My M305 went kaboom

Status
Not open for further replies.
I am curious about something here:
You wrote that you dry cycled live ammo to test for proper cycling and check for no accidental firing. This is fine and most likely, if you looked at the primer on those cycled and still live shells they were showing a small dimple or indent on primer surface caused by slight contact by floating fire pin.

Is there a small chance that one of these shells was loaded in mag again and caused that accident at the range.

Commercial ammo primers do not have the same cup hardness as for the Milsurp ammo or CCI #34 primers.

BB




beavis_m305 said:
Yeah I'm aware of the floating firing pin thing. I cycled them out on the farm
Click to expand...
 
Some good pictures of your bolt's locking lugs would be nice.

I suspect that you may have a issue of excessive firing pin tip protrusion and a possible issue of firing pin tail/receiver retraction bridge issue, I.E. tolerance stacking.

You may also have a issue with too little headspace, I have seen several older, US imported, Chinese M14's come through that would not come close to closing on a Forster .308 SAMMI GO gauge.

I rarely see it mentioned out here, but firing pin tip protrusion is as critical of a dimension on M14/M1 Garand/M1Carbine rifles as headspace is.

Always make sure that your firing pin tip protrusion from the bolt face is near the minimum specs (not maximum specs) on these weapons, and that your receivers retraction bridge aggressively retracts the firing pin until the bolt has achieved about 50% closure. USGI ammo had hard primers that help to mitigate issues with firing pin tip protrusion, civilian and some NATO spec or foriegn made ammo may have much softer primers.

I am surprised that this happened with American Eagle ammo, I have had good luck with that ammo in the past.
 
Boom-Boom said:
I am curious about something here:
You wrote that you dry cycled live ammo to test for proper cycling and check for no accidental firing. This is fine and most likely, if you looked at the primer on those cycled and still live shells they were showing a small dimple or indent on primer surface caused by slight contact by floating fire pin.

Is there a small chance that one of these shells was loaded in mag again and caused that accident at the range.

Commercial ammo primers do not have the same cup hardness as for the Milsurp ammo or CCI #34 primers.

BB
Click to expand...

^^ Good point made
 
Zokakoka said:
^^ Good point made
Click to expand...

Beavis I'm glad you weren't seriously injured, that big chunk of forged steel between your face and the cartridge i'm sure helped.

After the pierced primer I experienced on S&B 150FMJs on firing(hard stikes for hard primers I assume), and now this episode I will definately use mil-spec primer cups.

Your episode is probaly firing pin related, because the "Slam Fire warning" in the Owners Manual( who reads these things anyway) should occur "in Battery" and on soft commercial .308WIN primers meant to operate reliabily on limp strikers like my Browning Lever Rifle 81.

I've seen enough from my own short experience with the M-14S, and other's, to treat these Rifles with the caution and respect they deserve. I want Military Pattern Rifles, and I have to understand what this employs when using Commercial .308. These are not sporting BARs or Remington 7400s. that you can push a .308WIN into the chamber and slam the bolt on it all day! I've owned enough of these to know that.:canadaFlag:
 
Glad that your ok. My 305 went boom a while back, bolt broke, mag blew out.

I managed to get the bolt replaced, don't use it much these days.
 
looks like a over pressure due to your gas system blowing off "was the bore clear"

Headspace or slam fire should not cause your gas system to blow off your gun
 
If the rifle fired as the operating rod was still traveling forward (ie: hammer hooks still held by the disconnector...trigger NOT pulled) then it eliminates all of potential causes relating to the trigger group.

As others have mentioned, the design of the rifle incorporates a floating firing pin, so I would want to make sure that the shooter did not pop one in the pipe, load the other two rounds into the mag, then depress the loaded rounds/follower and let the op rod fly. Without the resistance of stripping the a round from the magazine it is well within the realm of possibility that the firing pin can develop enough inertia to set off a primer before the bolt is completely closed...especially if the rifle has tight headspace.

Another potential failure mechanism would be if the shooter stripped the round from the magazine with the bolt, but gently guided the operating rod/bolt/bullet into the chamber. In this instance it is possible the operating rod would not travel all the way forward and consequently bolt lugs would not engage completely, however detonation of the round would only then happen when the trigger was pulled.

If the round was loaded correctly (ie: stripped from the magazine by a freely traveling operating rod moving entirely under the force generated by the op rod spring) and detonated without the trigger being pulled, then there is no doubt that what happened was an out of battery detonation. If the gun was in battery then the bolt would have held....the galling marks illustrated in the photograph support this statement as they indicate to me that the round went off before the bolt was completely rotated into their fully closed positions.

