I was checking sights on some rifles this morning, and finally grabbed the AR. The ammo for that rifle is 63 gr Sierra SMP, and I have a few rounds left from when I used CCI BR4’s, so I’d use them first. Well, I guess that the BR4’s do have a softer cup, because the AR ran off about 5 rounds in a full auto runaway. Switched to the 41’s and had no problem. The round that was unfired in the chamber, when I cycled it out, had a small dimple in the center of the CCI 41 primer.

Never had that problem before. Would cold weather have anything to do with what happened?

For the inquisitive, during the runaway, only round 1 went into the 1” bullseye. Rounds 2,3,4, and 5 went elsewhere. up, I will assume.

I'll be interested to hear theories from others. I've never used the CCI 41 and never had an issue but that would scare the chit out of me.

I've always used 400's and 450's for semi auto ad never experienced a slam fire. I have seen marks on unfired primers after clearing the round.

There certainly would be a pucker factor in it happening though.

Dang 603, I bet that got your full attention! I’ve used an assortment of primers for AR as well but no slam fires. I’ve only had an AR for a little over one year and don’t have anything to add other than like big fitz, I’m interested as heck in what those who may have had similar experiences have to say.

Poached this from Midway.

"Number 41 Mil-spec primers are made to the same specifications of the U.S. Military and reduce the chances of a slam-fire. While designed for you in Military-style semi-auto rifles, they use the same data as CCI magnum primers."

So what's the difference of CCI# 450 & CCI# 41?

I've read that the difference is the CCI 41 primer uses a different shaped anvil, more "dome" shaped, more rounded than a "standard" CCI primer's anvil, to help eliminate "slamfires".

There are other questions and things to look at beside just primers. Is the bolt & carrier assembly clean? Firing pin channel is free of crud and FP freely move in the channel? Could there have been a primer pop out and fall in your lower effecting the trigger/disconnector? Do you have a "match type" trigger system installed?

I posted this a couple of weeks ago on primers, its's on page 2.

Note this comment: "CCI #41 - commercial version of the fully-qualified DOD primer for use in U.S. military ammo. With this primer there is more 'distance' between the tip of the anvil and the bottom of the cup than with other CCI SR primers. .025" thick cup. Same primer mix as CCI 450."
The following is from this link. Read, use, and follow all safe reloading practices.

http://www.sksboards.com/smf/index.php?topic=56422.0

Small Rifle Standard

CCI 400 -thin .020" cup, not recommended for AR15 use by CCI/Speer. Good for .22 Hornet, .30 Carbine. See Note 1 at the bottom of the page
CCI BR4 - match primer with a thicker .025" cup.
Federal 205 - Mil-Spec cup thickness according to Federal - okay for 5.56mm. .0225" cup thickness.
Federal 205M - same as the 205 but the match version.
Magtech PR-SR - .025" cup thickness (not much feedback yet on this new primer as to AR15 suitability but with the same cup thickness as the Rem 7 1/2 it looks good so far)
Remington 6 ½ - thin .020" cup, intended for older, lower pressure rounds Remington says do not use for the .223 Rem or other similar pressure rounds. Good for .22 Hornet, .30 Carbine.
Remington 7 ½ BR - A match or "bench rest" primer. Lyman & Nosler classify this primer as a Standard. Remington says the compound is the same as the 6 1/2 but with a thicker .025" cup.
RWS 4033
Winchester WSR - some piercing issues noted when changed from silver to brass cup. Cup thickness is a bit thinner at .021". Most say they are good to go for the AR15 despite that, probably because of the hardness of the cup. Some feel they are less resistant to higher pressures.
Wolf/Tula Small Rifle SR #KVB-223 - soft, sensitive copper cup, not recommended for AR15/military rifle use or high pressure rounds.

