AR Sponsor
Posted: 11/28/2013 5:14:55 PM EDT
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Hello new to the forum here,
I have owned AR rifles for quite a few years. I just puchased a dpms ap4 and got around 10 rounds through it. I sighted the rifle today ,but was making a few final adjustments when I had something scary happen and I immedieately stopped the sight it. I was loading one round at a time by dropping bullet into chamber with the mag out and firing that way. the first few rounds worked well ,but on the 3rd round when i released the bolt to slide forward (with bullet seated in chamber and weapon on safe) the gun fired.... Luckily it was pointed in a safe direction ,but I did this again with the mag in and the same thing happened. So I pulled the rifle apart to inspect I saw that everything looked normal on the bolt ect and that the lowers saftey mechanism was working properly. So I dropped a bullet into the chamber and noticed that the bullet wasnt seating properly the rim is about .1 from sitting flush to the rim. So I put the gun back together swapped ammo (from winchester to hornady match) did the same thing and it fired once again. naturally I'm going to take it back ,but was just wondering if this was common. Thanks, Any input appreciated |
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one thing to check is the firing pin.
it "floats" i.e. it's loose in the bolt. make sure its not stuck in the forward position,or broke, with the tip sticking out the front of the bolt. holdiing the bolt carrier assembly in your hand pull the bolt out as far as you can and the tip of the firing pin should not protrude,and should move freely. does it do this when firing from a magazine? i ask because i'm specifically warned not to single load a .458 Socom, letting the bolt slam forward on a already chambered round will allow the inertia in the firing pin to fire the round (a "slam fire"). but thats a .458 and not your .308 i've never had it happen in my LR308, but i've never sine loaded a round either. its a start,the other possibility is in the FCG (fire control group) and if you don't feel comfortable i.m SURE DPMS will fix it for you. call em and ask em , be careful |
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Quoted:
it has only happened with mag not in, its been stiff on unchambering a bullet since i got it. only reason i have kept mag out is due to trying to make it happen again. different ammos win, hornady match, and federal all have done it. I don't have 308 AR platform experience, but a 5.56 AR floating firing pin dents the primer of a bullet as it is loaded. Military primers are harder/thicker to prevent slam-firing. If you are using commercial 308 ammo instead of 7.62x51 ammo, the thinner 308 primers could explain what you are experiencing. Try some 7.62x51 ammo and see if it fires. The correct fix is to replace the firing pin with a lower-mass pin or one with spring damping (if they even exist). |
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Also is it normal for the cartrige not sit flush?
http://i268.photobucket.com/albums/jj10/dodgeram071500/IMG_20131128_164605_317.jpg http://i268.photobucket.com/albums/jj10/dodgeram071500/IMG_20131128_184548_645.jpg second pic is of gouging on bullet |
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I'm not experience with the DPMS 308 platform yet. But do load for both my M1 Garand and M1A, both civilian brass and also mil surp Lake city brass, all loaded for typical 308 and 30.06 loads on gas guns. I load the M1 30.06 with the same hard 34 primers also, and have had good luck with the CCI 200 on both rifles, both have a floating firing pin just like the AR system. You can get a slam fire, which is what I think you are getting, the normal round pickup off the magazine slows down the bolt during the typical reload so everything works fine, but I suspect that without the magazine and round sliding into the chamber, it's got to be a slam fire, so I wouldn't do that. If you had a stuck firing pin, happens, it would fire with your loading method, but would not chamber a round from the mag, because the case would jam into the firing pin as soon as it got high enough up the ramp. Most suggest not riding your bolt forward for normal loading but in this case if you must single load like this, then riding forward would be slower and probably won't slam fire. Just a thought. Think about how fast the bolt is slingshoting forward without the magazine in place. Oh and the rounds index on the front lip of the casing and chamber, not the primer end, your little mark on the bullets is probably the contact with the rifling in the BBL. The casing has to be sticking out like this so the extractor can grab it in normal operation, if it did seat all the way in the chamber, you couldn't extract it. I know it's old school, but having the extractor jump over the case lip when you load like this is not good, although lot's of people do it, it's not correct functioning of the load process, with a magazine the round slides up into the face of the bolt and slides into the extractor while the case is moving up the feed ramp. This is typical on all auto loading firearms. Plus there are lot's of rifles and handguns that have parts of the rear case not supported when chambered. Check out a 1911A1 with the case fully chambered, the rear bottom is hanging out in the air. Let us know what you have found out. No more slam fires ok, some ranges will have a problem with this ! |
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The LR-308 has a floating firing pin. Do not ever do what your were doing. It is to be loaded from the magazine only. The bolt stripping a round out of the mag reduces the bolt speed. Your lucky the rifle fired in battery or you would be wearing it. Its called a slam fire. Many a Garand and M-14 have been destroyed from the same practice. Next time you go out load one from the mag and then without firing it remove it from the chamber. You will see a nice little dimple in the primer where the firing pin hit when the bolt was released.
