Cases bulging in 223 AR15?

[BCP]

A friend of mine bought a S&W AR and the fired cases bulge slightly, not much but enough to see it when you place them on a flat surface. The case head mics at .374 but then grow to .378, I thought maybe excessive headspace but I didn't see any growth in length so now I'm thinking maybe the chamber is every so slightly too large? The barrel is marked 5.56MM, it shoots well and is accurate I'm just concerned this will case premature brass wear for him since he wants to reload for it.

 

[McCrazy]

Is he shooting handloads or factory ammo at this point? If the cases are bulging it will drastically shorten their reloading life. I would guess an out of spec chamber but is hard to tell at this point.

 

[BCP]

Factory and handloads. I'm thinking his chamber is a bit too large in the body area.

 

[McCrazy]

Yeah, if firing factory ammo then the chamber is probably out of spec.

 

[gixxer822]

Cerrasafe the chamber, then look at the gas system. If the chambers fine then I'd say it's overgassed.

 

[BCP]

Cerrasafe the chamber, then look at the gas system. If the chambers fine then I'd say it's overgassed.

I'm positive it's not overgassed in fact it doesn't run on lighter loads only 5.56 pressure rounds run it 100%. I have some of the brass with me now I will post some pics with calipers showing the lengths, it's almost like the chamber is short and fat.

case head=

about 1/8" up the body from the case head=

Overall length is 1.744, resizes right back to 1750 (what I trim them to) also the shoulder, neck, all those measurements are the same just the body of the fired case are 1-2 thousandths too big

 

[BCP]

You can put your finger on a full length sized case when it's in the chamber and it moves around noticeably same for factory new cases also headspace length is very tight, near minimum for a GO. It's like it has a tight shoulder and neck but oversized body? WTF

 

[LRRPF52]

Is it a carbine-length gas system with 16" barrel? If so, add buffer weight and see what happens.

 

[BCP]

Is it a carbine-length gas system with 16" barrel? If so, add buffer weight and see what happens.

It had a 4oz buffer didn't cycle with it. 2.9oz it cycles ejects fine. I don't think more weight is the answer.

I have been looking at this barrel for about an hour now and am pretty confident that the chamber is out of spec, specifically the area towards the rear.

 

[McCrazy]

Sounds like you need to be contacting S&W customer service. Sooner the better.

 

[ORD]

S&W's QC is SERIOUSLY lacking at times (remember the UNRIFLED, SMOOTHBORE barrel a while back on an M&P AR...good times!).

I would advise your friend to get in touch with them ASAP and get them to inspect and replace the barrel which appears to have not been properly chambered. I'd provide them with all the data you've provided here, along with your observations of the problem. My "guess" is that they'll come up with some BS answer that the barrel "checks out" and is otherwise "within specifications" despite evidence to the contrary, but that clearly isn't. Otherwise, shoot the @#$% out of it and replace it with a quality tube in a couple thousand more rounds that will be even more accurate and won't tear up/reduce the service life of your friend's brass.

 

[bustin]

A friend of mine bought a S&W AR and the fired cases bulge slightly, not much but enough to see it when you place them on a flat surface. The case head mics at .374 but then grow to .378, I thought maybe excessive headspace but I didn't see any growth in length so now I'm thinking maybe the chamber is every so slightly too large? The barrel is marked 5.56MM, it shoots well and is accurate I'm just concerned this will case premature brass wear for him since he wants to reload for it.

The case will always expand to the chamber wall, .004 is just about right. Pull up the specs on a 5.56 chamber and see what the dia should be before calling S&W.
The cases must be sized smaller than the chamber so they slide in a semi auto. Looks in spec to me.

 

[FCS]

Factory and handloads. I'm thinking his chamber is a bit too large in the body area.

What powder and bullet?

Don't look at a reamer print for a Wylde if you think 0.378" is large at 0.200" above case head.

 

[BCP]

The measured cases jive pretty closely with the 556 Wylde specs in that PDF sheet. .2560 for case neck @ shoulder, .3560 for shoulder, .378 for case head. I guess I've just been spoiled by tighter chambers.

 

[Jethro80]

sounds like a sloppy chamber

 

[bustin]

The measured cases jive pretty closely with the 556 Wylde specs in that PDF sheet. .2560 for case neck @ shoulder, .3560 for shoulder, .378 for case head. I guess I've just been spoiled by tighter chambers.

Do you mean .223 chambers like in a bolt rifle? 5.56 Nato chambers are bigger than the Wylde chamber. .223 chambers limit the ammo to 223 loads, 5.56 mil spec loads at 58,000 psi like M193 and 855 should not be used in a .223 chamber. It's not a good idea to use .223 chambers in a semi auto rifle.
Measure a new case dia. fire it and measure the fired diameter. Now resize it and measure the resized diameter. New should be around .373, fired .378-.380 and resized .375. or .002 smaller than a fired case. Regular size dies are made to resize brass .002 smaller than the smallest smallest chamber size, not the brass size. Small based dies are made to resize .004 under the smallest chamber size. If you look at the PDF above you will see the smallest "match" chamber dia is .3779" That is only 1/10000 -1 ten thou smaller than what you say you measured. 1 ten thou is 1/40th as thick as a piece of common copy paper.