Small Rifle Magnum

CCI 450 - same thicker .025" cup as the BR4 and #41.
CCI #41 - commercial version of the fully-qualified DOD primer for use in U.S. military ammo. With this primer there is more 'distance' between the tip of the anvil and the bottom of the cup than with other CCI SR primers. .025" thick cup. Same primer mix as CCI 450.
Remington 7 ½ BR - A match or "bench rest" primer. Hornady, Handloads.com, and Chuck Hawks classify this primer as a Magnum, differing from other sources that classify it as a Standard. .025" cup thickness.
Wolf/Tula Small Rifle Magnum SRM - hard, less sensitive brass cup intended for AR15/military rifle and high pressure rounds - #KVВ-5,56M.
Wolf/Tula Small Rifle 223 SR223 - #KVB-223M "This is the newest primer available in the Wolf line. It is ever so slightly hotter than the small rifle magnum primer and it comes with a brass colored thick cup. This primer can be used in place of the SRM primer or used when a different powder is used that is hard to ignite."

Primers recommended for use in .223 Rem/5.56 semiautomatic rifle loads:
CCI #41, 450, BR4 (#41 & 450 good with ball powder)
Federal 205, 205M
Remington 7 1/2 BR (good with ball powder)
Winchester WSR (good with ball powder)
Wolf SRM (good with ball powder)
Wolf SR223 (hotter than SRM - great with ball powder)

WOLF/TULA PRIMER APPLICATION CHART FOR ALL PRIMERS - http://www.mpzflame.ru/production/primers/
Wolf and Tula are two of the common U.S. marketing names of primers made by Murom (OJSC «Murom Apparatus Producing plant» "For many years, our constant partners are «The Tula Cartridge Works», «Barnaul Cartridge Plant» and others.").

Today I’ll clean the AR and relube. It’s the direct impingement version, and I haven’t cleaned the BCG recently. J Hill’s info is excellent, and reminded me that I might have used some CCI 400 primers instead of the BR4’s. That might explain the slamfires. I’ll have a look at some loaded rounds and see if they are the 400’s or the BR4’s.

Like I said earlier, I switched to the 41’s in the last reload session (last week) when loading for the AR.

Just to mention it, the powder I use is H335, and some folks suggest magnum primers with that powder. The 41’s are considered magnum primers, so I checked POI at 100 yards with BR4 loads and 41 loads and did not see any noticeable diff in bullet POI.

And I’ll do some post-cleaning target practice with one in the chamber and one in the mag. We’ll see if I get another slam fire.

The primers in the slamfired rounds did have the CCI 400 primers, which are not recommended for use in the AR. Those rounds were the last of rounds loaded originally for the bolt gun. I think I found the problem.

Not sure why someone would recommend a magnum primer for H-335. It's a pretty quick burn rate, and also one I use on. 223 for AR-15.

Good to know the CCI-400 are a no-go for AR-15. Thank you for sharing that info.

This is interesting. I have used CCI 400's in my .223 Rem, 223 Wylde, 224 Valkyrie, and 300 HAM'R and have never experienced a slam fire. Can't figure out what happened in 603Country's frightening experience, but that will sure get your attention!

The only time I had slam fires was my own fault for not having the primers seated properly. Not deep enough. If you can set the round on a flat surface and it wobbles on the primer (my mistake at the time) bad things can happen in AR platform. May not have been remotely 603s issue but was mine. Learned that lesson a long time ago as a newbie hand loader.

The whole thing is interesting. Prior to the runaway, I had fired off a few rounds, all with the CCI400 primers, all single shots with no problem. Then the runaway, which didn’t empty the mag, and left one round unfired in the chamber. That round had a slightly dimpled primer, but that was to be expected. So, the runaway consisted of some, but not all, of the rounds in the mag. Why not all? Why not none?

I’m out of CCI400 primers, and from now on will use CCI 41’s, or on occasion BR4’s, so the problem should not happen again. And I’ve cleaned and examined the BCG, relubed, and have shot the rifle with the CCI 41 primed rounds.

