View Full Version : Blown primer causes?
Does anyone have information on back pressure from a suppressor or brake causing blown primers (presumably some sort of an over pressure situation)? I'm guessing that chamber size and/or ammo problems are causing this malfunction but want to find out if adding back pressure at the muzzle could contribute.
I've never heard of that at all in my years of silencer readings. I have my own silencers too, but I'm only a 2 year veteren to actual silencer ownership. If a primer it blowing, it's not a result of a silencer.
Thank you. I had a feeling that would be the case but want to eliminate possible variables while diagnosing the failure. It appears more likely a chamber or ammo issue. I appreciate the input!
What size is your barrel length? I ran a sbr (7.5) and had the worse problem with primers being blown out of their pockets and ending up jamming my FCG! People tried to tell me my barrel was out of spec which was not the case (had an armorer check the specs). What I ended up doing was an all inclusive makeover starting with using a M16 bolt carrier, beefed up the extractor spring, used a DPMS Heavy Buffer made for SBR/Full Auto applications (according to Brownell's) and I think that was it. It seemed to do the trick for my SBR.
If your rifle fires fine w/o the silencer, then you know it is not a chamber or ammo issue. Tell us what your rifle setup is por favor!
We are using a 16" barrel in semi only. We are testing a new compensator design and the failure occurred under rapid fire conditions. The rifle doesn't have a lot of rounds through it and this is the first time this failure has happened to it. It's only happened once but we want to make sure the failure isn't related to the comp. The math tells me that we have plenty of vent area as compared to most other commercial units so I'm relatively sure our back pressure curve is not the problem but wanted to get any input from real world experience. Theoretical numbers are nice but sometimes don't reflect what actually happens. I appreciate the feedback!
I apologize, I assumed you were using a sound suppressor (Silencer). So basically you are doing testing on a new brake/flash suppressor and you have had a primer blow out of pocket. I would place an A2 Birdcage on the rifle and see if the problem is duplicated. I'm sorry for wasting your time and I am curious to see what others think about this issue.
Good Luck!
That test is on the list. I've run many rounds through my DDM4 with no problems using our new comp so this came as somewhat of a surprise. The failure occurred with my friends rifle, I think it's a Colt. We plan to do exactly as you suggest and then repeat with the comp and see if the failure reoccurs. We think it was most likely it an ammo problem (XM193) or a tight chamber unless otherwise indicated.
moneymaker
03-13-10, 07:00
loose primer pocket,over pressure loads,round out of spec. .223 chamber and not 5.56 chamber shooting 5.56 ammo,again high pressure.
Are you using GI ammo, commercial factory ammo or reloads. If reloads how many times reloaded?
GI is crimped, commercial isn't & primer pockets stretch from use in reloads.
It happened with new XM193. We don't shoot reloads. We are relatively sure that this failure is ammo related. Just to be sure we will run a 5.56 chamber reamer through it next week and verify that everything is up to spec.
Heavy Metal
03-14-10, 13:52
It happened with new XM193.
Well, that solves that mystery. This stuff is notorious for popped primers.
That's what I've been hearing. Just unfortunate that it happened during a new component test. There are enough variables to keep track of let alone add to the list with faulty ammo.
Do you have any photos? It would help to see what the problem is.
Will get some posted asap.
If you have some of the cases you fired that day and a live round you can try this. Good luck.
If you can get a copy of the book Modern Handloading by Maj. George C. Nonte, Jr on page 108 paragraph 3 has a good explanation on chamber pressure measurement.
If you can't find a copy this is what it says.
To determine whether excessive pressures are being produced, a new, unfired case should be measured at the head, (web) and then loaded and fired, and afterward measured again at the head. If more than .001" increase in diameter, you are getting into the excessive pressure zone; and danger mounts as diameter increases beyond that limit
Ned Christiansen
03-14-10, 21:57
I don't think there's anything wrong with XM193. It or any other 5.56 NATO-pressure load will pop primers in a chamber that is something short of 5.56 NATO. Firing 5.56 NATO-pressure loads in a .223 SAAMI chamber is almost certain to result in popped primers.
5.56 ammo in .223 chambers is discouraged by many sources-- including the websites of SAAMI, Winchester, and Hornady (it's right on the Hornady box of their 75-grain 5.56 TAP load: "Not for use in .223 chambers".
This is from some recent re-testing recently done at ATK / Federal cartridge:
First and foremost, the 5.56 cartridge is a military round, designed to operate under highly adverse conditions (combat) in varying weapons systems such as all the M16/M4 variants as well as the SAW (Squad Automatic Weapon), otherwise known as M249 or Light Machine Gun. To ensure operational reliability, this round is designed to operate at significantly higher pressures, namely just short of 59,000 psi (case mouth meaured) which equates to almost 62,000psi when measured via conformal transducer.
The SAAMI max set forth for the 223 is 55,000psi (conformal transducer).
To facilitate operating under these higher pressures, a 5.56 cartridge case possesses a stronger web design (thicker case walls towards the head), reducing internal powder volume, an important consideration for reloaders.
The remaining differences are found in the chamber of the weapon (longer, larger diameter freebore and a reduced throat angle giving a much longer throat, resulting in a more gradual engagement of the bullet to the rifling).
What does all this mean? In short, you can safely fire all 5.56 AND 223 ammunition in a gun properly chambered for 5.56. You MUST NOT fire 5.56 ammunition in a 223 rifle. As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. Continued shooting of 5.56 ammunition in guns not chambered for 5.56 will show many warning signs of over-pressure, such as flattening of primers, smearing of the head stamp, dropped primers, blown primers and pre-mature wear on extractors and bolts.
