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Posted: 8/4/2003 1:22:24 PM EDT
While shooting a new Bushmaster (.223) the firing pin came loose because it had bent the retaining pin and got past it. I was shooting Russian 62 gn ammo (steel case Barnaul, FMJBT) and someone told me that was the problem. I've been through many rounds of this ammo before with another AR with no problems. The Bushmaster firing pin is one of their titanium types. I'm thinking the lighter firing pin is getting slammed too hard by what appears to be hotter ammo. Any ideas ..... thanks!
Link Posted: 8/4/2003 7:15:56 PM EDT
[Last Edit: 8/4/2003 7:20:56 PM EDT by fight4yourrights]
Russian 62 gn - not my 1st choice in ammo. Not even my last choice. I don't shoot russian, but that's not your problem. Titanium firing pin - a solution looking for a problem that causes more problems. Replace that Ti pin with a standard pin, sell it to some sucker on Ebay. It buys you nothing, MAY have caused this problem, and they are known for having the tip chip and pierce primers, sometimes with bad results. Let me ask - WHY did you feel the need to replace the standard firing pin with a Ti pin? You buy cheap ammo, and expensive firing pins.
Link Posted: 8/4/2003 7:23:55 PM EDT
Nope. I've shot thousand of rounds of ammo though my half dozen (or more [:)]) AR's - some of it Barnaul, Wolf, and S&B and other God forsaken cheap ammo but I can see nothing sort of a case seperation is going to drive that tiny firing pin back hard enough with the short stroke available to push the firing pin retaining pin out of the way! The things stick out a few thousandths of an inch from the bolt face - pressing into the "soft" primer seal to cause them to pop. The maximum travel of the pin within the bolt is only about a quarter inch from hammer strike to primer impact. To bend a retaining pin that thick with such a short stroke the energies must be huge. Looking at it I can't figure out a way to hit or pull the firing pin hard enough to bend that relatively large retaining pin. I [i]only[/i] quality as expert on the military range so I don't need a Ti firing pin - possibly the shape of the lip is wrong? Looking at my pins I see no wear where the pin is slamming into the retaining pin (which is blued and might show hard impacts). The stock USGI pins are a gently rounded 90 degree lip there - the entire movement range is barely the thickness of the ring there. My idea/suggestion would be to restore your weapon to USGI spec's replacing the Ti pin with a stock one. When you reach the President's 100 you can put the Ti pin back in to increase your lock time [:)] Damn, now I got CLP all over me and the keyboard ... [;)] the way I like it.
Link Posted: 8/5/2003 7:56:03 AM EDT
Paul and fight4yourrights, thanks for the replies guys. I think you're both right that I should replace the Ti pin with the stock one. I just put it in there because I like hi-tech kind of stuff and thought I'd try a titanium pin. I only encountered the problem the one time so maybe it was a round that was double charged or something like that. To answer the question about cheap ammo, I've used Russian, Greek (Olympia), IMI, Remington and many others with never a problem with any of them. In any case, I've just changed the firing back to stock. Again, thanks for the great replies. NRA4EVER! [%(]
Link Posted: 8/5/2003 8:26:57 PM EDT
I really don't think it's being caused by the titanium firing pin. Although I agree that they are a problem to a solution that doesn't exist. I work with an officer from another agency who has a leo Rock River carbine. Everything is box stock RR. He goes through firing pin retaining pins like they are going out of style. He only shoots Winchester Ranger law enforcement ammo (55 gr)through his carbine. I shoot the same ammo, just a different bullet weight (64 gr). I don't have the problem in my Colt M4, that he has. Both guns are high mileage weapons. I cannot for the life of me understand why this is happening. I know another officer who has the same problem with his carbine, but I can't remember what brand that it is. If someone has an idea, I would sure like to hear about it. Thanks!