The BCG was a bit dirty, and there was some carbon on the bolt, but the firing pin moved freely. Nothing looked out of the ordinary.

I’m sure glad this happened at the shooting bench, with the rifle wedged into the big sand bag (Uncle Bucks). When I get into the deer blind, that’s when I hit the bolt release. It would have been bad to machine gun my deer blind and while enclosed.

yikes! I hear people talk about slam fires but I've never actually experienced one myself. I regularly use 400s for 5.56 and 300 BO on the AR platform. I find it even more interesting that it wasn't just a single slam fire, but a series of consecutive slam fires...that's some crazy sh$t... What BCG are you using in that gun?

Now you must delete this thread immediately, before the ATF reads it and decides that CCI400's can turn a semi auto into a full auto and thus qualifies for additional regulation LOL J/K

Based on what you've said and considering the fact that your BCG passed muster, I'd suspect that you had a couple of rounds that the primer was not quite seated all the way to "flush." And it didn't dump the mag completely because the rest of the rounds, or the single round you still had in the chamber, was seated flush. It got a light strike from all that bolt slamming, auto-firing activity, but not enough for detonation.. Glad you, and everyone around you were OK. It would take a couple of trips through the HEAVY DUTY cycle in the washing machine to get the skid marks out of my skivvies, for sure!

Never had it with an AR but a 89 dollar SKS emptied the last 6 shots full auto style one afternoon.

Supposedly, ball powders ignite better with magnum primers. CCI and Win 41’s are magnum primers.

I’m sure 400’s aren’t the best for AR-15’s, but I’m don’t think I have it in me to get rid of the 5k I still have. CCI 41’s are fairly easy to find now so I’m going to start buying them instead.

I have some more info regarding the CCI 400 primers. You might find it interesting. This morning I took a good close look at the remaining loads with those primers and the loads with the CCI 41 primers. The problem, it appears to me, isn’t specifically that of the CCI 400 primers, but possibly more the fault of my RCBS primer seater. The cases used were new or once fired Lapua and have tight primer pockets. Seating the primers with the seating tool noticeably flattened the softer CCI 400 primers cups, but not the CCI 41’s. I wonder if the slightly flattened cup of the CCI 400 primers would cause them to be more prone to a slam fire. I’m thinking that it would.

I agree. It gets the cup closer to the anvil.

Couple years ago I went to the RCBS bench mount primer sister, away from the hand held.

Primer pockets got tighter is certain brands of brass, I am sure of it.

Lots more leverage getting primers seated, and I have not crushed any.

Little late to the discussion, but it's always been my understanding too that the 41s have a little tougher (thicker?) cup making them more resistant to slam fires. Not Gospel, but but just what I've always been taught in the AR reloading circles I frequent. I've always had it beat into me to only use the 41s for ARs.

I have loaded and shot over 5K .223 with CCI 400 in ARs. ( My old Speer manual recommended them or the 450 with certain ball powders ) I know the count because I ordered a case and used them up. I switched to the #41 just because it was "recommended" I have fired 4K of them now. Never a slam fire out of a Colt HBAR, RR HBAR and 2 RR CARs or a Ruger mini with either flavor. I uniform the primer pockets and swage any military crimps on a Dillon Swage, you only have to do it once. I check at all finished rounds for high primers. I prime on the Dillon 650 and you can feel primers seat. Yes some flatten a little if you really lean on the handle but I have never had a slam fire even then.

Interesting side, on the 50 BMG I recall that you have to flatten some brands of primers to make them sensitive enough to light off. I don't load for this cartridge so someone with experience may have to provide context.

I would be more likely to believe high primers before anything else. I have at times been negligent on cleaning my BCG so discounting this as a reason.

I have 5K of the Rem Benchrest 7 1/2 that I heard were good to go but have not broken into that case yet. So I have nothing to share regarding them.