The chamber reamer came in and we'll be finding out if the chamber is to 5.56 spec or not. This particular chamber has been suspect before which I was unaware of. We'll soon find out! Thanks for all of the replies guys!
I am a little confused myself. I don't know what a chamber reamer is going to do to help you check your chamber.
What you need are a set of 5.56 Nato headspace gauges. I know Forster makes a set of go/no-go/field gauges specifically for 5.56 Nato chambers and not .223.
Chamber reamers are for after re-barreling a rifle and finish reaming for setting headspace on a new short-chambered barrel. Or maybe I am missing something here.
There are reamers that open up the throat area of the chamber (ahead of the neck area) Ned C. sells one. They open up the throat and don't affect the head space. If you google it you will find it.
As for head space I don't know what happens if it is slightly out of spec?????
Ok....I read up on this reamer and why this type is used. Still, I would not be buying a $240 reamer, compared to a $25 head space gauge to see if you have a .223 chamber or 5.56 before purchasing the reamer.
Looks like a neat tool. My only experience with reamers are with re-barreling a couple of bolt actions and Garands. I have bought short chambered barrels, reaming them and using head space gauges to set the head space properly.
This tool makes it easy and is pretty damn neat.
As far as the blown primers, I am leaning towards ammo myself, any indications of "flattened" primers on the other fired cases?
Yeah $230 is a lot if you only need it once. Based on my understanding the headspace gauges don't measure beyond the case shoulder area so those gauges will not help designate between 5.56 and .223. Ned C. also has a gauge that can be used in this regard (to differentiate between 5.56 and 223) and it is around $40....it basically gauges the throat area.
PS. I have some federal lake city 5.56 from back in 2001 (lot 06, head stamp 01, no sealant). About 1-2 rounds per 20 round box have an incomplete primer crimp (about 20-30 degrees of the circumference is not crimped because the crimp is off center). It is not suprizing that this stuff blows primers on me.
Ned Christiansen
04-28-10, 09:08
Yes-- a headpsace gage tells us nothing about the neck, freebore and throat of the chamber which are much more likely to be a problem than headspace. Oddly enough I have never seen headspace be a functional problem in an AR-- maybe once, but I think never.
Freebore and throat-- much different story.
The gage I offer checks these areas and does not check headspace.... it's $44. You can see it here:
http://www.m-guns.com/tools.php
I dreamed this up because I hated there not being an easy way for a guy to check it-- yeah he can buy the reamer and check by reaming--but if it didn't need reaming that is indeed an expensive way to find out.
HelloLarry
04-28-10, 10:27
It's a Colt. I seriously doubt that it is a chamber problem. I wouldn't be cutting a chrome-lined chamber and barrel with a throating reamer either. Can't imagine a better way of ruining the barrel.
XM193?
Ammo that was rejected for military use because it is out of spec in one or more ways.
Yeah,
Sorry if I was not clear...I think this guy's rifle is fine I was just commenting on the reamer to clarify things.
I guess that's why there is an X in the XM193. It's a mystery
My understanding of the primer issue, is that almost every time it is a result of a tight chamber or bad ammo. I have never heard of a silencer causing blown primes. Thats not to say that it couldn't... I just have never heard of it.
PRGGodfather
04-28-10, 16:49
We know the chamber was tight as well as the XM factor. It measured Go and No Go, but Ned's reamer still removed material. The suspect ammo lot was removed as a factor, and there have been no recurrences.
We had three blown primers and one flattened case head all from the same lot.
What's a flattened case head?
PRGGodfather
04-29-10, 01:40
The rear of the case, where the head stamp is located, was pretty squished against the bolt face. You can even see the ejector impression. Under high pressures, the brass gets "squished."
I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi.
Do you have pressure trace graphs to go with this? I'm on board, but for many "seeing is believing" - I think that the traces would speak louder than words.
I bought an SR25 (post-ban) and had a muzzle brake installed. With the brake I started to get blown primers with a standard 308 match reload that worked fine in my M1A and marginally OK in the SR25 before the brake was added. I suspected that the addition of the brake resulted in an overgassed condition that caused the bolt to retract too early to permit the chamber pressure to decay properly. I bought and installed a heavy buffer (10 oz) to replace the original plastic buffer. Now the rifle functions fine with my 168 gr Sierra match reloads with 41.5 gr IMR4895 (caution: this load works in my rifles, but YMMV). The case heads look fine too. The downside is my SR25 is now about half a pound heavier (and it was too heavy before).
Ned Christiansen
06-23-10, 10:18
This issue with chambers having short freebore and throat can apply to .308/7.62 as well. And it can go beyond the pressure spike / blown primer issue.
How about this little true story: snipers having a range day. End of day, a sniper ejects a live round and unloads the rifle. The rifle is not cleaned that evening. The next day, more sniper training-- they are to do a stalk on instructors and fire a blank. One sniper goes to chamber his blank and it won't go. Why?
The bullet from last night's ejected live round is stuck in the lands of the very short-throated chamber. An almost perfect storm with plenty of blame to go around..... I expect this would have blown the rifle but likely killed the instructor and injured the sniper.
Back to .223 / 5.56.... acrashb, I saw your post earlier but did not realize it was adressed to me (Dept. of Duh, can we help you?). No, I don't have any graphs on this but I'll check with the guy wot did it and see if there's anything available/presentable.
...I don't have any graphs on this but I'll check with the guy wot did it and see if there's anything available/presentable.
Hi Ned - just bumping to see if you'd had a moment to check.
Ned Christiansen
08-25-10, 21:20
My friend sent me some data on this but at a glance I could not understand it-- let me try and revisit it.
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