My LC XM193 lot 52 is on the warm side in 3 Colt chrome lined barrels.  Some slight marks on the case head and the primers are pretty flat.  It is HOT in my WOA SS Wilson with Wylde chamber.  More pronounced markings on the case head and pancake primers.

I've quit shooting it in the Wilson barrel.  I keep forgetting to run it through the chronograph to see what's happening.

I think it's quite possible for this ammo to act ugly in a SAAMI chamber or short/tight throat.

Tweak: The Dimensions on the case necks from the casts are:

Gun / Near Case Shoulder / Near Case Mouth
S-04 / .2576 / .2560 (Sig 551 - 5.56 NATO)
A-08 / .2568 / .2558 (RRA - .223 Wylde)
A-04 / .2586 / .2572 (Armalite)
Spare #1 / .2585 / .2564 (")
Spare #2 / .2586 / .2560 (")

As far as contact with the ammo maker, funny you should ask! I just received a letter back from ATK / Federal just this week. They also report a similar problem with the San Antonio, Texas PD where they discovered their Armalite guns had .223 chambers so their cure was to return all the ammo. They also indicate that blown primers in commercial .223 is usually a combination of a weaker case (head & web), dirty-hot gun and high ambient temperature. Knowing that, their LE line of ammo uses a mil-quality case instead of a standard case and don't load to 5.56 levels. They also point out that "XM-193 is a machine gun compatible full mil-spec load." I would expect it to be hot! The Ammo-oracle states M-193 should give you about 3150 FPS out of a 16" barrel. That was what I got out of the 16" Styer-AUG from the get go and RRA guns were below that. I can't imagine there is any real specific difference between these two versions.

Since Armalite is apparently going to actually fix the guns and in the process cut the chrome in the barrel throat, what is the long-run effect of doing that? How much is that going to cut down my overall barrel life? Right now I'd have to say these guns probably have 7,500 to 10,000 round through them.

Originally Posted By Tweak: did you cast the entire chamber or just the neck and throat?

Nearly all of the chamber for most. I was trying very hard to avoid getting the casting caught behind the locking lugs. I was using a pouring tube I fashioned out of a toilet water supply pipe through the ejection port and closely monitored how much I poured into the chamber. Is there some more specific dimensions you want?

Originally Posted By Tweak: I'm wondering if the chamber diameter is undersized.

Here are the sizes I measured off the chamber casts:
S-04 (Sig 551) .3591 & .3768 (Nearest shoulder and end of cast respectively)
A-08 (RRA) .3572 & .3788
A-04 (Armalite) .3599 & .3787
Spare #1 (") .3591 & .3768
Spare #2 (") .3572 & .3752 (Short Case area cast)

-------------------------------------------------------

While I have your attention, I have a powder question. In the XM-193 a slower burning powder is used but the cartridge pressure is actually higher overall. Is the slower burning powder used so the pressure peak is not reached too fast and thereby reducing the potential for a KB?

When they develop a load are they looking to reach a certain muzzle velocity in a certain time or a certain pressure so the action will function?

Originally Posted By Tweak: the design concern was MV, IIRC gas port pressure wasn't quantified until the rifle had already entered service, that was part of the testing brought about by the troubles in RVN.

Do you know of someplace I can find this information?

do you see a pattern of behaviour related to the chamber dims?

Spare #2 was the original problem child with popping primers. A-04 has been one of the better behaved ones of the group. Spare #1 had its share of breakdowns to get moved off line but never blew a primer that I recall but did have very short distance from case mouth to rifling on the casts.

Originally Posted By Tweak: Originally Posted By wrecktech: Do you know of someplace I can find this information? The Black Rifle is the reference I'm thinking of, unfortunately my copy is currently in another county. Spare #2 was the original problem child with popping primers. A-04 has been one of the better behaved ones of the group. Spare #1 had its share of breakdowns to get moved off line but never blew a primer that I recall but did have very short distance from case mouth to rifling on the casts. So Spare #1 and A-04 are the better behaved ones (regarding pressure signs) and their chamber dims mimic (or exceed) those of the SIG control?

Your assessment is correct. It seems to me that perhaps, slightly tight chamber dimensions are less critical to the operation if the throat is correct. If the throat is wrong, the cartridge case is more "bottled up" by the tighter chamber and the pressure has no place else to go. Would that be correct?

I will be working up chamber casts on another rifle (A-09) that has also started blowing primers when I get back to work from my vacation. Heck for that matter I'll just do all the rest so I have the same information for each.

