Floating Firing Pin Slam Fire

[FredHammer]

In researching SRP, I came across the old repeated warning about AR platforms needing thicker cupped primers to thwart the dreaded slam fire potentiality. Is there even one documented/verified instance of a slam fire happening in an AR because of the use of regular SRP?

I think about how many millions of .223 factory rounds (Not 5.56 NATO with thick/hard primers) have been fired through AR15s in the last 30yrs. Nobody ever says you can't shoot .223 ammo in an AR15. However, when the question directed at hand loading, it's "OMFG, better use those #41s or you'll blow your face off!" Also to consider is the service rifle competition shooters. They aren't all using #41 primers, are they?

 

[FatBoy]

In 22 years of shooting with highpower shooters (I hung up three position 15 years ago) where Fed205ms are (were?) a commonly used primer and competitors push the envelope on loads, I have never seen, nor do I know anyone who has had a slam fire in an AR-15/AR-10 platform.

I’ve heard the stories, but I also hear them about Garands and M1As.

Not saying it can’t or doesn’t happen, and my experience is my own, but I’ve never seen it.

Now, hero trigger in rapid fire… guilty as fuck right here….

 

[srt-4_uk]

It can happen. I'm all instances I've seen/read, it was also with an ultra light carrier and a steel firing pin. Titanium firing pins were all the rage in 3 gun for this reason.

 

[pmclaine]

I've ejected live rounds from my semi autos - Garand, M1A, AR - often there is a witness hit on the primer from the firing pin but never have they gone bang.

I say "often" because I only notice it when I think to check.

 

[FredHammer]

I've ejected live rounds from my semi autos - Garand, M1A, AR - often there is a witness hit on the primer from the firing pin but never have they gone bang.

I say "often" because I only notice it when I think to check.

Oh yes, seent that a many times with that unchambered round.

 

[FredHammer]

It can happen. I'm all instances I've seen/read, it was also with an ultra light carrier and a steel firing pin. Titanium firing pins were all the rage in 3 gun for this reason.

Can you provide the link or supporting evidence? Not being snarky, but this is an example of the lore surrounding this topic.
Even if you said you saw it, that direct witness account works in my book. I'd like to hear the details of the occurrence.

 

[xsn10s]

I've used Fed 205's in my AR's for decades, and yes I've seen the primer marks on chambered rounds. I personally haven't seen a slam fire.

 

[308pirate]

I've used Fed 205's in my AR's for decades, and yes I've seen the primer marks on chambered rounds. I personally haven't seen a slam fire.

Same. Remington 7 1/2 as well.

 

[308pirate]

In researching SRP, I came across the old repeated warning about AR platforms needing thicker cupped primers to thwart the dreaded slam fire potentiality. Is there even one documented/verified instance of a slam fire happening in an AR because of the use of regular SRP?

I think about how many millions of .223 factory rounds (Not 5.56 NATO with thick/hard primers) have been fired through AR15s in the last 30yrs. Nobody ever says you can't shoot .223 ammo in an AR15. However, when the question directed at hand loading, it's "OMFG, better use those #41s or you'll blow your face off!" Also to consider is the service rifle competition shooters. They aren't all using #41 primers, are they?

It's not an issue. I have much the same experience as @FatBoy

 

[xsn10s]

Same. Remington 7 1/2 as well.

Good to know. I dipped into my Winchester white box primers and they've been fine also. However I have no issue with those who wish to use "AR" primers for an extra level of safety.

 

[redneckbmxer24]

I haven’t ever seen or experienced a slam fire with an AR platform and have shot a lot of rounds with soft cup primers.

The only slam fire I’ve ever seen or experienced was with an M1 carbine. I charged it and it smoked a round into the ground a few feet in front of me.

 

[srt-4_uk]

Can you provide the link or supporting evidence? Not being snarky, but this is an example of the lore surrounding this topic.
Even if you said you saw it, that direct witness account works in my book. I'd like to hear the details of the occurrence.

AR Firing Pins ……. what are you running and why?

Hi Everyone After participating in a thread with a few other people about trying to suss out a problem with my AR doubling ( or possibly in this case , slam firing ) . We started talking about replacing my full mass firing pin with a titanium firing pin to reduce the mass and possibility of a sla...

forums.brianenos.com

This is the first one I found. Many more around enos. Witnessed one in person but since it wasn't me behind the trigger, can't confirm it wasn't a trigger malfunction.

@TonyTheTiger might also have seen it happen. ROs see strange shit all the time

 

[308pirate]

AR Firing Pins ……. what are you running and why?