Link Posted: 8/6/2003 2:03:59 PM EDT
[Last Edit: 8/6/2003 2:47:33 PM EDT by JohnM]
A firing pin retainer can be bent by several actions of the weapon and or parts not working in coincedence. One is you can have an M16 firing pin (has a larger collar than an semi) and this catch's on the hammer lip (providing your hammer has that upper rear section milled, then there is a small shelf with a squared off lip). Second is your disconnector does not retain the hammer low enough or not at all during a portion of the action cycling. Again, this lip impacting the FP itself. The geometry of the action cycling can be tested manualy and you can determine indeed where the problem lays.
Link Posted: 8/7/2003 7:14:05 AM EDT
JohnM, Thanks for the reply. I had forgot to mention that I had installed a JP Fire Control system, hammer and trigger; it seems all is adjusted exactly right with a nice 3 1/2 pound trigger, very little creep, and very little overtravel; however, now that I've looked at it again, after reading your reply, I can definitely see how the hammer may not be held down enough by the disconnector on the return part of the cycle. This bending of the retaining pin only happened once and the rifle shoot without incident the rest of the morning, so I guess I will keep things as they are to see if it happens again. If it does, would you suggest removing a little of the upper corner of the hammer? I don't think this would bother the contact with the firing pin; the only other thing I can think of is to add material in the grove of the hammer where the disconnector holds it. I would rather not disturb the trigger system as it is just as I wanted it, and I put the screws down with 'red' loctite, as suggested by JP. - [%(]
Link Posted: 8/9/2003 6:52:55 PM EDT
Rickoshay, If you pull the bolt to the rear and slowly allow it to go forward can you feel the bolt drag as it rides over the hammer?
Link Posted: 8/10/2003 9:11:34 AM EDT
Tweak, no, I don't feel any noticeable resistance that I would attribute to the hammer rubbing the firing pin or something like that. In fact, I have tried to get the hammer to touch the firing pin by taking the bolt out of the upper carrier and placing it on the lower and manually cycle it back and forth over the hammer. It looks like it gets mighty close, but I think they're all like that. In any case, I have even tried putting a little downward pressure on the end of the firing pin from the top of the bolt as I slide it forward over the hammer and can't feel the hammer touch the firing pin. I do think JohnM is right that this would be a good way to bend the retaining pin and I'm now convinced that that is what happened. These retaining pins are fairly heavy duty steel and it would require a lot of force to bend one enough to let the firing pin go past it like mine did. By the way, there is absolutely no up, down, or sideways play at the oversize JP hammer pin. I suppose it's possible that the titanium firing pin could be a little out-of-round or too thin somewhere such that it may occassionally ride a little low and let the hammer catch it. If I ever get my lazy rearend up and make the long trek back to the range I will spend at least a few hundred rounds testing both firing pins. :) [%(]
Link Posted: 8/10/2003 5:17:03 PM EDT
ROS, OK, I'm assuming that your hammer looks like the hammer seen at the top right here [url]http://www.biggerhammer.net/ar15/hammers/[/url] I am also assuming that your bolt carrier looks like this [img]www.biggerhammer.net/ar15/barrelsbolts/sp1_boltassembly_later_bottom_moremetalmachinedaway.jpg[/img] and not like this [img]www.biggerhammer.net/ar15/barrelsbolts/sp1_boltcarrier_bottom_semi_notM16_159.jpg[/img] Am I on the right track?
