what's chewing up my firing pin??

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[ARCHIVED THREAD] - what's chewing up my firing pin??

Posted: 1/2/2004 3:34:21 PM EDT

Ever since I put my new 16" BMI upper on an older BMI lower my firing pin is getting chewed up. The area that's getting abraded is where the pin curves or rounds over and transitions into the shaft going back towards the rear of the pin. Is the hammer riding at this point on the "bell", for lack of a better desriptive word, and roughing it up??

I don't know if I described it very well.

Does someone know what's happening??

and more importantly, how to correct it??

Thanks in advance for any and all help.

Posted: 1/2/2004 5:32:55 PM EDT

[#1]

It the back of the bolt has a edge, and leaving a indent ring at the collar of the firing pin, then you can use your thumb with a sheet of 400 sandpaper and roll sand the edge off.

If you mean that the outer section of the collar is getting chewed to hell, chances are the the back of the carrier has chatter marks from the end mill, and is waht is doing the damage. Since the carrier is heat treated, you not going to be able to sand the chatter out, and will have to live with the shortened life of firing pins.

Posted: 1/2/2004 6:12:11 PM EDT

[#2]

not either place.

start at the flat surface of the firing pin that abuts the back of the bolt. From there travel back towards the end of the firing pin. The first radias after the flat part, where it transitions to the firing pin shaft before the end bell/knob, is where the wear is occuring.

The outer edge of the "bell" after the flat of the collar is getting abraded.

I wish I could draw a picture for you.

I'm sorry me description is lacking.

Posted: 1/2/2004 8:11:03 PM EDT

[#3]

Boog

You may have an M16 firing pin. It has a colar that's .375" in diameter if memory serves. The AR15 has a smaller diameter (.330").

The AR15 carrier is grooved to allow the notch on the hammer to catch the firing pin and prevent 'slam fires'.

Posted: 1/2/2004 9:19:43 PM EDT

[#4]

If you mean that the outside face/ bolt side of the collar is getting gnarled up, then chances are that the hammer is catching the firing pin as the carrier travels forward during the cocking stroke.

To solve this, radius file the top edge of the firing pin contact pad of the hammer. This will allow the firing pin to glide over the collar, instead of getting caught and taking small bites out the collar as it slightly binds.

P.S. A photo would really help, instead of trying to guess where the damage is being done.

Posted: 1/3/2004 1:03:27 AM EDT

[#5]

[url=http://ar15.com/forums/announcement.html?b=3&f=66&id=185]FAQ II[/url]
Check [b]Damage to firing pin retaining pin[/b]

Posted: 1/3/2004 9:57:22 AM EDT

[#6]

This appears to be what is happening.

I'm trying to import a .gif pic of a hammer with the area that I think needs to be radiased outlined but am having trouble figuring out how to. I don't have a digcam so I can't upload a pic.

I've looked in the help files and they are no help.

I'm sorry to put you guys through all this trouble, but can someone get a pic of a hammer up and outline/highlight the area or edge that I need to smooth out?

I see a shiny spot on the top corner opposite the "hook" of the hammer where I beleive the firing pin is rubbing, but I'm hesitant to just start smoothing things out unitl I know for sure which area to smooth.

Posted: 1/3/2004 12:54:52 PM EDT

[#7]

Quoted:
The AR15 carrier is grooved to allow the notch on the hammer to catch the firing pin and prevent 'slam fires'.

View Quote

I thought the AR firing pin had the larger collar to catch the hammer?

Posted: 1/3/2004 11:13:46 PM EDT

[#8]

The M16 has the larger collar. The hammer will catch even the small collar of the AR pin if the hammer follows. The larger collar of the M16 pin will catch ANY time the hammer is resting on the sear face of the trigger.

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19405[/img]

M16 pin on right.

ETA,

The diameter of the spool wasn't an issue until the ramped carriers came into use.

Posted: 1/3/2004 11:20:04 PM EDT

[#9]

Quoted:
but I'm hesitant to just start smoothing things out unitl I know for sure which area to smooth.

View Quote

Just replace the bolt carrier with a correct (read, "non slotted") bolt carrier.