Hi Everyone After participating in a thread with a few other people about trying to suss out a problem with my AR doubling ( or possibly in this case , slam firing ) . We started talking about replacing my full mass firing pin with a titanium firing pin to reduce the mass and possibility of a sla...

forums.brianenos.com

This is the first one I found. Many more around enos. Witnessed one in person but since it wasn't me behind the trigger, can't confirm it wasn't a trigger malfunction.

@TonyTheTiger might also have seen it happen. ROs see strange shit all the time

An AR-15 with standard bolt carrier group components doesn't need extra hard primers or is at risk of slam fires.

When you queer it out with a bunch of lightweight, non-standard crap then all bets are off.

 

[xsn10s]

Hmm well it's good to know about the low mass firing pins. I tend to stick with USGI/ standard parts except for the trigger. I have a very old Armalite match trigger. More like a "duty" style trigger that's non adjustable.

 

[308pirate]

Hmm well it's good to know about the low mass firing pins. I tend to stick with USGI/ standard parts except for the trigger. I have a very old Armalite match trigger. More like a "duty" style trigger that's non adjustable.

You'll be fine. The trigger has nothing to do with the issue.

 

[srt-4_uk]

An AR-15 with standard bolt carrier group components doesn't need extra hard primers or is at risk of slam fires.

When you queer it out with a bunch of lightweight, non-standard crap then all bets are off.

Which is exactly what I said in my first post.

 

[308pirate]

Which is exactly what I said in my first post.

I'm repeating it for the benefit of others

 

[xsn10s]

You'll be fine. The trigger has nothing to do with the issue.

I never said it did.

 

[OkieMike]

I sat down and read Sierra's treatise on service rifles yesterday. The issue of primers and slam fires was addressed. My takeaway was the majority of slam fire issues resulted from a combination of factors and not just "soft" primer cups...

• M1/M14 platforms were more prone than AR's
• primers not seated flush or below the base
• single feeding rounds outside of the magazine and letting the bolt slam them into battery.

Probably a few more that I can't remember without referencing the material again.

Could it happen? Sure. But it seems like following safe reloading practices and operating the rifle responsibly mitigate most of the risks.

Mike

 

[FredHammer]

I sat down and read Sierra's treatise on service rifles yesterday. The issue of primers and slam fires was addressed. My takeaway was the majority of slam fire issues resulted from a combination of factors and not just "soft" primer cups...

• M1/M14 platforms were more prone than AR's
• primers not seated flush or below the base
• single feeding rounds outside of the magazine and letting the bolt slam them into battery.

Probably a few more that I can't remember without referencing the material again.

Could it happen? Sure. But it seems like following safe reloading practices and operating the rifle responsibly mitigate most of the risks.

Mike

What sparked my OP was the Ginex primers. I was only able to get the regular/non #41 type.
The Ginex are .0025 shorter than the #41 primers. So, out the gate they seat deeper in the primer pocket.
Also, the Ginex seem to be harder cupped anyways. Both Ginex and #41 are same diameter, but the Ginex will shave a sliver of the cup while the #41s will deform to fit in the swaged 5.56 brass.

 

[308pirate]

• single feeding rounds outside of the magazine and letting the bolt slam them into battery.

I did that thousands of times without issue

 

[PappyM3]

Can you provide the link or supporting evidence? Not being snarky, but this is an example of the lore surrounding this topic.
Even if you said you saw it, that direct witness account works in my book. I'd like to hear the details of the occurrence.

A guy in my company supposedly had a slam fire when chambering his M16 SDM-R in the back of a Bradley before patrol.

I say supposedly because we all just thought he had an ND with the match trigger and didn’t want to get in trouble.

I’ve personally never seen or experienced an AR slam fire in the military or on the firing line at CMP Service Rifle matches. And those matches are chock full of people using soft primers and may or may not be seating the primers fully.

Still, whenever I chamber a round in a gun, I do so with the barrel pointed in a safe direction.

 

[bigjake83]

Every season like clock work I burn through one 6.5CM barrel 2500-3500 rds, and every other season for .308 and .223 3000-5k rds and I've never had a slam fire in my life.

I've had trigger malfunctions that produced a run away gun, and a couple catastrophic failures in 2015 and 2016 (Fuck you very much Freedom Munitions!) But never a slam fire.

 

[LRRPF52]

Same. Remington 7 1/2 as well.

I use Rem 7 1/2 the most because they are thick cup.

OP: Slam-fires aren’t “you’ll blow your face off” hyperbole. They are unintended accidental discharges due to a mechanical variable that the disciplined hand-loader can control.