Link Posted: 8/10/2003 7:07:20 PM EDT
Yes, Tweak, you are right in both cases. [%(]
Link Posted: 8/10/2003 9:42:36 PM EDT
[Last Edit: 8/10/2003 9:51:55 PM EDT by Tweak]
Dam, I'm good. OK, the ONLY options are that the ret pin is junk, too soft or something, or that the hammer is hooking the firing pin. Replace the ret pin. Look closely at the original ret pin, look inside the arc of the bend, use a loupe if you need to. You should see an indentation that matches the rear of the front spool on the firing pin. Then look at the hook on the hammer, look in the notch on the top front corner. You should see that the edge is chipped, or shiny where it has been catching the firing pin spool. You can bevel that corner to fix that. Run a probe down the ramp cut into the bottom of the bolt carrier, check that the probe doesn't hang up on the front of the firing pin collar. Have you compared the two firing pins? Checked the OD of the collars against each other? Best fix is to buy a shrouded (the bottom pic in the previous post) bolt carrier and use it. Closer to the original design weight too. [ed for specificity]
Link Posted: 8/11/2003 9:37:28 AM EDT
Tweak, actually when this happened I was far from home and another retaining pin so I just bent it back and did not encounter the problem again the rest of the morning, about 200 more rounds. Other than the normal striations on the sides of the front and back firing pin spools, the only indentation is a very small one on the side of the front spool just at the front lip. There are lots of striations on the side of the smaller rear spool and about 30 on one side of the front spool; not deep but light scratches. Is this not normal? As for the hammer, I see no chips or anything unusual on the front edges. I have run a probe down the carrier ramp and rotated the firing pin while doing so and find no way for anything to catch the front spool when it is fully seated. Its edge is about 1 to 2 mm deeper than the edge of the ramp. I've measured every dimension of both pins and the only difference is the front spool (collar) diameter is actually about .0001" smaller on the titanium pin. I was hoping to find it a bit larger, but didn't. Do you think the hammer is incorrectly dragging lightly on the side of the front spool and, one time, grabbed the side just hard enough to pull the pin back when the carrier came forward? If so, do you think I can shave the side of the front spool just enough the prevent the problem but not enough to not hold the retaining pin? Looking at Brownells catalog, I see three bolt carriers that all sound good but don't say anything about being shrouded. Do you have a particular one in mind? How does the shrouding help keep the hammer away from the firing pin? I can see how a lower angle on the ramp would help but don't understand the shrouding thing. Thanks for your help. I'm very interested now in the theory of this whole thing; this seems to be the best way to learn. [%(]
Link Posted: 8/11/2003 10:23:53 PM EDT
I think that, since you see no evidence of the hammer catching the firing pin, the most likely answer is that the ret pin is junk. Too soft most likely as I can't imagine a properly hardened part not breaking when bent to that degree. Have you had any instances of this rifle dropping the hammer when it shouldn't have? At any time has the hammer followed the bolt carrier shut? Were you firing fine then the bolt cycled and you couldn't pull the trigger? Most any damage to the front face of the spool is from contacting the rear of the bolt. Scatches in the area (between the rear and spool) that the retaining pin rides in are normal. I was asking if there were any circular indents in the retaining pin, these may be hard to see if you bent the pin back straight. The shroud on the bolt carrier fills in the ramped area on the bottom of the slotted carrier. There is no way that a hammer can contact the bottom of the firing pin with a shrouded carrier as only the back of the pin is exposed.
Link Posted: 8/12/2003 5:29:47 AM EDT
Tweak, the answer to your first three questions is no. The only problem this rifle has ever had is that one time when I had fired several shots and suddenly one time it wouldn't fire because the firing pin was floating free and I could hear it clanking around inside the bolt carrier. I understand now what you meant by 'shrouded' but have never seen a carrier like that advertised anywhere. It sounds like it would be tough on hammers as it would pull them back with much more sudden force than a tapered ramp would. I noticed that the carrier offered by Young Manuf. Co. in the Brownells catalog actually says "machined hammer ramp prevents damage to titanium firing pins". This makes it sound like this is a common problem. What do you make of this? Also, some carriers are advertised as being lighter than mil spec for competition use and others say one ounce heavier and increased bearing surface for smoother feeding and increased accuracy. This all sounds a little conflicting. I'm going to try to get out to the range this coming weekend and see if I encounter the problem again with the original firing pin and a new retaining pin. Again, thanks for your help. [%(]
Link Posted: 8/12/2003 3:49:34 PM EDT
The M16 uses a shrouded carrier, the hammer snag problems came into being with the Colt style (another anti FA attempt) slotted carriers. All advertizing is lies and I pay no attention to it. Use GI carriers and you'll have fewer problems. The carrier has nothing to do with accuracy, feeding, or competitiveness.
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