Finally a jam... Colt 6920

[Dr.Rob]

...after 3000 or so rounds and I think it was my fault.

Last COF of the day shooting standards. I didn't fully seat a P-mag, it dropped out into the dirt while prone and instead of shaking the crud out of it I snapped it back into the rifle. I had two failure to go back into battery in a row.. Tap rack bang 2x, finished the COF.

Back on the bench ran a q-tip around the feed ramps and cleared out a good clump of dirt/grit. No damage to the bolt head or lug recesses so it was a dirt clod not a rock.

Ran a couple magazines after and no issues. Dumped a teaspoon full of dirt out of a P-mag when I got home. Hmmm.

We'll see how she does the next 3000.

 

[rcmodel]

You doing a torture test or what?

rc

 

[Robert]

NA he was at the Tactical Rifle Match in Pueblo West... I missed it.

 

[Dr.Rob]

I do clean it every 2-300 rounds. So not really a torture test.

 

[BikerRN]

I ran a 2500 round test on my 6920 twice.

The only thing I did was add some oil at intermittant intervals. I have yet to have a malfunction with my rifle. This "test" convinced me of the platform. As to the caliber it, 5.56/.223, is the original caliber for the platform and since I believe that most guns shoot best the caliber they were designed around I will refrain from changing the caliber. If I want to shoot a different caliber I'll get a different platform, for now at least.

BikerRN

 

[Robert]

I finally had a stoppage 2 weeks ago at the range re-zeroing my rifle for the match I missed... I was up to near 1000 rounds when a primer came out and managed to work it's way down under the trigger assembly. Full stop. Brought it home, I did not have my tools at the range, and fixed it in 5 mins.

 

[JustinJ]

I'm about 500 rounds into my 6720 without a single issue. About 150 of those round were with a can.

 

[Dr.Rob]

I ran 200+ rounds through a can on mine. No issues but holy cow, did it get dirty.

Gus:

We had a shooter that kept blowing primers so bad he locked up his action: trigger wouldn't pull, safety wouldn't move, hammer frozen. All from primer trash.I'm not sure what brand his rifle was but it required a trip to the bench with someone that had tools handy to get it up and running again.

 

[Al Thompson]

DR, IMHO and IME, that's usually a case of a .223 chamber or chamber out of spec. Less often, it's bad ammo - ammo loaded too hot or poor reloads.

My CMMG upper, Stag lower is on it's 3rd case of ammo, no issues and only wiped down.

 

[Robert]

he locked up his action: trigger wouldn't pull, safety wouldn't move, hammer frozen.

That is what happened to me. It gets down unfed the safety and you can not pull the trigger or rotate the safety. Now I have tools in the bag. A simple Allen wrench to get the grip off and a punch to knock the pins out and you are back in business. I have never had something lock up so bad. I am thinking of getting one of those dividers that will keep trash from getting down in there again.

Come to think of it, it was one of Justin's reloads...

 

[Dr.Rob]

Al, it was definitely his reloads. Something just wasn't right in his combination of powder and brass and THAT rifle.

Watched his brass on his final string. Blew out every primer 5 of 5.

 

[Creature]

Forgive my ignorance...I am not familiar with what is going with blown primers. I have never heard of this. What is happening when a primer blows out? Is it happening while the bolt is out of battery, in battery,...locked or unlocked?

 

[4v50 Gary]

I've had stoppages in my Colt, but then again, when you use cheap ammo and magazines, that's to be expected. Failures are training opportunities but in real life situations, use the best (proven and tested) ammo in the best magazines (tested and proven too) you have.

 

[Dr.Rob]

Primers blowing out is a sign of overpressure in a reloaded case.

The most likely culprit is too much powder.

Often military brass has thicker walls than commercial brass therefore less volume inside. What a load book says is max for say, commercial brass by Remington may not apply to a mixed lot of Lake City and NATO headstamped brass. This is why when you develop a rifle load you try to use 'all the same brass' and give them a visual inspection before seating the bullet.

Flattened, backed out, cratered, pierced and blown primers are all signs to look for when devoloping a good consistant safe and accurate load. They are ALL signs over overpressure. These things also have to 'make your rifle work' in the case of a semi-atuomatic as oppsed to a bolt gun. They must be full length sized in most cases where a load developed for a specific bolt gun could be neck sized only then trimmed to length.

I don't think I've ever seen a blown out primer from factory new ammunition.

A 'too tight' chamber ie an old .223 spec chamber as oppsed to a looser milspec 5.56 chamber could be a part of the equation here but I suspect its simply too much powder.

 

[Al Thompson]

too much powder.

Probably right. One other issue can be loose primer pockets. Though at the rate you guys were popping primers, suspect not.

 

[Mr. Happy]

I guess I picked the right first rifle! Hope my next one is as reliable. What it will be, I don't know - a new upper, an AK, a 308....

 

[Justin]

Al, it was definitely his reloads. Something just wasn't right in his combination of powder and brass and THAT rifle.

Watched his brass on his final string. Blew out every primer 5 of 5.

Evidently the powder he was using is very temperature sensitive, and will start to blow primers when the gun gets hot.

His reloads would probably work fine for a bolt-action varmint gun, not so much for a rapid-fire rifle stage.

 

[Surf]

Locking up the rifle is not the worst result of blown or popped primers. Full auto when your not expecting it can be much worse.

 

[Still Shooting]

Change the Powder?

Might be a good situation to load with IMR 8208 XBR - Awesome temperature stability! -I don't shoot .223/5.56, but find it to be pretty accurate in my .243win and .257roberts loads, and the published temperature numbers would likely prevent powder changes with a hot rifle...

I got interested after talking with a benchrest guy at my local club. Bought a pound, and tried it in several calibers. Nice powder!

 

[Cosmoline]

I intend to take my Gov't Carbine out this winter in sub zero temps, expose to the air the whole way there and see how it does. So far it's been incredibly reliable.