March 13, 2011, 02:37 PM | #1 |
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My FN-49 Blew Up!
Well, sort of. I was at the range Friday and I experienced what I think was an out-of-battery ignition. I was shooting my AL FN-49 with Winchester 150grn Power Point JSP (factory ammo, not reloads) and on the third or fourth shot (I wasn't really counting) I noticed that it was much louder and that I felt some powder residue hit me in the face. I immediately locked the bolt open and removed the magazine in order to get the rest of the unfired cartridges out. It was then that I noticed that the bolt would not go foreward because of a shard of brass blocking it, the stock was cracked in front of the magazine, and the reciever cover retainer and sliding dust cover were bent outward. I managed to remove the shard of brass and get the bolt closed, but needless to say I was done shooting that particular gun for tha day.
I later managed to find most of the culprit shell casing which was mangled beyond belief. When I got home, I took the rifle apart and repaired the crack in the stock and bent the reciever cover retainer back into shape (the dust cover fell off when I was inspecting it, but it was already bent and really needed to be replaced anyway). I also disassembled the bolt (I'd already replaced the one-piece firing pin with the later two-piece design) and inspected the trigger, sear, hammer, and auxillary sear and I couldn't find any obvious reason for the accident. Yesterday, I took the rifle and the magnled casing to the gunsmith at my local Gander Mountain. He seemed to be fairly familiar with FN-49's as his first question was about whether or not I had the one-piece or two-piece firing pin. He inspected the rifle and told me that it was mechanically fine and that the only two reasons he could think of for the mishap were either debris stuck in the firing pin channel or a defective round of ammunition. I very highly doubt that debris in the firing pin channel was the cause because the rifle had only fired two or three shots before the incident and was cleaned prior to that (I always clean my guns every time I fire them) and the only lube I'd ever used on this particular gun has been a very light coating of oil (usually Remoil). Also, the firing pin was not protruding immediately after the incident, when I disassembled the rifle at home, or when the gunsmith inspected it. This leads me to believe that the ammo was probably the culprit and I plan to send an e-mail to Winchester about the incident. Honestly, I think it's probably a testament to the design of the rifle that I was not injured and that the gun wasn't damaged any worse than it was. Even so, I'm probably going to sell this rifle now (though at least I can do it with a clear conscience given the gunsmith OK) as it scared me pretty badly. As I was researching the problem Friday night, I read on a couple of forums that FN-49's are somewhat known for slamfires and OOB ignitions and that they can be kind of sensitive about commercial ammo's softer primers. Since I don't reload 30-06 and milsurp ammo is getting scarce, I really have little use for a rifle in that caliber that I can't shoot commercial ammo in. Also, I find myself somewhat questioning the need for a semi-auto in a full-caliber cartridge (particularly when my K-31 is so slick). |
March 13, 2011, 04:17 PM | #2 |
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First and foremost, I'm glad you nor any bystander was hurt.
Second, you mind posting some pics? I'd like to see what the hubbub was all about...
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March 13, 2011, 04:45 PM | #3 |
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I'll see if I can't borrow a digital camera to snap some decent pics with. Honestly, other than a missing dust cover it's difficult to tell that anything happened to the rifle as the cracked stock was the worst damage and I've already repaired it. The spent casing, on the other hand, is another story. The case head is nearly separated and the rest of the case looks like someone rung it out like a wet dish towel. I really feel fortunate that I didn't have to pick anything out of my face and I'm suprised that I didn't have to clean out my trousers afterward.
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March 13, 2011, 06:36 PM | #4 | ||
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Yes, please provide pictures.
