View Full Version : Blown primer...what next?
nightchief
07-05-17, 12:04
Not really sure which sub forum this belongs in...mods, please move if needed.
On Monday (July 3), I was running my SBR suppressed when it locked itself up tight. Bolt Carrier was unmovable half way into the RE and half way into the upper receiver. To get the BCG loose, I ended up removing the RE and knocking the bcg forward softly when a primer dislodged itself. This fixed the malfunction, but now I have concerns about the over pressure that occurred and what may need to be tweaked to avoid this happening going forward. It's possible it was a one off issue with one bad cartridge, but I have had a few issues running this particular cartridge with this set up. The intent with the rifle was for it be usable for HD, but this latest issue has me regulating this upper to range use only. Its kind of expensive for a range toy. :( I've got probably 600ish un-suppressed rounds fired using a wide variety of ammo and no issues since some initial fit trouble causing FTF's.
Set up is 11.5 CL barrel with .070 gas port, carbine gas system; non adjustable gas block; mil-spec carrier; A5 RE with A5H2 buffer; Surefire 556-212 suppressor. This occurred using IMI M193 from an Okay 30 rd magazine.
I would like to be able to reliably shoot 556 77gr OTM type ammo suppressed. I would also prefer not to use an adjustable gas block. Looking for advice on what adjustments to make now. H3/H4 buffer? Different carrier (like LMT-E or Gemtech adjustable)?
NC
As I think about your description of events, it seems like blowing primers is unusual for this rifle which makes me think it is over charged ammo that is causing your malfunctions. You said you had other problems with this batch of ammo as well. I got a bad batch of IMI ammo recently that blew primers and caused my KAC to lock up in a similar way to what you describe. I sent it back and the gun functions smoothly with a wide variety of good factory ammo and hand loads. I shot it 4 or 5 times with no issues before my confidence in the gun for HD applications was regained.
Gas port can be removed from the conversation. You're good there. I'd bet the ammo is to blame. I'd try black hills 77s in both 556 and 223 loads.
There is an outside chance your chamber needs reaming. But I think it's the ammo.
Has all the brass been inspected for blown/loose primers?
Odd are low that ONE primer will lock up the gun. Most likely several came out and one got lucky.
Where did the primer get stuck?
nightchief
07-05-17, 15:39
Has all the brass been inspected for blown/loose primers?
Odd are low that ONE primer will lock up the gun. Most likely several came out and one got lucky.
Where did the primer get stuck?
I checked all the cases I could find, and never found any with a missing primer. Primer was lodged between the carrier and upper receiver somewhere. Carrier was stuck to the point of needing to tap it out with a mallet...when it came loose, the crushed primer fell on the ground, so I'm not sure exactly where it was lodged. Some additional info, outside temp was about 95 degrees, and I had run two, 20 round mags through it suppressed. No mag dumps, but with some multi round, high speed shots. I had run quite a bit of GECO 223 and PMC bronze before hand with no issue. When I went to the IMI 556, this occurred on the 2nd or 3rd round after changing mags.
nightchief
07-05-17, 15:43
Gas port can be removed from the conversation. You're good there. I'd bet the ammo is to blame. I'd try black hills 77s in both 556 and 223 loads.
There is an outside chance your chamber needs reaming. But I think it's the ammo.
That was the supposed to be the next ammo to run after the IMI, when the gun locked up. I will definitely try the BH 77 gr next. Perhaps some Fed Gold Metal Match 77gr SMK too.
It can happen, the question is whether or not it's happening more than once. I would try other ammo just to make sure it's not something else.
Odd are low that ONE primer will lock up the gun. Most likely several came out and one got lucky.
I'd guess that half of the primers I've had blown in our ARs will end up in a really shitty spot. The have a magic way of getting into the worst possible places.
Spin Drift
07-05-17, 21:06
Had one end up in the FCG, turned an SR-15 into a Jam-O-Matic, had to bust open the lower(push pins and trigger/hammer/selector…) to get the primer out, wasn't visible.
vicious_cb
07-05-17, 21:08
I'd guess that half of the primers I've had blown in our ARs will end up in a really shitty spot. The have a magic way of getting into the worst possible places.
Blown primers, even a single one are magnetically attracted to the fire control group. It's one of the laws of physics or something.
