Ar's have a free floating firing pin. The firing pin touches the primer every time a round is chambered. You can generally see a small dimple in the primer if you chamber a round and clear it. The firing pin was designed to have low enough mass that it should not set off the primer when going into battery. However out of spec parts, or dirty firing pins can cause slam fires like an open bolt machine gun with a fixed firing pin. Due to the free floating firing pin cci reccomeds using 450 or #41s as they have thicker cups. And the 41 has a modified low sensitivity anvil, both of which help prevent slamfires.
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Full auto runaway
- Thread starter 603Country
- Start date
603Country
New member
For a couple of years all I used in the AR were the BR4 primers (thick primer cup), and I had no slam fire problems. Then, when our reloading parts became hard to get, I decided to use up the CCI 400 primers and save the BR4’s for later. The CCI 400’s worked fine in the bolt gun and I already knew that the load (previously loaded with BR4’s) was excellent in the AR. So I moved the new loads with the CCI400 primers over to use in the AR. I shot 6 rounds in the AR with no problem and then had the full auto runaway. All the other similar loads have the CCI41 primer, and I tested them and they were fine.
I am very sure that my problem was the softer primers in the AR. I had read that the softer CCI primers were not recommended (by some) in the AR, but managed to neglect that info - senior citizen memory.
41’s from now on.
I am very sure that my problem was the softer primers in the AR. I had read that the softer CCI primers were not recommended (by some) in the AR, but managed to neglect that info - senior citizen memory.
41’s from now on.
I have used cci 400, winchester small rifle, and federal small rifle in my ar with no issue. I was told it was a bad idea. I called cci to ask. What they said was what I stated. Reccomend 450 or 41s. They also stated that it can vary from gun to gun and 400s may be ok in some guns. They reccomended taking the gun to the range and, while safely pointed down range, chamber a round and checking the size of the bird peck in the primer after chambeting. If it was pin point you were probably ok. If it was anything more probably a bad idea. But it was a gun by gun kind-of thing, and would not give any guarantees. The gun could be just fine and within allowable tolerances, just not tolerant of soft primers. Could the gun be out if spec? Possibly. Could the gun be tuned to use 400s. Probably. But when #41s seem reasonably available and others are not, why?
bacardisteve
New member
Ive fired thousands of 223/5.56 with cci 400 through atleast 10diffrent ar15s both rifle and pistol and the only time I had something like that happen it was the gun. My Issue was the pin had walked halfway out.
603Country
New member
Note that I had fired off 6 (or more) CCI400 primed rounds in single shot prior to the runaway. Must be a borderline issue. And I’m out of CCI 400’s anyway.
I’ll take the BCG apart again this morning and dry off the firing pin, which at present has some Slip2000 lube on it. Other than that, I’m not doing anything else to the rifle except taking it pig hunting.
I’ll take the BCG apart again this morning and dry off the firing pin, which at present has some Slip2000 lube on it. Other than that, I’m not doing anything else to the rifle except taking it pig hunting.
This may not be of use to you, and it may be a bad idea, but when I clean my ARs I clean the firing pin and all components of the bolt carrier group, then apply a little Lubriplate 130 grease to the firing pin shank before putting it into the bolt. This is the same Lubriplate 130 I use on the Garand.
My thinking is that the grease might slow down the firing pin enough to forestall a slamfire, but certainly not enough to interfere when hit by the hammer.
I need to add that I clean the firing pin / bolt / carrier every time I'm done shooting for the day, even if I only run one clp-wet patch through the bore. If I failed to clean the firing pin for a few range trips it would probably get gunked-up.
In my midrange prone 'spacegun' I use BR4 primers. It is single load / single fire so the bolt gets dropped from locked back for each round (with the muzzle pointed downrange) with no problems.
The only slamfire I've ever had was with a Garand and HXP surplus ammo - because I was clumsy and didn't ease the bolt far enough forward before letting it go.
My thinking is that the grease might slow down the firing pin enough to forestall a slamfire, but certainly not enough to interfere when hit by the hammer.
I need to add that I clean the firing pin / bolt / carrier every time I'm done shooting for the day, even if I only run one clp-wet patch through the bore. If I failed to clean the firing pin for a few range trips it would probably get gunked-up.
In my midrange prone 'spacegun' I use BR4 primers. It is single load / single fire so the bolt gets dropped from locked back for each round (with the muzzle pointed downrange) with no problems.
The only slamfire I've ever had was with a Garand and HXP surplus ammo - because I was clumsy and didn't ease the bolt far enough forward before letting it go.