Maybe the supremely wise of this group can help steer me in the proper direction on my little situation.

The last time I went shooting, I was doing some
testing with my 2 AR's. Well, a bad thing happened that no one there had seen before. The bolt of my AR broke in the narrow area where the retaining pin fits into it.

Here's the real deal though:

1) this bolt carrier group is of uncertain origin

2) this upper was from DPMS that wouldn't headspace. As such, my smith did some machining of the chamber to allow it to headspace. He also had to enlarge the gas port of the barrel to get it to cycle mostly properly.

Here's what I'm concerned about. This upper has been a money hole (~$650 total) between the upper itself, headspacing and other stuff. Now, the hole is bigger. Also, I'm worried that if I get another bolt, I will run into more headspacing issues due to the above work having already been performed. Also, this upper has never quite worked properly, i.e. serious extraction problems that were somewhat remedied by enlarging the gas port, so I would like to improve the reliability somehow.

FWIW, I do have a float tube, a custom sling
attachment by my smith, and a stippled frontsight on the upper. At this point should I try to part it out just to cut my losses and start fresh with a new upper or should I continue to pour money into the upper?

Any thoughts? If I wasn't clear on something, just ask and I'll try to explain it better.

Wes

Here's more info:

The barrel is a 16" standard M4 profile 1x9 .223 from DPMS. I've shot with both short and standard length buffer assemblies.

The malf's I'm getting are a) leaving a spent round in the chamber b) pulling the spent round out far enough to cause a double feed with the next live round c) the spent round gets crunched by the bolt, and d) what I call a "phase-9" malf, the spent round gets caught between the bolt and/or key and the charging handle.

Would this be better in the trouble section?

Wes

Bolt sounds like it broke where most break, seems this only happens w/ "cheap non-USGI spec bolts" or one that's seen alot of FA fire.

As to the rest.....
Wish I could help ya, but there's too many odd things here:

1. [red]this upper was from DPMS that [b]wouldn't headspace[/b][/red]

Never heard of this from a factory DPMS upper, I'd have sent it back...

2. [red]my smith did some machining of the chamber to allow it to headspace[/red]

As the "barrel extension" mating w/ "barrel" determines the proper headspacing, why would gunsmith be modifying the "chamber"? (see chamber question below)

3. [red]Also, this upper has never quite worked properly, i.e. serious extraction problems that were somewhat remedied by enlarging the gas port[/red]

Sounds like a parts rifles, ya know part from here, a part from there, oh... this bolt cheaper, I'll take it.....

I'd be willing to bet money there was nuthin wrong w/ the gas port to begin with.... as I have heard of no problems w/ DPMS M4 barrels and there have been quite a few sold by MSTN/CMMG and others on the Equipment Exchange, (ya think we'd have heard something by now), suspect problem w/ bolt carrier, bolt, extractor and ejector related to begin w/ or ya've got a non-spec upper/FN reject.

As to theses problems:
[red]The malf's I'm getting are a) leaving a spent round in the chamber b) pulling the spent round out far enough to cause a double feed with the next live round c) the spent round gets crunched by the bolt, and d) what I call a "phase-9" malf, the spent round gets caught between the bolt and/or key and the charging handle.[/red]

I'd replace the bolt w/ a mil-spec one from Bushmaster or DPMS (I use their parts and have had no problems, w/ their lower kits or complete b/bc's), maybe your problems will be gone, if their not I'd suspect my gunsmith already screwed up my rifle by altering the gas port to begin with.

I am understand your post correctly, in that you started this project w/ a new DPMS M4 1/9, 16" barrel, correct?

and this barrel was chambered in 223 or 5.56?

Please take this w/ a grain of salt, but I trust the gunsmith who does work for me now, he's tops, but until I met him, I wouldn't trust a gunsmith further than I could pitch him/her..... as I had been screw'd, by more than a few who didn't have a clue, some who messed up trigger jobs, a relatively simply chore for most. And I still run into supposed "AR" smiths who when question'd reveal they know nuthin 'bout how an AR operates.

While your's may not be in the "bad" category, suspect too many ???s above mean accurate diagnosis of your AR cycling problems will be an exercise in patience on your part and require detail explainations on how this rifle was put together.

BTT for other advise....

Mike

BTW - please don't consider me "supremely wise" as sometimes, I have trouble findin my butt with either hand........  

My experience is that the only bolts you can be positive have been elctropolished to "break" the sharp edges around that hole to pretty much eliminate the risk of cracking are Colt, and GI surplus used pieces.  Can't comment on Bushmaster or DPMS, since I haven't examined the bolt assys of either, but the DPMS lower I just bought had a totally out of spec bolt holdopen and a couple of other not quite right pieces, so I don't think I personally would order a bolt from them.

Bushie may do the same electropolishing that breaks the sharp edges around the hole, and the bolt face. If so, fine.  It's those sharp edges that is causing the breakage at the hole, and shaving brass off the rear of the case around the bolt face.  Personally, I found a source for used GI bolt assys awhile back, for $20 apiece, and bought four of 'em. Now, all my ARs have Colt bolts.