I believe that I have at least four different Lot #'s of XM-193 on hand. I had best run all of them through the chronopraph too. I figure I'll use one RRA and since it is acting up #A-09 for comparison.

No rest for the wicked....

For what it's worth here are some chamber reamer blueprints that were forwarded to me during this that I cleaned up and posted in the photo gallery.

-------------------------------------

223 Remington:


-------------------------------------

223 Wylde:


-------------------------------------

556 NATO:


-------------------------------------

Hope this helps those interested in this discussion. I'm still trying to figure out which dimensions correspond to some of the things I'm looking at. I've also looked at the dimensions from the Clymer site but they don't list a 556 NATO reamer. I don't know if anyone else does or publishes the NATO sizes.

ETA Picture link to new server restored.

Originally Posted By Tweak: those look familiar. funny how things get around online. not sure what you're asking?

I got them from a link to jobrelatedstuff.com which appears to be a mirror of the ARF Board. In the archives it is message #236946 talking about the Wylde chamber.

I'm not sure what I was asking either now that I look back. If you've got the stuff off the Clymer site for the .223 Rem. They list "A" thru "R" with a few missing letters and corresponding dimensions. Now being somewhat awake, and comparing to the same caliber from JGS I see that Clymer's "C" = JGS' "A" and a few others correspond directly and equally or within a couple ten-thousandths. One that I can't seem to find is CLymer's "L" Base to Shoulder at 1.234". On the JGS print it appears to be the "Q" dimension: 1.438". The other odd one is the Clymer Neck Length "L" of .2200" which appears to be the second dimension (0.19481) in the vertical series to the left of the stacked series starting with "Shank Length".

I guess what I need to do is make a spreadsheet with the dimension points on it and then measure all the same points on the casts for comparison. I think I've got most of them here in this series of posts but they are spread out over three pages. Bringing them all together would probably be more beneficial.

You mentioned the "Black Rifle" reference. Do you mean: Black Rifle: M16 Retrospective by R. Blake Stevens?

I also found some other books listed on Amazon if you could comment on relative value:
The M16/AR15 Rifle (A Shooter's and Collector's Guide) by Joe Poyer
New Black Rifle II: The M16 into the 21st Century by Christopher Bartocci
The M16 by Jean Huon
AR-15/M16: A Practical Guide by Duncan Long
Complete AR-15/M16 Sourcebook: What every shooter needs to know by Duncan Long
I already have The AR-15 Complete Owner's Guide by Walt Kuleck & Scott Duff that was interesting but not earth-shaking, however they mention: Black Magic: The Ultra Accurate AR-15 by John Feamster. Is that the book you referred to?

You will find variations in dimensions for the "same" chamber among the various reamer manufacturers.  Then ya have variations in the reamer manufacturing process.  Then you have the reamer cutting a smaller chamber every time it is used due to wear.  Then you have (sometimes large) variations in the actual chamber due to reamer wobble caused by poor equipment and/or lack of skill of the operator.

Bottom line is that 2 chambers with the same name probably won't be identical on all the dimensions.  This can drive you cracy if you are looking for a chamber to match the print.

None of this is to say that you can't get some prints and chamber casts and figure out what is going on.  You are doing a very good job of it.  Just don't expect any chamber to match any other or the print that you are referring to in every dimension.

Right now I am using the chamber casts to try to determine the throat angle (If I can. Maybe the better question is: Do I need to?).

Among the dimensions Billski & I am trying to pick up are the land (Bore) & groove diameter, the throat diameter (freebore), throat length and throat taper length. However I must admit that once again I am confused. Am I correct that the throat cylinder diameter would be the dimension just off the end of the case neck? I think I am correct in that this size should NOT necessarily be the same as the groove diameter?

The bore diameter is the original dimension of the hole drilled the length of the barrel and the grooves are cut during the rifling process. The throat cylinder may be cut in during the chambering process. Right?

In order to determine the throat length, I will have to carefully check the smaller bore dimension for changes between where they start on the cast and where they finally "bottom" out.

On another point, my former Rangemaster knowing about these trouble rifles called last night and left a message that there is an article in the September issue of "Guns" magazine relating to this issue. Has anyone else seen it? My copy hasn't arrived yet and now I'm getting impatient waiting.

wrecktech,
here's what I just posted on the Competitions forum;

I just read through the parallel thread on the "Troubleshooting" forum.  I'll throw out a couple of random thoughts and experiences for you.