Sounds ammo related to me. The IMI that I have shot seemed hot to me, and wasn't very accurate in my rifle. I know some have had success with it, but not me when I tried it. Purely unscientific observation on my part, but that's my impression of it.
Blown primers, even a single one are magnetically attracted to the fire control group. It's one of the laws of physics or something.
Yup, blown primers are bad juju.
That's why crimped primers are a real good idea and give some measure of insurance.
The can pin Area sucks. If they get in there, the gun can be completely locked up.
Aren't the primers crimped on that IMI ammo? Most of their product line has crimped primers. It was my understanding a stray primer is a result of loose primer pockets whereas a popped/pierced primer is indicative of overpressure. One can experience stray primers without having pressure issues but I agree some of the IMI ammo seems fairly hot.
Primers pop out when there is less case support by the bolt face with the residual casing pressure blowing them out for their tension and a casing head distortion situations that reduce the proper tension between them. Higher peak pressures do not help this.
There's a few things that we can look at here, and a few remedies.
Aren't the primers crimped on that IMI ammo?
Crimp depth and tension varies widely. I've had some xm193 brass where I could re-prime it without even removing the crimp. Whereas other types of brass/crimps can be really stout.
While that blown primer probably has an an ammo component to it, I would bet that Ned's reamer would fix it.
nightchief
07-08-17, 15:32
I've ordered one of Ned Christiansen's 223/556 chamber gage to check the chamber. Will go from there depending on what I find out. Thanks to all on this thread for your info and shared knowledge.
NC
Primers pop out when there is less case support by the bolt face with the residual casing pressure blowing them out for their tension and a casing head distortion situations that reduce the proper tension between them. Higher peak pressures do not help this.
There's a few things that we can look at here, and a few remedies.
If this was the case wouldn't this be happening all the time with different types of ammo?
nightchief
08-12-17, 23:22
I tested the barrel with the Ned Christiansen gauge and I thought the chamber might be slightly on the tight side. I sent the barrel (entire upper) to the manufacturer for their inspection. The manufacturer felt the chamber was within spec. They also test fired it using IMI M193 that I supplied from the same lot, as well as Federal XM193 and had no failures either suppressed or unsuppressed. I have since checked another 11.5 " barrel chamber and the gauge was snug in that one also. I have had no issues with this barrel when running suppressed.
I fired approx 100 rounds of GECO 223, CBC M193 and CBC 62 gr 556 suppressed without issue. All of this ammo was fed from Gen 3 PMAGS. Perhaps one bad round is what I encountered. I will continue testing the upper suppressed and try out some CBC 556 77 gr OTM and BH 556 77 gr OTM or TMK and see how it performs.
As a side: Manufacturer was very good to work with on this issue. I had a good conversation with the owner (I think) about the testing they did. At this point, I guess I'll feel comfortable with the upper if I can get 1K+ through it suppressed without issue.
NC
Lots of folks complaining that IMI's loading their ammo too hot. Independence M193 is supposed to be loaded by IMI and its got a reputation for blowing primers as well. This is one of the reasons you crimp 5.56 amo so when the crimp fails to keep them in you've got to question the pressure.
nightchief
08-17-17, 01:44
I'd prefer that the problem is ammo related, though I have quite a bit of the IMI M193. I've read about the Independence 5.56 being hot and blowing primers and sometimes worse. I've not read (until now) about the IMI M193 having an issue with over pressure. I have stopped using this ammo with the suppressor. Additional dependablitly and function testing will be with Federal XM193 and CBC 5.56 62, CBC M193, CBC 556 77 OTM and BH 5.56 SMK/TMK. If there are no further issues, I'll be satisfied its the IMI ammo.
NC
I don't know about that, but I have fired lots of IMI ammo with no issues. The Federal Independence was way too hot and I know of a few instances of it going kaboom in guns.
Lots of folks complaining that IMI's loading their ammo too hot. Independence M193 is supposed to be loaded by IMI and its got a reputation for blowing primers as well. This is one of the reasons you crimp 5.56 amo so when the crimp fails to keep them in you've got to question the pressure.
I have not had good luck with IMI Independence ammo. The blue and white boxes. In 5 boxes couldn't get through 2 - 3 rounds without a problem. Rifle was a stock Colt 6920 that had no issues prior to using this ammo. Which is why now I'm hesitant to buy IMI surplused OTM ammo
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