I can Think of LMT CMT Colt FN Bushmaster and DPMS for BCG manufactors.
Rob
I’m pretty sure Armalite nakes their own bolts. They have the deprecated lug design.
Good write up and pics.
The bolt in my BM is also stamped CM.
The feed ramps are not M4 cuts as shown above.
The key is neatly staked but not to the point of cutting into the bolts, more like clamping them, not sure why they chose to do it that way as a bit more force would have cut into them.
They provde a warning in thier catalog about having to key having to be staked to the carrier if buying a replacement.
It also states(claims) thier bolt carriers are MPI tested and mil-spec.
Ok, I’m not too informed about what MPI does or why its needed, can someone answer that? Also, from the sounds of things, what good does batch testing MPI do, it seems from the replies here that it makes no difference? MPI stands for magnetic particle inspection, right? So what exactly does that mean, and when can a gun assumed to be reliable if it was not individually tested?
Skintop911, great write up and review, very nice to see someone go over everything that is/isn’t up to par.
MPI, the short version
“Batching” means that they test samples from the various batches, not every single bolt. BM does this with both bolts & barrels, while Colt & LMT do it for every single sample.
So how useful is batch testing? Can a “batched MPI” bolt ever really be considered reliable or is the lack of individual MPI testing always a concern no matter how many rounds into the bolts life span?
Basically MPI looks for flaws in the steel. From talking with a couple different manufacturers, they have NEVER found a bolt that failed MP testing. Then again, none of these companies HPT either. What does this all really mean, well if your not HPT testing then, MPI really isn’t needed IMHO as you have not stressed anything. Another thing to consider is what are the companies acceptance criteria on their bolts (or barrels)? Zero tolerance for flaws? 1 flaw is ok? How bout 2? We don’t really know what they accept and what they don’t.
In a perfect world, I would buy 100 bolts from each manufacturer and have them all MP tested to see which ones have flaws and which ones do not.
A couple of the companies that I buy bolts from like to xray the steel used in long before it ever goes into production. This removes the bad steel early in the process and saves them money. I like this method a lot as well as they are removing the bad stuff before it ever has a chance to make it into the consumers hands.
If a company has a good QC program (like what I mentioned above), uses the proper steel and machnines the bolts properly, then I really don’t have any concerns if they do not HPT/MP test (YMMV). Does it hurt to HPT and MPI the bolt? No, not in the least. If a company makes sub par bolts then they should HPT/MP EVERY SINGLE ONE. Then again, this costs a lot of money and would take away from their objective (which is to make an $800 AR).
C4
I believe batch testing to be fine IF they have really good QC on the steel early on, use the proper steel (158 Carpenter) and are machining it correctly.
C4
Personally, I would always be concerned, but YMMV.
Obviously officers lives may depend on these carbines, why was the decision made to go with BM? Or do you know?
I have had one of the Texas DPS overrun uppers through my shop that had proper M4 feedramps as well.
Very uncommon though.
I believe that this was an individual officer’s carbine that skinstop911 was checking out from an armorer’s standpoint to get it approved for duty use.
I have feed ramps on my Bushmaster
Correct.
Ironically, the owner of this carbine was getting ready to write a check for a LE6920, but came upon this one from a local vendor. His resistance was weak. I didn’t have to tell him “I told you so”, the gun did the talking.
My department bought 10 11.5" barreled Bushmaster’s recently. Out of the three I’ve personally examined, one had M4 feed ramps, one had partially cut ramps and the other was a standard A2 spec upper. Two out of three had decents staking jobs and a black extractor insert and O-ring and one was staked and just had a blue insert like the one pictured . None of the three had a hammer like the one pictured.
Which model? How old?
How does yours compare to this one?
Regarding the hammer, is the general consensus that it does appear to be a casting?
I think I got it late 2001 early 2002 its post-ban the s/n is L268### if that helps. Its a XM15-E2S if you want I can post some pics?
I was under the impression that most, if not all, AR15/M16 hammers/triggers are cast. I know Sabre Defense has plans to produce MIM fire control groups because they feel MIM is superior to the usual cast units used in these rifles.
Very nice write up!