1)  The velocities recorded for the Armalite barrels and XM193 are WAAAAY high for a 16" barrel.  That alone is indicative of excessive pressure for me (remember there's no free lunch).   Swollen/blown primer pockets are just extra nails in the coffin.  Normal velocities and pressure signs in the AUG?  Sounds like an Armalite barrel problem.

2)  I've played with the 223/AR and slow powders in a pressure measuring upper (strain gage).  Most of my experiences are with heavy bullets 69, 75, 77, 80 and 90's.  But I do shoot LC M855 (62gr) as a reference round before each session.  No pressure problems there.  ...and I did a workup with 52's and N540 which in the context of the situation and theories being floated is pretty slow.  I got up to 3300+fps with a 20" 6.5 twist Pac-Nor Wylde Chamber.  Surprising pressures did not appear to be excessive (strain and case/primer appearance).  Typically what happens when you're too slow on the powder burn rate is you run out of room in the case before you get to max pressure.
   


3)  Powder too slow being blamed for primer blowing because port pressure too high/carrier moving back too early/too fast?  (...or 16" barrel with a port closer in for higher port pressures).  I've seen the Carrier Weight System (to slow down carrier velocity)  help with case and even primer appearances but the benefit wasn't nearly as drastic as comparing a normal case to your blown primers.

4)  The last time I had to go through a similar academic exercise, it involved Federal Ammo (CMP 77gr Loading) and a theory about tight bores (Krieger).  In the end, that was inconclusive.  Ammo showed fine in my Pac-Nor barrels.  Fine in my Kriegers as well.  I ended up  suspecting chamber/throat, but never followed that to a conclusion.  (oops, that pic is of Fed XM223A which is an 80gr loading.  Similar pressure situation, similar conclusion though).


5)  If you'd like, I can run some of your ammo through my pressure Upper.  I suspect it won't show much through since the AUG's were fine.  E-mail me via my profile on this site if you'd like to send some over.  There are some practical challenges to work through, but I'm willing if you're interested.

6)  I saw the chamber drawings from JGS and some unanswered questions about dimension ie leade angle.  Here's a comparison of chambers from the Clymer prints if it helps;

Early on in this search I found I had three different Lots of XM-193 in my inventory so I limited my testing to just one. I finally took the time to test each lot out of one of the Armalites (#A-09) that most recently blew another couple primers and one Rock River (A-08).

Here are the results:

Armalite:
Lot# Lo Hi Avg Spread StdDev
Lot#8 3203.22 3260.16 3243.28 56.94 15.93
Lot#35 3232.30 3279.59 3254.34 47.29 14.14
Lot#39 3253.15 3313.70 3282.06 60.55 16.82

RRA:
Lot# Lo Hi Avg Spread StdDev
Lot#8 3015.69 3105.43 3056.71 89.74 26.62
Lot#35 3026.24 3139.25 3068.80 113.01 39.30
Lot#39 3036.87 3139.25 3076.16 102.38 33.31

I may just try to repeat in a different order to see if the gun heating up from the previous group has an effect on the numbers.

Tag for a problem I seem to be having again using the new wolf m193: Found this thread while searching for this old one about my previous issue!
archive.ar15.com/forums/topic.html?b=3&f=66&t=243133

Originally Posted By _RAGNAR_: This probably deserves a new thread but since I just read some of the most proffesional and scientific advice and reasoning every seen on the interent in this thread I thought I'd ask here. Has anyone done any scientific testing to determine the diferences in unlocking speeds based on weight of bolt carriers and buffers? All things being equal, would a M16 carrier be less likely to have suffered from this specific issue (blown primers) vs a cutt-away AR15 carrier? Thanks

I too wondered about what RAGNAR brought up. I have a pre ban HBAR COLT that shoots wonderful, but I always wondered why the primers looks so damn flat, like high pressure. Then I tried a Tubbs weight in the carrier and now the primers looks great with no pressure sign at all. I talked to Randall about this one time and he said something about the gas port on the Colts were all the large side to assure absolute functioning of the rifle and about the unlocking time and the carrier weight does help that.

Sounds like you fellows found the problems, but like RAGNAR and I said would be interesting to see what the offending rifles did with a carrier weight for curiosity.

