I recently sold a Bushmaster DCM upper that I had in the safe for two years and never used. The purchaser has stated it fails to feed about every 3rd round. I know nothing about diagnosing AR issues.

Anyone care to make suggestions I can pass on?

Was this a complete upper assembly or just the upper receiver?

My guess is this dumbsheet didn't know what the hell he was doing when building his "project rifle" with this upper!

Have him describe in detail how he put his "Rube Goldberg" rifle together and EXACTLY what's going on "malfunction wise"!

If you know the upper is new from Bushmaster, the upper is NOT the problem!

Complete upper assembly with matching bolt as sold by Bushmaster, although I did buy it used. I did a little bit of research before I purchased this upper and confirmed with a local AR-15 celebrity after in my possesion. I told the buyer I would try to get him some help, but not knowing what kind of ammo or whether he thoroughly cleaned and lubricated components before firing makes it difficult IMO.

quote:

Originally posted by drewhenrytnt:
Complete upper assembly with matching bolt as sold by Bushmaster. I did a little bit of research before I purchased this upper and confirmed with a local AR-15 celebrity after in my possesion. I told the buyer I would try to get him some help, but not knowing what kind of ammo or whether he thoroughly cleaned and lubricated components before firing makes it difficult IMO.

I saw your ad and photos in the AR classifides. I don't think it's a "clean and lube" problem. More likely the guy's "operator headspace" problems!

drewhenrytnt, I see you're trying to do the right thing with this guy..... but if he isn't smart enough to diagnose the problem (or provide enough info that someone else can help him diagnose the problem)..... that's all you can do!

The price was EXTREMELY fair!

going to be an ammo or magazine issue more than likely.

I have a history with the upper in question I believe I'm the one who sold it to drewhenryhunt, So, if it is the one I sold to him, I will state for the record it functioned very well when I owned it, but, it needed to be kept very clean to run well. And, it needed decent ammo, no Wolf or similar junk.

Could be many things the last one I fixed the front gas block was loose and wasn't allowing enough gas to operate the action.

One would almost have to have it in hand to make sure what it was.

Bad mag,bad ammo bad fit betwwen the upper and lower. what brand lower was it. If it is a colt lower there could be a take down pin hole size differant.

Da Man, go screw yourself.

To others, I bought the upper and I am not in any way saying it's defective. I asked the seller if he had encountered any issues hoping I could save some time before delving into it. I'm not looking for him to take it back, I shot it, it's mine.

It was put on a JD Machine lower that is a known performer.

I cleaned and lubed with CLP before shooting, and was running PMC Bronze and Winchester USA ammo. Using both pmags and standard AR mags produced similar results. I think the aluminum mags were bought from Rock River, though I don't recall for sure.

Brass was ejected anywhere from right next to the bench to about 8 feet away. Like the op said, about every 3rd round would fail to feed. The case would almost get free of the mag, but not quite.

Fit between the upper and lower is very tight, no play at all.

The stock is an A2 with a relatively new buffer and spring.

I'd appreciate any insight.

Here's a goofy prob I had with colt pre ban I bought new for $440 in late 80's. I had run 3-4 thousand rounds through her over the years; then started having problems. I figured just dirt & carbon, but after many tear downs, I ended up taking to gun shop, then another, then another; nobody could fix it. So I finally took it into protec in fairbanks, told bill that I'd see him nx Spring and I wasn't taking gun back until he had fired 50 rounds through her. Sure enough, after 30 rounds, acted up after he had replaced springs, extractor, ect. It was the bolt carrier. Looked like it was worn on bottom side. Whatever, it worked fine after replacing bolt carrier, and has went through 500 rounds since. So maybe swap a bolt carrier for grins.

Kind of like process of elimination, but first thing I would do is examine the gas rings on the bolt itself, even replace, cheap and quick, also make sure the "key" is tight on the top of the carrier. Usually those are torqued and staked in place, but have seen them loose if not staked?? Might mention that in the event the rings are lined up where the gap is open for all three, alternate them for a better gas seal. Better still get one of those one piece gas ring(McCormick??) instead of the three for dependability.

I run a pipe cleaner through the gas key hole/tube from time to time just to make sure it is open as it should be to operate correctly. As mentioned earlier, would also insure that the front gas block is tight, lined up and the gas tube is seated in the gas block.

Since you have tried mags, using std. A2 lower w/ appropriate recoil spring/weight system, used different ammo the gun should run. Trying a different carrier is not a bad idea either for have seen a change there solve a problem as mentioned. Keep us posted on results, am sure there is a fix out there, just have to find it.