Documented incidents of slam-fires in NRA High Power typically happened in the summer with muzzle-down orientation, which gave the BCG additional momentum to help the firing pin hit the primer harder.

Here’s a good description of it from Sierra. Reloading for Semi-Autos and Service Rifles

One thing that increases the likelihood of slam-fires is flush primer-seating instead of being recessed. Primers need to be seated .003-.006”, otherwise they are closer to the bolt face and allow more firing pin indentation/impact.

 

[LRRPF52]

Here is a chart to reference for those just getting into reloading for gas guns:

 

[308pirate]

I use Rem 7 1/2 the most because they are thick cup.

I used them because they gave me the best loads in my rifle. I never paid attention to cup thickness.

 

[FredHammer]

Here is a chart to reference for those just getting into reloading for gas guns:

I can't trust that chart after the glowing errors I immediately saw. Here is what I have measured:

WLR "B" .2095 "C" .125
WLRM "B" .2095 "C" .128
FED 215M "B" .2105 "C" .128

CCI #41 "B" .175 "C" .122
Ginex SRP "B" .175 "C" .120 (Non NATO)

 

[mtrmn]

I've had 1 slamfire in an AR15. CCI #400 SR primer. Gun was pointed downrange when I released the BCG sending a round into battery. 20 yrs ago or more.

 

[FredHammer]

Primers need to be seated .003-.006”, otherwise they are closer to the bolt face and allow more firing pin indentation/impact.

Word. I got a 21st Century Innovations hand primer and that thing is click per depth fucking awesome!

 

[vinniedelpino]

CCI 400s in 6.5CM SP brass will slamfire in one of my 6.5 man in ARs. It has an odinworks BCG.

It definitely can happen.

 

[TonyTheTiger]

It can happen. I'm all instances I've seen/read, it was also with an ultra light carrier and a steel firing pin. Titanium firing pins were all the rage in 3 gun

@TonyTheTiger might also have seen it happen. ROs see strange shit all the time

Yup. I've had one rifle and buddy had a rifle that after changing to a low mass BCG and buffer went into 2-4 shot burst mode fairly regularly. Both were fixed with titanium firing pins. Several different ammos tried, some handloaded with harder primers, some CCI 400's, some factory ammo. Backup triggers were swapped in in both cases with no change. Neither were gauged for firing pin protrusion or any diagnostics beyond "try a light FP and see what happens" were done.
Interestingly enough, of the dozen or so low mass system rifles I've got, this was only a problem in one, and it doesn't have the lightest components or highest bolt speed of the group.
I've seen plenty of instances while RO'ing of people having what I suspect is the same problem, hard to say when I never see the rifle again though.

 

[FredHammer]

Yup. I've had one rifle and buddy had a rifle that after changing to a low mass BCG and buffer went into 2-4 shot burst mode fairly regularly. Both were fixed with titanium firing pins. Several different ammos tried, some handloaded with harder primers, some CCI 400's, some factory ammo. Backup triggers were swapped in in both cases with no change. Neither were gauged for firing pin protrusion or any diagnostics beyond "try a light FP and see what happens" were done.
Interestingly enough, of the dozen or so low mass system rifles I've got, this was only a problem in one, and it doesn't have the lightest components or highest bolt speed of the group.
I've seen plenty of instances while RO'ing of people having what I suspect is the same problem, hard to say when I never see the rifle again though.

Here I was thinking about going low mass in the AR10 DPMS/Aero M5 style to reduce some overall rig weight...maybe now I shouldn't and just "Suck it up buttercup!" with the few extra ounces.

 

[msgriff]

LMT has an optional firing pin spring for their 308 BCG, which isn't required to function. I wonder if it's universal enough for other brands of BCGs. Might be worth a try for $3.50.

 

[FredHammer]

LMT has an optional firing pin spring for their 308 BCG, which isn't required to function. I wonder if it's universal enough for other brands of BCGs. Might be worth a try for $3.50.

Very interesting!

Wonder why the firing pins themselves aren't thicker on the circle part, yeah my nomenclature is fucked this morning, to prevent them from going too deep?

 

[TonyTheTiger]

Here I was thinking about going low mass in the AR10 DPMS/Aero M5 style to reduce some overall rig weight...maybe now I shouldn't and just "Suck it up buttercup!" with the few extra ounces.

Ehh, if I was just after weight loss I'd look towards static weight way before reciprocating parts that affect the function of the gun.

 

[FredHammer]

Ehh, if I was just after weight loss I'd look towards static weight way before reciprocating parts that affect the function of the gun.

Yeah, but I can't think of anything else other than that brick BCG.