JFA

I haven't posted anything on this topic in a very long time. The reason for this was I was directed by my agency administration to stop after a threat of legal action for libel. The end result was that all the uppers on the ten questionable rifles were replaced with brand new units from another maker. Since that time, there hasn't been a single ammo related failure. I also haven't had any more fractured extractors either.  The other uppers are sitting on a shelf in a closet gathering dust.

Bump to keep some good info active!

you said armalite was gonna take the rifle back and go over it??.

it was never a ammo problem,and doubt was chamber issue. if a ar is working correctly you can take a handfull of differant ammo,mix them up,,theyll all roll thru.

somtimes it a simple deal,,try a differant bolt,and all the stupid springs and doughnuts wont cure a extractor claw edge that not sharp and undercut correctly.  you can run a stock spring if the claw is correct.,,springs are a great help but are a bandaid to the real problem

a ar is very simple but you need the correct tuneup/balance.  every one i have will eat all ammo,and they never stop.,,ill bet your hs is ok,,try a simple bolt,,a colt one

i wouldnt do a thing if there gonna go over the rifle,,,,its almost always a simple problem,,and most times ar people will buy there way thru issues,,dont do that....


good luck  brad

Yes, they did take two back and when I got them back, the free-bore had been extended and velocity was reduced to normal levels. Since there was such a problem we replaced all the uppers with units from another vendor. Now the original units are sitting gathering dust.

where did the pics go i am having simuliar issues and yould like to see the markings on the casings

Luckily I was able to restore the pictures and put them on the new photo server here on ARFcom. The images have been restored to their original messages and should all be present. I'm sorry for any inconvenience the lack of pictures may have caused.

I am also happy to report that there have been some new developments in this saga. I hope to present new information in the near future with additional chamber cast photos, bullet / cartridge comparisons and chamber information. Without being too theatrical, please stay tuned...

Wow, glad I found this thread.  We have dozens of 10" M4s having this problem w/ XM193.  It is getting ridiculous having to take apart a gun every range day b/c a primer is stuck somewhere.

The uppers have about 4,000-5,000 rounds through them in 2 years.  When I first got mine my zero groups at 50yds had the holes touching.

Now, I could not get my to hold less than 4" at 25 yards of a benchrest...I had other shooters attempt to zero it w/ similar results...is this related to head space???

My rifle recently started having the same issues, I am loading 77 gr SMKs in LC brass with 23.0 gr RE15 at 2.26" OAL and blowing primers, today I had to beat my bolt with a punch and hammer to separate my upper from lower then beat the bolt assy out because a primer got caught in the bolt cam and froze the assy in the receiver.  Granted this upper has in excess of 8k rounds (most winchester 5.56 white box ammo and federal .223) but never an issue til the last 500 rounds or so, only with reloads that are over a grain lighter than max in all published reload data.  Today was the final straw, I will be replacing this CMMG upper with a LMT MRP and rebuilding this upper with a noveske barrel to go on a different lower I have laying around that doesnt see the range much.

didnt the first note say it had never had this problem,but just started?
Keep the reamer out of the chamber,try a new bolt ,or at least mike the thicknes of the locking lugs

a properly set up ar will run all ammo,i mix and match all the time when plinking,i never ever have faults/stops....     good luck     brad

My brass ejects from the rifle fine, unfortunately so do the primers from the brass.

Not to highjack this topic... but I have a question about reloading the brass.

The first 70-80 rounds out of my new AR exhibited the same overpressure marks on the case heads, just like the ones shown in the photos at the top of page 2 of this thread.

I'll need to test the gun a bit more, try some different brands of ammo, see if the problem continues, etc.

Absolutely no problems with ejection or feeding, though. However, all my new empty Lake City brass has these same marks on the case head. Is it safe to reload these, or should I kiss them goodbye?

I bought a headspace field guage to see if that was the issue and it did not close on it.

My rifle has also lost accuracy badly.  Going from 1" groups at 50yds to all over the paper consistetly.  I cleaned it.  I had several top shooters shoot it.  It is jacked.

Still blowing primers too.

Here is a test I did today:





XM193 on left.  Federal AE .223 on right.  Using my 10" CMMG 5.56 upper at 25 yards.  Didnt take forever, maybe 2-seconds per shot using my VFG on my range bag as a rest.  

The XM193 is what is also blowing primers.  There is something about this gun/ammo combo that is not working...

Were you having the primer blowing from the start or did it start later?