http://en.wikipedia.org/wiki/Slamfire |
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Quoted:
I'm not experience with the DPMS 308 platform yet. But do load for both my M1 Garand and M1A, both civilian brass and also mil surp Lake city brass, all loaded for typical 308 and 30.06 loads on gas guns. I load the M1 30.06 with the same hard 34 primers also, and have had good luck with the CCI 200 on both rifles, both have a floating firing pin just like the AR system. You can get a slam fire, which is what I think you are getting, the normal round pickup off the magazine slows down the bolt during the typical reload so everything works fine, but I suspect that without the magazine and round sliding into the chamber, it's got to be a slam fire, so I wouldn't do that. If you had a stuck firing pin, happens, it would fire with your loading method, but would not chamber a round from the mag, because the case would jam into the firing pin as soon as it got high enough up the ramp. Most suggest not riding your bolt forward for normal loading but in this case if you must single load like this, then riding forward would be slower and probably won't slam fire. Just a thought. Think about how fast the bolt is slingshoting forward without the magazine in place. Oh and the rounds index on the front lip of the casing and chamber, not the primer end, your little mark on the bullets is probably the contact with the rifling in the BBL. The casing has to be sticking out like this so the extractor can grab it in normal operation, if it did seat all the way in the chamber, you couldn't extract it. I know it's old school, but having the extractor jump over the case lip when you load like this is not good, although lot's of people do it, it's not correct functioning of the load process, with a magazine the round slides up into the face of the bolt and slides into the extractor while the case is moving up the feed ramp. This is typical on all auto loading firearms. Plus there are lot's of rifles and handguns that have parts of the rear case not supported when chambered. Check out a 1911A1 with the case fully chambered, the rear bottom is hanging out in the air. Let us know what you have found out. No more slam fires ok, some ranges will have a problem with this ! An ad can't let the round ride up the bolt face, the extractor is going to snap over the rim regardless of how its loaded. |
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The round needs to be "stripped" from the magazine. If you poke a round in the chamber, it doesn't do you any good to have an empty magazine in it at that point. Dropping the bolt on the already chambered round is not good regardless of whether there is a magazine in the gun or not.
Tony |
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Slam fire with soft commercial primers. Mil-spec primers are harder.
I've got a .45 DI AR that will do it about half the time if I drop the bolt on a chambered round, because pistol primers are usually softer than rifle primers. 1. Don't insert the round into the chamber fully before dropping the bolt. I sometimes single-load by just laying the round on an empty magazine through the port. 2. With nothing to slow the bolt, such as stripping a round or dragging on the follower, the bolt speed on closing will be higher, and therefore more likely to slam fire with the floating firing pin. 3. The case head will never be flush with the breech of the barrel. Fully seated, it should protrude about 3/16" from the breech. This is the depth of the case head pocket in the bolt. 4. If it were a stuck firing pin, you probably would have blown the bolt up already because it would have fired out of battery, so my money on it NOT being a stuck firing pin. |
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Just a minor modification for you. No more loading unless FROM the magazine. Quoted:
Quoted:
thanks guys this really helped no more loading without mag for me Just a minor modification for you. No more loading unless FROM the magazine. I single load with a mag in all the time when going for 500+yd, but I'm using once fired with mil primers and using the empty mag like a sled. It does make a small but noticeable difference in groups. |
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I found it funny when I saw your post as this same thing just happened to me while deer hunting. This was my first AR ND in 40 yrs. After it happened I remembered my squad leader warning all of us not to do this as a slam fire will be the result. We were instructed to load from a mag with the muzzle pointed up to be sure this did not happen. I learned this in 1969 so it is a know issue. There is nothing wrong with your rifle. Most AR's have floating firing pins and are capable of slam fires because of this. The armalite AR10 has a spring on the firing pin to help alleviate this common problem. You were unaware, I on the other hand should have know better.
Semper Fi |
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Quoted:
I know it's old school, but having the extractor jump over the case lip when you load like this is not good, although lot's of people do it, it's not correct functioning of the load process, with a magazine the round slides up into the face of the bolt and slides into the extractor while the case is moving up the feed ramp. This is typical on all auto loading firearms. 
Every AR-style rifle I've seen has had the extractor "jump over the case lip" on loading - even when stripping a round from the magazine. Take a look at the bolt face and the location of the extractor and you'll see there is simply no way for a round to "slide into the extractor." |
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Quoted:
Every AR-style rifle I've seen has had the extractor "jump over the case lip" on loading - even when stripping a round from the magazine. Take a look at the bolt face and the location of the extractor and you'll see there is simply no way for a round to "slide into the extractor." Quoted:
Quoted:
I know it's old school, but having the extractor jump over the case lip when you load like this is not good, although lot's of people do it, it's not correct functioning of the load process, with a magazine the round slides up into the face of the bolt and slides into the extractor while the case is moving up the feed ramp. This is typical on all auto loading firearms.
Every AR-style rifle I've seen has had the extractor "jump over the case lip" on loading - even when stripping a round from the magazine. Take a look at the bolt face and the location of the extractor and you'll see there is simply no way for a round to "slide into the extractor." If you take "all auto-loading firearms" to mean "except everything that doesn't have a rotating bolt" 
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