Posted: 1/4/2004 6:36:49 AM EDT

[#10]

I went ahead and gently smoothed out the upper edge of the contact pad, and the edge right above that also with some 1000 grit wet/dry. I saw that these were the surfaces that were bearing on the spool of the firing pin as the carrier was cycling. I then saw your post Tweak. I don't think I caused any damage or problems to the action, but will get a non-slotted carrier soon.

I am assuming I can use a Colt bolt carrier in my Bushy, correct??

Posted: 1/4/2004 2:58:23 PM EDT

[#11]

Thanks for the clarification!

Posted: 1/4/2004 10:04:47 PM EDT

[#12]

Quoted:
I don't think I caused any damage or problems to the action, but will get a non-slotted carrier soon.

View Quote

I doubt that you did either. A non slotted carrier is simply the more elegant answer. You can use a Colt carrier in your BFI.

Posted: 1/5/2004 6:08:08 AM EDT

[#13]

thanks tweak.

Posted: 1/5/2004 3:08:05 PM EDT

[#14]

It's cheaper to just remove your hammer and grind off the little "V" notch at the upper forward corner of the hammer. Grind a nice smooth rounded contour so it won't snag your firing pin as the carrier assembly moves forward over the hammer. Use a little B-C cold bluing to restore the finish on the bare steel.

Posted: 1/5/2004 3:49:21 PM EDT

[#15]

Thanks for the input. Since this is happening on a new (2 months old) BMI 16" upper that I bought from Bushmaster. I have contacted them regarding this and they have given me an RMA number to return the bolt carrier to them for evaluation. I told them up front that I would like a shrouded bolt carrier and for them to keep the original one. They said they would see what they could do. I'll return it to them with the cautious hope that they will trade it for a shrouded bolt carrier.

Posted: 1/11/2004 4:54:10 PM EDT

[#16]

Quoted:
The outer edge of the "bell" after the flat of the collar is getting abraded.

View Quote

Borrowed a camera this weekend. Is this close to the damage you describe?

Worn firing pin / New firing pin
[img]http://www.imagestation.com/picture/sraid99/p48e28d6799ac8b5c61d8e8960a3894dd/f9fb7b29.jpg[/img]

Cut away bolt carrier with worn/beveled firing pin installed
[img]http://www.imagestation.com/picture/sraid99/pdf57895320f597f15c1ca57254959a44/f9fb7b35.jpg[/img]

Posted: 1/11/2004 5:13:07 PM EDT

[#17]

Yep. That's pretty close. Mine was a litte rougher. I sent my bolt carrier back to BMI and I'm pressing them for a shrouded bolt carrier. I'm going to call them tomorrow and see what they say.. They should have received my bolt carrier last Thursday.

Thanks for the picture.

Posted: 1/11/2004 9:08:20 PM EDT

[#18]

Why worry about it ? This is fairly common with some ramped bolt carriers and is caused by the firing pin shoulder riding the hammer as the carrier moves back after firing . It won't cause the firing pin to fail .
The ramp is there to prevent hammer follow ( hammer will hang up on firing pin shoulder preventing the bolt carrier from going into battery ) and subsequent FA fire if your disconnector fails or your match way 2 light trigger goes south...

Posted: 1/11/2004 10:02:07 PM EDT

[#19]

Quoted:
Why worry about it ?

View Quote

If you follow the link I provided all will be clear.

Posted: 1/11/2004 11:30:33 PM EDT

[#20]

Still wouldn't worry about it !
Boog's isn't doing what your faq link says.

Posted: 1/12/2004 6:11:34 AM EDT

[#21]

If the hammer is snagging the firing pin then there is a good chance that the firing pin is striking the firing pin retaining pin. In this case the contact looks to be slight but there is still unecessary contact.

Boog,

If you slowly let the bolt forward with the charging can you feel the bolt carrier bind? Do you see any flattening in the center of your firing pin retaining pin?

Posted: 1/12/2004 8:48:40 AM EDT

[#22]

I'll be damned. Mine does the same thing, including catching as the carrier goes slowlt forward. It will aslo, if the carrier is "ridden" forward, stay on the disconnector, unless the rifle is bumped, when it will then drop to the sear.
For a point of info, I have a Colt carrier, non-slotted, with the ramp and a large shouldered firing pin.
Thanks for the info guys, I now have something to deal with.
BTW, the rifle has always functioned flawlessly, but I believe that any potential failure should be dealt with if possible.

