I've got about 500 rounds thru' a Colt 9mm SBR, and thought I'd give it a good cleaning.
When I removed the firing pin, there was a slight burr on the tip, and what seemed an unusually large amount of dirt in the firing pin channel.  I gave the channel a good cleaning, smoothed the burr with crocus cloth, and ordered a new firing pin from Brownells.

The real question; what caused the burr?  Is crud in the FP channel common in these carbines, or was I experiencing some primer perforation due to the burr?  

Also, I've been running an SSA in this carbine; it's worked just fine.  
An article in a gunzine stated that the Geissele trigger wouldn't work in another brand of 9mm carbine; any thoughts on this in the Colt?

Finally, I have a spare firing pin on order; are there any other nonstandard AR parts that are worth keeping on hand for the Colt?

Thnx,
Moon

I have run an Geissele SSA, and do run an ALG ACT, in a Colt 6951 (16" flat top 9mm); also, an SSF in a Colt 614 setup with a 9mm with a Hahn conversion.
All these triggers work just fine in my Colt's.

No idea about the burr, maybe it was there all along?

Spare parts... It wouldn't hurt to keep some of the cheaper small parts on hand, especially since you're going to order something already.

Thnx for the comeback; really felt the SSA was just fine, but I thought I'd ask.  Mine has run perfectly.

You may be right about the burr being there; I can't imagine what could have created it.  Is a lot of dirt in the firing pin channel common with this design?  It didn't affect function.

What else is nonstandard in the 9mm?  I'm thinking I should have ordered an extractor while I was at it, but didn't think of it.
Moon

Can you quantify "a lot"?  How does it compare to a DI 5.56 rifle?  My guess is a blowback rifle could get dirtier than a DI rifle, and don't worry about it.  It's a gun, not silverware.

Maybe someone at Brownell's could help you figure out what parts to keep on hand?  I guess it would depend on your budget too...

There was more crud in the FP channel than I expected, and certainly more than the DI ARs.  I'm not terribly concerned about it; just wondered if the burr had anything to do with it.  The brass that was most recently thru' the gun has already been tossed in the 'to be reloaded' can, so I can't examine that for damage to primers.  I did notice that brass that had been thu' the gun the other night was dirty; figured it was the blowback operation.
Brownells is a good suggestion for tips on parts; I have spares of most of the smaller standard AR parts, but the firing pin surprised me in that Brownells was the only source.  Colt doesn't stock them.  I talked to a tech online at Brownells (and he was extremely helpful) to locate the firing pin.  I may touch base with them and ask the question.

9mm blowback ARs are FILTHY.  It's the nature of the cartridge and the blowback system.  Almost all of the crud is sooty rather than the kind of baked-on crap you get on bolt tails in a DI AR.  Yucky but not a real problem.

No telling where that bur came from.  It could have been from a number of issues, including a manufacturing defect, a leaky primer, or "other."  Having a spare firing pin isn't a bad thing, but I'll bet the old one will work fine once you removed the bur.

Some 9mm bolts are profiled differently from others.  If the rear of the bolt, especially the ramp, is as close as possible to the profile of an M16 carrier, then any hammer that looks close to an M16 hammer will work fine.  (The trigger itself isn't relevant, just the hammer profile.)

The 9mm bolt has a couple of odd roll pins, the extractor is unique, and you may want to get a spare ejector and ejector pin.  Not that any of those pins are likely to fail on you, but having them in case you have to replace the extractor or ejector (which might actually fail after a lot of use) isn't a bad idea.

Good tips, GH.  Concur about the soot being about easily dealt with, and not a problem.  The damned thing is a ball to shoot, and cheap to feed with reloads.  It's been stone reliable; I'd take it in harms way if it ever came to that.
I'll have a long look at the ejector, but a spare extractor is on my short list.  The rest of the gun seems pretty much standard AR; even the recoil spring is supposed to be the same.
The more I think about it, the more I suspect that the burr on the FP was a factory defect; it was sharp edged; I can't imagine a primer burring it.
Thnx, guys,
Moon

Remember that the ejector is part of the block Colt pinned into the lower receiver.  It's that piece that sticks up on the left side.  That puts the ejector out in the open when you have the upper off the lower, which is why I suggest thinking about a spare.

GH, understand about the ejector; it's a pretty stout piece, but your suggestion that it might be buggered while the gun is taken down is entirely possible.  Frankly, I think the extractor is the more likely of the two to fail, but I'm trying to get both, along with the roll pins that secure them.

But there is a problem.  Talked to an online chat guy at Brownells; the only thing he was able to find was a CMMG bolt rebuild kit; not sure if that is compatible with Colt.  I have a message in to Brownells tech support to see if they have better info.
Any other notions of where to look for the extractor/ejector?
I'm giving some serious thought to a supressor as well, but we'll save that conversation for later..
Thanks,
Moon

Okay, had a second conversation, on the phone, with another tech at Brownells.  The actual Colt extractors are available from Brownells.
I've a parts number if needed.
Moon