or groundhogs.

 

[markm87]

What you're describing sounds like the Factory Crimp indentions. Is this Remmington AMMO by chance?

Some UMC ammo will have these markings, and some won't. See if Rayjay has any unfired pieces of this ammo you could look at.

 

[DougMH]

Yes, I'd say try using all plastic mags and see if you're still seeing this.

I supposed it could also be from a gritty chamber. A full-length resized handload chambers ok, expands when fired and is then dragged through the grit during extraction.