The most likely cause for this is not excessive firing pin protrusion (although pierced primers on other pieces of brass that were successfully fired would be a positive indication of excessive pin protrusion), rather the firing pin getting jammed in the forward position. All that cosmoline they drench the rifles with when shipping from the factory would be the first most likely suspect, and grease/oil put their by a well intended shooter would be the second. While the rifle is supposed to have features that physically retract the firing pin and only allow it to travel forwards when the bolt is completely in battery, I've seen many M305/M14S rifles where this feature was not functional due to some combination of a chipped firing pin tang and improper firing pin bridge dimensions in the receiver. Add to the sticky cosmoline (or owner induced "lube") a bunch of brass shavings that might accumulate within the firing pin channel you have a recipe for pinching the pin in the forwards position. If this happens, as the round comes tight in the chamber but before the bolt is finished rotating the protruding pin can crush the primer. As the bolt is not completely in position, the lugs are unable to take the pressure developed by the round and things vent backwards.

I would want to know more about the tight headspace of the rifle (ie: was it tight by chinese specifications which could still land it over .308 nato spec...this would increase the safety factor...or was it really, really tight...ie: the 0.002 crush special (1.628"...0.002" under .308 SAMMI Go ) that some folks look for, and at their peril I will add). This could have some bearing however based on what's been described about the circumstances surrounding the failure so far I would be looking for a reason the firing pin could get pinched forwards.

Good luck with your gun....and for others reading make sure you understand how your M14 type rifle operates. There are several different ways this can happen and my observation is that it is happening more and more frequently. I love the M14 platform and continue to shoot many thousands of rounds a year through the couple I keep...but the rifle definitely has some peculiarities that owners/shooters should be aware of.

Cheers,

Brobee
 
pinkfloyd said:
I see red goo in yuor locking lug pic. What are you using for grease? try lubriplate,(white lithium grease.) May have gumed up your firing pin like someone said earlier. Call Hungry or m14 Doctor. good luck
Click to expand...


That red goo is wheel bearing grease, i use the same stuff to lube up my m14s, have never had problems with any of my 6 M305's because of it .. im leaning on ammo for this one.
 
Last edited:
drache said:
Headspacing problem that caused the slamfire?

*Dont mind me I've been up for 36 hours straight and so Im tired and guessing :p*
Click to expand...

Apparently so :feedTroll: slam fires occur when reloaded ammunition has a high primer as well as the design of the the firearm does not lend itself well to stuck or hungup firing pin
 
Wow, thanks for the replies gentlemen. I'll try to answer all your questions as best I can.

Fenix is correct - the lube I use is Nulon chassis grease

The slam fire occured when I let the bolt go from locked back position, to strip a round off which was seated in the mag.

The rounds I cycled through the gun to test function were not fired or loaded at the shooting range - I still have them.

I have inspected the bolt - it's body, lugs, etc and to the eye it seems like it survived undamaged. I can't see any distortions or cracks. Firing pin is ok.

The barrel was clear. RE: the gas system "blowing off" - it didn't go flying down the barrel. After this event it was loose. Upon undoing the gas lock, I could grab the gas cylinder assembly and pull it clear of the stock ferrule I believe it's called? The metal tab on the barrel that the lip of the stock clips into. I couldn't do that before to save my life, it was on there snug. Is the gas cylinder meant to be on tight or free moving onces the gas lock is undone? The hand guard popped off too. What would cause that?

When i got it I squirted the #### out of the bolt assembly with Brake clean until nothing brown was coming out - in other words it was clean and dry and this is the way I left it.

I don't know if it means anything to you guys RE the head space of my rifle, but a guy over here measured 6 prvi partisan cases i fired out of my rifle with the gas system turned off. He found that my case lengths after firing were 93.08 to 93.10mm with the median being 93.10. So my cases were stretching 0.51mm. His conclusion was that my headspace is slightly tighter than the other two rifles tested, but not by much. The other two rifles fired cases were measuring 93.12mm on average. But that doesn't take into account different brass manufacturers etc

If it means anything, one of the cases I recovered had a badly flattened primer that looked like it backed out a little too. I looked through a packet of fired Prvi Partizan cases and the primers on them looked fine.

So it appears the fault may have lied in the firing pin some how... it still makes me wonder if the primer on that round was protruding a bit.

I will probably end up sending it to a gunsmith over here thats an expert on military style auto loaders, just to see if it's safe. I managed to salvage the magazine too :) Thanks again for the replies, hope my replies are helpful too. But I am an M14 noob, I never realized there was so much to these.
 
is there bolt replacement that could have avoided this problem ?

I now that for the sks, they made a spring to add to the firring pin to make it non-floating, anything like that for the m14 ? (to avoid punching the primer on bolt closing ) ?
 
beavis_m305 said:
I don't know if it means anything to you guys RE the head space of my rifle, but a guy over here measured 6 prvi partisan cases i fired out of my rifle with the gas system turned off. He found that my case lengths after firing were 93.08 to 93.10mm with the median being 93.10. So my cases were stretching 0.51mm. His conclusion was that my headspace is slightly tighter than the other two rifles tested, but not by much. The other two rifles fired cases were measuring 93.12mm on average. But that doesn't take into account different brass manufacturers etc
Click to expand...

Case length is nominally 51mm.
I have no idea what these measurements of 93.08, 93.10, etc. are about. Headspace dimension will be measured from the casehead to a point on the shoulder.
 
Status
Not open for further replies.
Back
Top Bottom