I'm sorry that I did not check back sooner to see your post. I firmly believe that the guns with problems were all .223 chambers. I recently used a neck & throat reamer made by Ned Christianson of Michi-Guns on six of the problem uppers and saw immediate MV drops to more normal levels. In recent correspondence with Tweak he said that he has seen more than one manufacturer mess up an order which are supposed to be NATO chambers and deliver .223 chambers and when the complaints start, blame the ammo rather than fix the problem.

Please remember that Headspace is measured from the base of the cartridge case to a spot on the shoulder. That dimension rarely changes and has nothing to do with the neck of the cartridge. The real question/problem area is the freebore and where the bullet engages the rifling in the throat.

First some questions... What kind of ammo? XM-193, Remington UMC or something in .223? Do you know what kind of barrel you are supposed to have? Do you have access to a chronograph? If so check the MV ASAP.

I was shooting Federal XM193 Lake City rounds with NATO headstamp. My DPMS is supposed to be a 5.56 chambered gun, and is marked "5.56" on the receiver and on the barrel.

The empties had pretty noticeable pressure marks on the bottoms: indents from the bolt face and stress marks from the extractor. They also had light vertical scratches along the case walls. Overall, it looked like the cases were still a bit tight in the chamber while the extractor was trying to cycle them out.

YET... absolutely no hangups in feeding or extracting. Every round went boom and the brass went flying.

Some people have told me that, since it's a new gun, it may need to cycle a few hundred rounds to smooth out the chamber, and that it wasn't anything to worry about. So I'm not going to worry about it until I feed it more ammo.

If it's still doing this after another hundred rounds, I'm going to try feeding it some plain old commercial .223 and see what happens. If it's stressing out on NATO ammo but cool with commercial .223, then I'll send it back to DPMS and have it checked. And likewise if it's gouging the cases on commercial ammo, too, since that would be an obvious overpressure issue.

But my question remains: is this brass safe to reload? Can I take a small file to take the nicks of the rims and resize the brass and expect it to feed and function normally?

I misunderstood your question. I thought you were blowing primers with pressure signs. I'm sorry but I know nothing about reloading 5.56 brass. Have you tried asking your question in the reloading area?

Not related to the problems here but, I have seen heavy crimps and excess oil in the chamber and bore cause high pressure signs also.
Almost every M193 and 855 load I have fired in the last 15 years has shown swipes but I have never had a primer fall out.

Please Tell me you are not Putting Head space gauges into a Fully assembled Weapon and allowing the mainspring tension to drive the bolt home???

Especially when the No Go Gauge did not want to close and then Closed... ...
You should have used only Slight Finger pressure on an Disassembled Flawlessly cleaned gun...
That's all you need to know if the gauges go or not... NO hard pressure... you are forcing very closely fitting HARDENED Gauges into the Chamber... not good my friend. You Can Ruin Guns doing that.

I just ran across this thread because I jammed up my rifle yesterday and it turned out to be a smashed up spent primer down in chamber hiding behind the locking lugs.

This is the 2nd time this has happened to me in about 2000 rounds, the first time the primer fell down into my trigger assembly.

I have a Ruger SR-556 so it is definitely chambered for 5.56.
I bought several 500 and 1000 round boxes of Federal XM-193 and it is mostly all I shoot.

Can I assume since the problem is infrequent, it is likely just the ammo and no fault of my rifle?

Below, normal chamber pressure and the high stress points in red and yellow. (case stretching)

http://i122.photobucket.com/albums/o254/bigedp51/deform.gif

Below, excessive high pressure caused the base of the case to expand enlarging the primer pocket allowing the primer to fall or pop out of the primer pocket.

http://i122.photobucket.com/albums/o254/bigedp51/ann1.gif

http://i122.photobucket.com/albums/o254/bigedp51/ann2.gif

Without pressure measuring equipment you can measure the base of the case with a micrometer and when this cartridge is fired if the base diameter increases more than .001 (one thousandths) it is a sign of excess pressure.

Haven't posted here in years, and we know we'll be looked upon with disdain due to the type of rifle we specialize in and work on, (we do work on ARs occasionally) but this came across my 'puter the other day and wondered if any here had read it. (?) Gun Digest Article

And clicking on the pic of the "5.56 Reamer" and ".223/5.56? gage" allows you to read more info on this guys answer to the pressure problem, on his site:
m-guns

Thoughts, questions, comments?

We're not *all* snobs...

Tolerance stacking, both in head space/throat erosion and initial dimensions due to tool wear, can lead to bad, bad stuff happening.  It seems to happen more in ARs due to the caliber and the ubiquitous nature of the gun.

 

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.