I have handled FN 49’s, I assume that it has the same free floating firing pin arrangement that FAL’s have. Quote:
From the answer you got from the Gander Mountain man “its all your fault”, it sure sounds like he is one of those old school acolytes. You will see this sort of thinking in old legacy posts from Bart Bobbitt. The link is in this thread http://thefiringline.com/forums/show...9&postcount=40 And my reply was here http://thefiringline.com/forums/show...4&postcount=41 Even though Bart actually witnessed slamfires, he could not and would not acknowledge that primer sensitivity was the cause. His convoluted explanation of the evidence before him is all based on the group think of the era: that only high primers or defective guns have slamfires. Until that generation is below the ground, and silent for decades, you will continue to hear the same wrong answer. Winchester redesigned their primers around 1999 to make them more sensitive. I called and was told “this was to combat off center firing pin hits.”. I will bet that your firing pin is especially heavy. I am going to assume that FN49’s and FAL’s have similar free floating firing pins. I am aware of a Gun Club bud who loaded ammunition with brass finish WLR and the gun slamfired, in battery thank goodness, when he put a round in the chamber and dropped the bolt. This is how the military manual told him to load the thing single shot. The slamfire so un nerved him, he left for home and did not fire another round. He told me he disassembled the mechanism, everything was as clean as the night before, and there were no broken parts. There are reports from the web with slamfires in FAL’s. It is obvious that given a sensitive primer, FAL’s will slamfire. If you are unlucky, it will slamfire out of battery. I would recommend never using Winchester ammo again and to roll your own. I recommend the use of “mil spec” primers, which are less sensitive than the commercial brands. CCI#34’s are advertized as mil spec, I have read that some Russian primers are harder than rocks. That is just great. Less sensitive is better than more sensitive in these military rifles. I will recommend small base sizing, use a case gage and size to gage minimum, seat all primers by hand to ensure that all are below the case head. Quote:
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March 13, 2011, 08:36 PM | #5 | |
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Quote:
I've had issues with this rifle slam-firing before but thought I had fixed them. Before, the gun would intermittently fire 2-3 rounds with a single pull of the trigger, but never out-of-battery. I replaced the older one-piece firing pin with a newer two-piece one and replaced the firing pin return spring with an extra-heavy one. This seemed to fix the issue when I used Federal Power-Shok ammo (the type I normally use in this rifle because I usually find it the cheapest). The incident in question was the first time that I'd used Winchester ammo in several years (I did run a box through the gun not long after I bought it but had feeding issues at the time). The Gander Mountain gunsmith didn't really insinuate that the incident was my fault as he did concede that the ammo may be the issue. His thought was that perhaps some bit of material got into the primer pocket under the primer during the manufacture of the ammo and that may have caused the round to fire before the bolt was fully in battery. The only other situation that I can think of is that perhaps my gas system should have been readjusted for the Winchester ammo. As I mentioned earlier, I normally shoot Federal ammo in this rifle and thus had last adjusted the gas system for that. I suppose it is possible that the Winchester ammo may have been hotter and thus caused the action to open before the pressure had dropped sufficiently. I find this unlikely, however, because from what I've read, such a problem usually results in the case sticking in the chamber and the bolt either failing to cycle or ripping the rim off of the case. |
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March 13, 2011, 09:08 PM | #6 |
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Pics
As promised, here are some pics of the culprit case (or at least most of it).
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March 13, 2011, 09:47 PM | #7 |
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That's just one, mangled mess. Not that you needed me to state the obvious...
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March 14, 2011, 06:18 AM | #8 | |
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Quote:
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March 14, 2011, 08:09 AM | #9 |
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Not sure why you said your rifle blew up, unless it was just to get everyone's attention.
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March 14, 2011, 10:56 AM | #10 |
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My memory of the FN-49 is a little hazy, but doesn't the bottom curve of the bolt carrier & the tunnel for the firing pin in the bolt carrier prevent a following hammer from contacting the firing pin till it is 99% in battery?
In the FAL, which is a development from the 49, the hammer may follow through, but can't contact the firing pin rear till the bolt has dropped into the locking recess & the carrier moved forward exposing the firing pin. If I had to guess I'd say high, or defective primer, or jammed pin in the forward position.
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March 14, 2011, 01:57 PM | #11 |
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I have never fired an FN-49, I know Garand shooters all caution against using hunting ammo in the M-1. Try some milsurp FMJ, see if that makes a difference.
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March 14, 2011, 04:55 PM | #12 |
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Strange,one of the gentlemen on surplusriflerorum.com had a similar incident,only his FN49 was an Argentine 308,but it too I believe was Wichester ammunition,white box ,the case imploded similarly to what you have shown in your pictures.
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March 14, 2011, 05:57 PM | #13 |
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Well, first it is NOT a sensitive primer going off from the bolt hitting it. The primer shows a clear firing pin mark. Nor do I think it is a result of firing pn creep, where the inertia of the firing pin causes it to impact the primer. When that happens the primer is usually flattened back out since there is no resistance to the firing pin being forced backward.