Nick

Posted: 1/12/2004 9:02:56 AM EDT

[#23]

Tweak,

When I ride the charging handle forward I can feel a kind of grinding roughness for the first couple of inches and then it smooths out. When I pull and hold the trigger and do the same the effect is the same. I also checked my firing pin retaining pin and saw very, very slight flattening and a shiny spot where the fireing pin spool has been hitting it. After starting this thread I did smooth out the surfaces of the hammer that were bearing on the underside of the BC and the spool of the fireing pin a bit.

The rifle functions fine. No failures to feed, fire, extract or eject in about 800 rounds after I got my initial extraction problems resolved.

I'm pressing BMI for a shrouded bolt carrier. We'll see what happens with them.

Posted: 1/12/2004 9:08:05 AM EDT

[#24]

C_G,

Does the bolt hang when you run the bolt forward while holding the trigger to the rear? You said you have a Colt "non slotted" carrier. Do you mean one that looks like this?
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=16192[/img]

Posted: 1/12/2004 9:43:31 AM EDT

[#25]

Yes, that is exactly the carrier I have. My firing pin, however, is a larger spool, and has the same damage that Boog's has in his picture. Tried running the carrier slowly again, with trigger held and without, and "catch" does not happen consistantly. It could be the charging handle hitting the back ridge of the upper receiver-kind of hard to tell.
Upper receiver has a lot of play at the takedown hole, and sometimes the upper sits above the top of the lower receiver.
The catch is just before the bolt gets to the barrel extension.

Nick

Posted: 1/12/2004 11:30:45 AM EDT

[#26]

That's a slotted carrier in the pic C_G. The good (shrouded) carriers look like this
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=16191[/img]

If you run an M16 (large collar) pin in a slotted carrier the collar will snag every time the bolt cylces. Replace the pin or grind (belt sander works fine) the collar down.

Posted: 1/12/2004 12:04:34 PM EDT

[#27]

Thanks.

Nick

Posted: 1/12/2004 12:23:50 PM EDT

[#28]

Well, I just spoke with Bushmaster. They said they gave me a replacement BC that is shrouded to protect the firing pin spool from the damage I was seeing. I should receive it sometime late this week.

As far as grinding down the collar/spool of the firing pin, should the new diameter be .330, as previously stated???

Posted: 1/19/2004 5:34:27 PM EDT

[#29]

Just got a new replacement *shrouded* bolt carrier from Bushmaster. I thought that maybe they were going to blow me off and just send another slotted one but to my surprise and satisfaction they sent me a shrouded one that looks just like the one above in tweaks post.

The only thing I noticed is that when I ran the new BC, without the bolt, into the upper to check for alignment between the key and the end of the gas tube I noticed a very slight resistance when the key and tube contacted that went away as the carrier slide further. I think it's just a new BC and key that needs to "fit itself" to the gas tube by shooting it a bit.

Thanks to all who responded and especially the tweakmyster.

thanks tweak.

Posted: 1/20/2004 4:45:30 AM EDT

[#30]

The gas tube may need some adjusting to fit the new key/carrier combo. "Shooting it in" may lead to unecessary wear. You should be able to slide the new carrier (minus bolt) forward with an absolute minimum of effort. The whole assembly should slide shut and lock when the upper is held at about a 45 degree angle.

Posted: 1/20/2004 6:03:42 PM EDT

[#31]

As I understand it, applying a slight amount of pressure to the end of the gas tube in the desired direction will accomplish the adjustment correct??

basically, gently bend it??

Posted: 1/20/2004 6:52:37 PM EDT

[#32]

I gently "tweaked" it in the direction I thought it needed to go and when I hold the upper at 45 degrees and let the BC slide forward it slides into place.

I only hold the BC about 2 inches out from the back of the receiver and it slides into place with no delay.

It "clanks!" into place very nicely.

[ARCHIVED THREAD] - what's chewing up my firing pin??

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