Found the bolt assys at [url] www.sunsetguns.com[/url]. They may still have some. Three of the four I got were fine for headspace in all of my ARs. The fourth closed on the GO guage, but not on the FIELD guage, so it's a spare.  Replaced the extractor springs w/ HD types from Wolff gunsprings, and they work just fine---and I don't worry about cracked bolts[:D]

Thanks for the thoughts and tips fellows.

mr_wilson,

The reason that I didn't send it back to DPMS was cost. By the time I sent it round trip, plus a cost of a new bolt or other parts it was about the same as letting him work on it.

As for the upper, it was factory assembled from DPMS, except for my bolt carrier group and charging handle. After the headspacing problem was "remedied" the gun wouldn't function, lots of short-stroking. Probably 25/30 rds. of a mag would have some kind of malfunction.

After enlarging the gas port, the malfunctions were reduced to something like 3-8/30. Lots better, but still not good.

I don't really know what else to say.

Wes

I'll give it another shot, [b]"was this upper chambered for 223 or 5.56?"[/b]

(Understand there are small chamber differences which CAN cause a 5.56 round to stick in a 223 chambered rifle, this is why I asked above and am asking again....)

Was the bolt/bolt carrier installed "NEW" or "used"?

If used, was answer above, how used? 1000 rounds or less, more than that? more than 5000 rounds?

(bolts can take a set, when used exclusively in one upper, and as a rule most do not swap bolts and carriers between different uppers, this is not a hard and fast rule, just generally as most ARs/M16s are designed to be able to swap b/bcs without headspacing problems, just trying to rule out things here)

How was rifle determined to be outta "headspace"?

(go/no go gauges, field headspacing gauge, or done by gunsmith and ya don't know...)

DPMS is responsible for the products they sell, if the upper was outta spec, for your own benefit as a consumer, Cya should have made them fix it, (perhaps they had a problem they weren't aware of, could happen...)

What was size of gas port originally?

What size did gunsmith ream it to?

(Note that according to various sources, Colt's gas port sizes are:  
[10.5" - .093]    
[11.5" - .081]    
[14.5" - .063]    
[16" - .063])

Answers to these question will help immensely.

Mike

mr_wilson,

The barrel was marked ".223."

The bolt carier assembly was used and of unknown origin and # of rounds.

On the headspacing, it wouldn't even take a "go" gauge. I saw that myself.

The port size I think was something like .05" if I remember correctly, but I could be completely wrong. I thought he opened it up to .09, but I could again be wrong.

Sorry to miss the questions the first time around. I think I answered them as best I know.

Wes

[b]The barrel was marked ".223."[/b]

From chart below, although marked "223", believe your rifle upper was a 5.56 chambered barrel, which precludes and 5.56 in 223 chamber issues.....
[img]http://photos.ar15.com/ImageGallery/IG_LoadImage.asp?iImageUnq=3425[/img]

[b]The bolt carrier assembly was used and of unknown origin and # of rounds.[/b]

NOT a good thing, partywagon, ya spent hard earned money for a "new" DPMS upper, then install a b/bc which is USED and with no idea how used. This was not a good thing.

[b]On the headspacing, it wouldn't even take a "go" gauge. I saw that myself.[/b]

While hind-sight is always 20-20, here's where one should discard the "used b/bc" and get a new one from DPMS. (sure that just what ya wanted to hear...)

[b]The port size I think was something like .05" if I remember correctly, but I could be completely wrong. I thought he opened it up to .09, but I could again be wrong.[/b]

As chart shows above .09 might be too big, but given "used parts" above, have no way to tell if this is a contributor to your present delima or not...

While I still feel a "new b/bc" is the best way for ya to go, I can certainly understand your frustration over rifle that won't shoot reliably.

For those reading this:
Should ya have any problems w/ products, (uppers/lowers/trigger groups/barrels, whatever) which you purchased [b]NEW[/b], return them to the purchaser for repair or replacement. [b]You have the right as the purchaser, to quality[/b], but only if [b]you[/b] demand it!

IMHO, never use a "USED" item unless you are certain of it's use (ya may end up w/ a b/bc that's had untold numbers of rounds through it all in FA, or it may be a part of substandard quality). I never buy a new upper without installing a new B/BC/CH, not that the CH matters but IMO the b/bc do, cus I want 100% reliability, and yea, best to always check the headspacing, although in my experience I've never found one out....YET!

Sorry for your predicament, party, wish there was more that I could suggest or help w/ but sometimes learning things the hard way helps w/ decisions later on in life.

Good luck w/ your DPMS, I know their decent rifles as I've seen too many that shoot well, hope ya get that thing runnin, e-mail if I can help,

Mike  

Mike,

Thanks for the insight. I've pretty well decided that $50 more is worth it to give it one more try. Fifty is how much a new, assembled bolt is from Bushmaster. If that doesn't take care of it, I'll probably just part out the upper.

Wes