 

[msgriff]

Yeah, but I can't think of anything else other than that brick BCG.

The difference between a LMOS and a FMOS is around 4 oz. (14 oz. vs 18 oz. for the JP BCG).

 

[roostercogburn98]

Didn’t mythbusters try to get some guns with floating pins to go off? I don’t think they did it, but that was a long time ago

 

[AMGtuned]

Didn’t mythbusters try to get some guns with floating pins to go off? I don’t think they did it, but that was a long time ago

I got shut down in a discussion here once. Regarding FA FCG's. But the similar thing applied in regards to slam fire/oob discharge.

I was GUARANTEED that due to the design, oob discharge was all but impossible.

I guess in this case, the bolt is in battery fully.

Not singling you out. Just reminds me of a time.....

 

[buffalowinter]

I've had a slam fire when grit got into the action and got the firing pin stuck in a forward position. Happened at a National Championship.

 

[srt-4_uk]

Didn’t mythbusters try to get some guns with floating pins to go off? I don’t think they did it, but that was a long time ago

I want to say their test was about vibration. Closed bolt but riding around in the back of a car.

 

[roostercogburn98]

I want to say their test was about vibration. Closed bolt but riding around in the back of a car.

Your probably correct on that. I thought I had seen an episode where something similar had been tested

 

[srt-4_uk]

Your probably correct on that. I thought I had seen an episode where something similar had been tested

It was riding around in a car with subs, not just car vibrations.

https://www.theakforum.net/threads/mythbusters-and-the-floating-firing-pin.82077/

 

[mewillis]

LMT has an optional firing pin spring for their 308 BCG, which isn't required to function. I wonder if it's universal enough for other brands of BCGs. Might be worth a try for $3.50.

Armalite AR10 FP spring is standard, has been for many years, not sure about KAC

 

[mtrmn]

Here I was thinking about going low mass in the AR10 DPMS/Aero M5 style to reduce some overall rig weight...maybe now I shouldn't and just "Suck it up buttercup!" with the few extra ounces.

Not worth giving up even more reliability in a large frame, IMO. It's hard enough to get them to function as it is.

 

[Jsp556]

Armalite AR10 FP spring is standard, has been for many years, not sure about KAC

You beat me to it.

 

[TonyTheTiger]

Forgot about another case of the slamfires that no one in here is likely to run into.
Go get yourself a French MAS-49 or 49/56. Shoots surplus ammo great. Then go get some modern ammo with modern primers, and the heavy floating firing pin will either need the tip shaved down or replaced by a lighter one, or you'll have an accidental kind of automatic rifle.

 

[45-90]

In researching SRP, I came across the old repeated warning about AR platforms needing thicker cupped primers to thwart the dreaded slam fire potentiality. Is there even one documented/verified instance of a slam fire happening in an AR because of the use of regular SRP?

I think about how many millions of .223 factory rounds (Not 5.56 NATO with thick/hard primers) have been fired through AR15s in the last 30yrs. Nobody ever says you can't shoot .223 ammo in an AR15. However, when the question directed at hand loading, it's "OMFG, better use those #41s or you'll blow your face off!" Also to consider is the service rifle competition shooters. They aren't all using #41 primers, are they?

Nope not me...don't know about all the rest of the guys.
I fired a thousand rds in one sitting, changing AR components to get it to fire 1085 rds per minute, with out hammer follow through. All rounds loaded on the Dillon with standard primers, Win 748, and all manner of used brass, much of it LC. Never had a slam fire, in many thousands of rds in various ARs in various calibers. I use 41, 7 1/2s & BR4s sometimes...but many thousands of 5.56 and 300 Blackout with standard primers. For me it ain't necessary, and I ain't gonna stop shootin if a primer is unavailable ...but for you, do what you feel is best.

 

[Bigfatcock]

Armalite AR10 FP spring is standard, has been for many years, not sure about KAC

Colt had them on the LE-901, AR-901, and CM762 rifles.

 

[45-90]

Here I was thinking about going low mass in the AR10 DPMS/Aero M5 style to reduce some overall rig weight...maybe now I shouldn't and just "Suck it up buttercup!" with the few extra ounces.

I have a 6 lb 3 oz AR 10 308 with no issues. It has a titanium bolt carrier, magnesium reciever, carbonfiber handguard, titanium muzzle brake, 16" fluted barrel, SA adjustable gas block, stand Areo lower with aftermarket 2.5 lb trigger. Accurate with the new 169 and 177 gr SMK, LC brass. Hundreds of rds fired... No slam fires, or 2 shot burst...yet.