The firing pin mark is too clear for that and very obviously the result of a full hammer impact on the firing pin. (That type of firing pin "crater" requires a certain firing pin support and the primer clearly shows that support.) Further, the firing pin mark is centered, meaning that the cartridge was fully into the bolt face and under the extractor so the bolt had to be around 1" or less from complete closure. I think that at one point, the bolt or the carrier stopped its forward motion, short of battery, for some reason. The shooter, not realizing the bolt was not fully closed, pulled the trigger. (That gun does not have a disconnector.) Some defect of the gun allowed the hammer to reach the firing pin; the extractor held the case head firmly enough to ensure good support for the case and permit a full firing pin blow. And ka-boom! The case seems to confirm the above theorizing. The case blew out, but enough was in the chamber that high pressure gas came back around the case, crushing it. The internal pressure meanwhile had blown the head off the case in the classic "excess headspace" condition. There was probably enough pressure to push the bullet out the barrel; the OP doesn't say, but I think he would have mentioned a stuck bullet. There you have MHO. Jim |
March 14, 2011, 07:52 PM | #14 |
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I agree about the firing pin impression, what bugs me is the line from the impression over to the edge of the primer!
That looks like the pin was pressed into the primer when the bolt unlocked (or locked) I can't tell which, but I'm favoring locked because of the center hit on the primer cup. If that's the case we're looking at a gas system malfunction not having enough dwell time before unlocking, or a shot locking shoulder or bolt locking face.
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March 14, 2011, 09:11 PM | #15 |
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I don't think there is premature unlocking, as that is about impossible in a gas gun where the bullet has to reach the gas port to start the unlocking process. I don't think the gun was ever locked, and that somehow the hammer reached the firing pin with the bolt partly open.
I see what you mean about the line, though. It looks like what you might see in a dropping barrel pistol, but the FN-49 bolt doesn't drop at the front. The only way I can see that line happening at the time of firing is if the bolt was actually blown upward or to the side, leaving that mark as the firing pin scraped the cartridge case. What happened to the bolt and bolt carrier? Did they blow out of the gun? Also can you tell where the extractor was? Those look like extractor scrape marks on the (viewer's) right side of the picture. The extractor position would let us orient the case the way it was in the gun. A thought, though. One thing that could stop the bolt carrier and the bolt would be the gas piston if it stuck out part way. Can you check to see if it might be bent or have a burr or something that could do that? Jim |
March 15, 2011, 08:57 AM | #16 |
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You may be right about the extractor, either there or it caused the chunk ripped from the rim a t 6 o'clock? Hard to tell looking at just a fuzzy pic. Is the extractor in a FN-49 in the same orientation as in a FAL?
The only reason I mentioned premature unlocking is that there was an incident a while back with a FAL (as close as I can claim to expertise with an FN-49) where there was a slightly over-length gas piston fitted. There is meant to be a small (1/8" or so) gap between the piston rear face & the bolt carrier front face. this is designed (in a FAL) to create a short delay before contacting the bolt & carrier so that the breech pressure can drop lower before starting the unlocking camming. What that shooter was experiencing was very similar & it took a while to figure out as the difference was so slight it needed measuring to even find it.
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March 15, 2011, 02:07 PM | #17 |
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Good point, wogpotter, and I also thought of a gas port setting too tight, but the problem is that those things would cause a problem on every shot, not the third or fourth. I would like to see that rifle and see if there is a point where the hammer can reach the firing pin with the bolt out of battery. I have been trying it with my 49 and can't get it to do anything wrong, but it does look like some wear might allow contact.
Something like a wrong or incorrectly made (repro?) part cannot really be ruled out after so many years and many hands. I hate it when something like this happens and the quick glib response is "Oh, they fire out of battery all the time" or something like that. "They" shouldn't, and I like to find out what went wrong, not just talk about floating firing pins that don't float or high primers that aren't high or reloads that aren't reloads. Jim |
March 15, 2011, 03:58 PM | #18 |
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I know what you mean.
I replaced the 1-piece firing pin in my FAL as they have similar pin breakage issues. After swapping them I had too much FP protrusion with "identically interchangeable" parts! I ended up using a FP protrusion gauge & re-grinding the FP front half's tip, but only after a lot of checking to find where EXACTLY the discrepancy was. Luckily I discovered the problem before there was a problem.
