FMD The Centaur's Spareribs™ Joined Aug 2004 Posts 11233 EE 100% (43) WI, USA

Posted: 10/17/2012 2:34:30 PM EDT [Last Edit: FMD] [#1] Originally Posted By Murrays: We're not *all* snobs...   We used the "gage" and checked a S&W M&P15 yesterday that was marked 5.56 and it truly was. Then I checked a SP-1 that was marked on the barrel, "0 MP 5.56 NATO 1/7" and it was Not 5.56 but actually the smaller/shorter .223. Guess we'll find out what other brands are in time. It may vary lot-to-lot with some manufacturers.  Also, short chambers aren't the only cause of overpressure signs with in-spec ammo... excessive headspace will also cause problems that can appear to be overpressure (popped and pierced primers, stretched cases, and case head separation).  Edit:  The problem doesn't get any better when reloads/remanufactured ammo (otherwise in-spec, but using once-fired brass) are run through the gun.

"I want to be just like you when I grow up" - glenn_r

SGL_Shooter Living life in the low ready. Joined Dec 2011 Posts 3574 EE 100% (273) USA	Posted: 5/13/2014 2:20:41 PM EDT [#2] I had three blown primers yesterday in my Bushmaster XM15 using Federal XM193 in the brown box. I think it is the ammo, I've never blown a primer, and I've put 3600 rounds through this rifle.  Wolf, Tula, PMC, Remington, Federal M855, etc. My friend shot 80 rounds of the same ammo through the same rifle, not a single blown primer.
	Originally posted by broken_reticle: "Second thing I learned on ARFCOM was to never google anything suggested. Ever. Because the first thing I learned on ARFCOM was what a blue waffle was."

Smithrob9999 Joined Sep 2013 Posts 135 EE 100% (21) TX, USA

Posted: 10/21/2014 9:01:25 PM EDT [#3] Hello all, I have some huge issues with a CMMG M4. It won't go more than 2-3 rounds without popping a primer. 1. The gun is perfectly cleaned and oiled. 2. The ammo is top quality, no reloads. It's doing it with Federal XM193, IMI, S&B, Wolf Gold, etc. 3. The cases don't appear to be stretched.. It's gotta be a chamber issue, I can't think of anything else. I've never seen a gun pop primers on 6 different ammo types. I posted a question on CMMG's industry page here and got no response so I sent an email to them and just sent the gun off. Any idea what they would do to fix it and how long this takes generally ? It's my only AR so I'm thinking I should have went with a Colt, BCM, or PSA and in fact I may still get a PSA midlength.

RyanO20 Joined Sep 2014 Posts 177 EE 100% (49) KY, USA	Posted: 3/18/2015 3:32:58 PM EDT [#4] What if this happened with both 5.56 and 223 rounds? The primer blowing out that is.

Humpy70 Joined Sep 2005 Posts 193 EE 0% (0) SC, USA

Posted: 7/8/2015 7:58:40 AM EDT [Last Edit: Humpy70] [#5] Just a idea for you.  Have you run your cases through a MO GAGE to determine how much forward shoulder movement you are getting?   Have you borescoped your barrel?  I have seen copper jacket deposits in bore that would definitely drive pressures out roof. Are you getting primer punctures? To be on the safe side have you defouled barrel with a copper solution? Sweets or Humpy's White?

rustymusket Joined Jul 2007 Posts 46 EE 0% (0) MI, USA

Posted: 12/10/2015 11:43:20 PM EDT [#6] There was a similar situation at our range, and while blown primers are supposed to take the rifle out of action by fragments lodged in the FCG, this guy just pulled the take-down pin after unloading the rifle, inverted it, and "shook the blown primers fragments out on the ground", closed the rifle, reloaded it, and continued shooting! I later asked him how he did this amazing thing, and he showed me what he called a "rubber lower receiver rug" that fit on the floor of the lower receiver under the FCG.  He said they were available from DPMS. I called the company and no one heard of this item.   Ditto for a Google search. Has anyone heard of these AR "lower receiver rugs", where can I get some, and has anyone ever used them? rustymusket

Rolls-Royce Joined Mar 2011 Posts 11 EE 0% (0) CA, USA	Posted: 3/15/2016 1:15:22 PM EDT [#7] Looks like it's been discontinued.

Originally Posted By wrecktech:Okay here goes the latest details:Headspace Check:Forster .223 Go Gauge 1.4636 - Closes with no problemForster .223 No-Go Gauge 1.4666 - Closes with no problemForster .223 Field Gauge 1.4696 - Resisted closing but then popped closed and opened without any problem with charging handle.?????? .223 (Max-Field) 1.4736 - Would not closeIIRC, All the gauges were purchased from Brownell's This rifle has excessive headspace.  The cartridge is driven forward by the firing pin and the case  expands to hold it in place, the primer is pushed back to the bolt face, then the case head is pushed back to the bolt face, stretching the case.  If you reload, you will only get a few reloads before the case head separates.  The period where the primer is pushed out of the case head can lead to piercing.  A common cause of cratering and/or blanking is too much clearance between the firing pin and the bolt, resulting in not enough support for the primer.Plus one

It closed on a field gage! The barrel and bolt in combination don't work safely based on that information alone.

The ammo is way too hot in that rifle and if he has fired a lot of it that is probably why he has a premature headspace problem.

Did he ever run steel cased ammo and through that rifle? It's known to build a carbon ring in the rifle's throat that would spike pressure if it's not scrubbed out. The ammo behaves normazlly in the other rifle which tells me his barrel is the problem. If he thoroughly cleans the chamber and bore he might get headspace back into a safe range by replacing the bolt.

If that doesn't work he needs a new barrel.

borderpatrol Member Joined Sep 2008 Posts 9067 EE 100% (5) MI, USA	Posted: 3/20/2018 12:08:55 AM EDT [#8] Quote History Originally Posted By ronemus: