Some (Very) Brief Notes on an AR-15 Tech Inspect Clinic

[Jay Cunningham]

The chambers on a DPMS and a Palmetto carbine failed to gauge properly on a 5.56mm NATO go/no-go... both had their tight chambers reamed to true 5.56mm. Both barrels were marked "5.56mm"... go figure.

The DPMS had out of spec gas rings, which were replaced (thanks SeanM your box of pieces parts is still making the world a better place).

Neither the DPMS nor the Palmetto had worthwhile markings on their bolts; I recommended replacement bolts of a known quantity.

Both the DPMS and Palmetto were carbine gas systems with 16" barrels, however they both had CAR buffers, which I consider suboptimal for that configuration. I recommended either H or preferably H2 buffer replacement.

The DPMS had no staking at all from receiver end plate to "castle nut", which I repaired with a spring-loaded center punch.

Astonishingly, both the DPMS and Palmetto guns had decently attached and staked carrier keys. Both also had proper inserts in the extractor spring. The Palmetto had both M4 feed ramps and barrel extensions, and the DPMS had rifle ramps/rifle extensions. This was fine for the A1 configuration.

After these tweaks, proper lubrication and function checks, both guns ran without issue and exhibited good accuracy.

[Redhat]

The chambers on a DPMS and a Palmetto carbine failed to gauge properly on a 5.56mm NATO go/no-go... both had their tight chambers reamed to true 5.56mm. Both barrels were marked "5.56mm"... go figure.

The DPMS had out of spec gas rings, which were replaced (thanks SeanM your box of pieces parts is still making the world a better place).

Neither the DPMS nor the Palmetto had worthwhile markings on their bolts; I recommended replacement bolts of a known quantity.

Both the DPMS and Palmetto were carbine gas systems with 16" barrels, however they both had CAR buffers, which I consider suboptimal for that configuration. I recommended either H or preferably H2 buffer replacement.

The DPMS had no staking at all from receiver end plate to "castle nut", which I repaired with a spring-loaded center punch.

Astonishingly, both the DPMS and Palmetto guns had decently attached and staked carrier keys. Both also had proper inserts in the extractor spring. The Palmetto had both M4 feed ramps and barrel extensions, and the DPMS had rifle ramps/rifle extensions. This was fine for the A1 configuration.

After these tweaks, proper lubrication and function checks, both guns ran without issue and exhibited good accuracy.


Just for my education, what is the current "proper" extractor spring/insert combo?

[Jay Cunningham]

The black insert is appropriate for carbines.

[Wayne Dobbs]

Jay,

I've seen about a dozen DPMS M4gery carbines that failed gas ring tests right out of the box (all of them). Replaced gas rings and they still failed. IOW, had overbored bolt carriers. With regard to "5.56 NATO" barrel markings, I've learned that unless the barrel is a Colt, BCM or LMT, it's likely fiction. I use Ned Christiansen's NATO chamber gauge and reamer to handle all the others.

[Chuck Haggard]

I was issued a Bushampster M4gery at work, I had to ream the chamber to 5.56 and drop in a Colt BCG, after that it ran fine. We had several that had to be fixed right out of the box.

[Jay Cunningham]

Wayne, I was concerned that the inner dimensions of the BCG would be out of spec, but gas ring replacement passed the "drop" test.

Interestingly enough, the owner of said DPMS had a past bad experience with a stuck case. Hmm... your chamber was too tight, and your bad gas rings were probably contributing to less-than-robust-cycling...

[Jay Cunningham]

I have Ned Christiansen's chamber reamer, go/no-go gauge, and MOACKS. The guy is a mad genius.

[Wayne Dobbs]

I have Ned Christiansen's chamber reamer, go/no-go gauge, and MOACKS. The guy is a mad genius.

He is for sure. I recommend his products to all the armorer classes I teach for Colt so that those guys can deal with the "other" ARs they have in service.

[Mike C]

Jay out of curiosity which PSA kit/carbine was it? Was is one of the lower end PTAC, Blackhawk kits or was it one of their, "premium kits?"

[johnnyreb™]

Mike C

It was this one. http://palmettostatearmory.com/index.php/catalog/product/view/id/2279/category/313/

[Jay Cunningham]

Jay out of curiosity which PSA kit/carbine was it? Was is one of the lower end PTAC, Blackhawk kits or was it one of their, "premium kits?"

Sorry I missed your question, but you got your answer right from the horse's mouth so it's all good.

[Byron]

Jay,

If you don't mind sharing, how many rifles did you inspect through this clinic?

Were the DPMS and Palmetto the only two with functional issues, or were they just particularly noteworthy?

[Jay Cunningham]

This was a small clinic with only three rifles; the other one was squared-away.

However, I've dealt with DPMS, Bushmaster, and Palmetto on a recurring basis.

[Byron]

Thanks, Jay