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March 15, 2011, 06:26 PM | #19 | |
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Quote:
I had two out of battery slamfires in Garands, the second blew the receiver heel into my face. Both cases had nice deep firing pin marks. No primer cupping either. I had one inbattery slamfire with a AR with the new brass finish WSR. The primer mark was indistinguishable from any other round I fired that day, no primer cupping. And the second shooter on my firing point, he had a AR slamfire, with Federal match, and his primer looked like any fired primer. Nice deep primer mark. no primer cupping. In a recent Rifle or Handloader magazine, Mike Venturino shows the back end of a 7.62 Russian slamfire case. Not a shallow primer mark, though on his rifle, there is some cupping. I don't know why this is so, but it is so. Maybe someone can install a high speed camera in the bolt face and figure out the mystery.
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March 15, 2011, 08:48 PM | #20 | ||||||
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Originally posted by Jim Keenan
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Originally posted by wogpotter Quote:
Originally posted by Jim Keenan Quote:
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Originally posted by wogpotter Quote:
Also, I considered maybe a problem with the sear or auxillary sear engagements allowing the hammer to follow. However, none of those engagements appear worn nor was I able to make the hammer follow in messing with it unloaded at home. In order for the bolt to travel rearward enough to feed a new cartridge, it always seems to ride back far enough to re-cock the hammer no matter how I try to manipulate the rifle. |
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March 15, 2011, 08:54 PM | #21 |
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Well, Slamfire, I guess I have to bow to expertise as you have had and seen more slamfires than anyone else I have ever known.* But in my much more limited experience, a slamfire with no backup to the firing pin (that is nothing but firing pin inertia) will let the primer internal pressure push the primer metal back out, even into the firing pin hole if the design allows it. It takes a goodly amount of firing pin inertia and case support to get that kind of primer appearance.
The high primer type slamfire is the result of the bolt face hitting the primer; there usually is no firing pin mark at all since the firing pin didn't set off the primer, the bolt face did. The FN-49 and FAL both have very strong firing pin springs just to prevent firing pin creep and possible slam fires, since the bolt is moving straight forward and no inertia is taken up by the bolt turning. I still think there is something about that KB we don't know. *Nine times out of ten when someone says "slamfire" they mean the bolt was locked but the sear jarred off or a light trigger was pulled accidentally, but that certainly is not the situation when a receiver blows apart. Jim |
March 16, 2011, 08:04 AM | #22 |
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Bear in mind we're just guessing here having not had the actual rifle in our hands. Also bear in mind no-one is "having a go" at you, we're just curious to find a definite answer to what & how this happened.
2 things that come to light from your post. Firstly that is an abnormally high incidence of incidents. Secondly there was a change made (the spring). Based on that I'd guess there is a problem somewhere within the rifle/ammunition/user chain. I don't think it is drastic, but it IS causing incidents so it probably needs fixing for your comfort & safety. Ammo with 10 FPS is very, very minor, but ammo with a different pressure curve from a different propellant may well be causing the gas to behave differently, even if the velocities are identical.
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March 16, 2011, 09:42 AM | #23 | |||
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Either way, I'm getting rid of this rifle. Even if it is mechanically fine, I have no use for a gun that I have to be so picky about ammunition with. I feel that I can sell it in good concience since a gunsmith has given it the mechanical OK. I've also opened the gas vent all the way (this allows the least amount of gas to act against the piston) and set the plug to the grenade launching setting (this prevents semi-auto fire) so that whoever I sell it to will have to adjust the gas system for whatever ammo he decides to use. |
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March 16, 2011, 08:07 PM | #24 |
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You had more slamfires before? What happened those times and how often have you rebuilt that rifle? There has to be something wrong somewhere.
That is a bit like someone saying he is getting tired of being struck by lightning! Jim |
March 16, 2011, 08:17 PM | #25 |
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I sure hope you plan on telling the next owner about your experience with this rifle.
And, one gunsmith, who may or may not have been familiar with the rifle, wouldn't ease my conscience if the next owner got hurt because the problem re-occurred. I know its a bite in the butt, but, I don't think my conscience could rest very easily after I sold the rifle for anything other than a wall hanger, making dang sure it was disabled from every firing another round again. And, frankly, I am surprised the Gander Mt. Gunsmith gave you a go ahead to re use the rifle, did you get it in writing? Cause if somebody gets sued, you better have either a no fire letter signed by the buyer, or paperwork covering your butt. I myself, would torch the dang thing, eat the lost money, and sleep better at night. |
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