The more you mention of the trouble sounds more like a gas problem. I would give the whole gas systm a good going over front to back. looking for something blocked, bent,loose,worn, dirty, out of place.

CasII
that is weird...when I shot it, it would make a neat little pile of brass, I could put a 5 gallon bucket on top of the first piece of brass and the rest would just about all hit the bottom of the bucket.
it has been mentioned, but check the gas rings on the carrier, also, make sure the cap screws are tight, seems like I remember using some red locktight on the carrier because it came loose on me once.
Let us know when you find out what it is, sounds like you are familiar with the platform, but check all the simple stuff first.

good luck

Bore scope the Bbl to ensure the gas holes are aligned w/ the gas block.
Tighten the bolt carrier group gas key allen head cap screws & stake.
Inspect/relieve the 9 o'clock bolt lug aft end .010".
Install McFarland 1pc gas ring on bolt.
Inspect/Deburr the aft end of the bolt lugs.
Cycle the bolt/carrier group into the Bbl extension by hand to ensure smooth functioning.

Sh!t Can any plastic magazines.
Use quality 223/5.56 ammo to function check.

If the gas ports aren't lined up there isn't a whole lot he can do being that has the original AR15/M16 front sight/gasblock and it's pinned.

I'd leave the bolt lugs alone unless you really know what you are doing. That relieving the lugs opposite the lugs adjacent from the extractor side of the bolt come from Armalite to prevent the bolt from tilting during firing to relieve the uneven pressure going to those two extractor adjacent bolts.

If the key has come loose before that is a possibility. Again it's a tad hard to stake those screws if you don't know what you are doing. It may be better if you clean the screws and holes of oil and red LocTite them.

Someone mentioned the gas rings on the "carrier". The are on the tail of the "bolt".
Rarely do you see gas rings go bad on a new setup unless they were defective to begin with.

I went through and thoroughly cleaned every single part of the bolt and carrier. There is no obstruction in the gas key.

I have not switched out the gas tube, but will if I have to.

The gas key appears to be staked and appears to be very secure. No movement at all.

The only thing that jumped out at me was that the top of the tail of the bolt was pretty severely pitted.

The entire upper was lubed again with CLP, and it appears to function perfectly when I cycle the action by hand using the charging handle. It runs through all three magazines without a single hiccup. This tend to lead me to the conclusion that it is not the magazines.

So, I took it to the ranch this morning to try out again, and had this:







I took three different magazines, 10 rounds each, and had an average of 7 FTF per magazine. Again, brass was all over the place, from less than 24" from my feet to more than 9 feet away.

This was all brand new, recent manufacture PMC Bronze ammunition.

Just to make sure, I also brought along a Stag Arms Varmint upper and ran the same ammo and mags with no troubles at all.

Okay, being you have two AR15's to play with let's play switcheroo. First put the Stag bolt/carrier group in the Bushmaster and shoot it. See what happens. If it runs fine through all the magazines it's not the bolt/carrier group. Next put the Stag buffer and spring in the Bushmaster. Same routine. I think you will narrow it down then. Just keep switching things around see what happens.

Scattering empties all over the place is definitely telling us the bolt is coming back at different velocities, so something is holding it up. Could be a gas problem, a buffer and spring problem, a binding problem. You could also put the Bushmaster upper on the Stag lower.

Oh yeah, in the pictures is that an empty case or is it a loaded round that didn't chamber?

Report back your findings.

All of the pictures are of loaded rounds that did not chamber.

I only had one lower today, and switched between the two uppers. I do have another lower, though it is set up for a carbine. I could probably borrow another A2 buffer assembly form a buddy.

Thanks, I will swap bolt carrier groups and re-try tomorrow.

Okay being that was a loaded round trying to chamber I'd say your bolt/carrier group isn't coming back far enough. Could be a few things IF the that group slides freely inside the upper, which you stated it did. Then it's gas or buffer/spring related. In rare instances under powered ammo. I know of rifles that run great with a few ammo brands and then you go and switch to brand Y and it starts doing the things you have.

I would try another spring/buffer and other types of ammo.
I have seen this with some ammo made in the last 2 years for some reason.

quote:

Originally posted by CAS II:
Da Man, go screw yourself.

Just as I thought....... a clueless moron!

Look at those photos and look where the bolt ended up on top of the case. Doesn't that give you a clue as to what's going on?!!!

when you have that failure to feed if you pull the bolt back and let it slam forward does it complete the feeding of the cartridge ? If so it would indicate that for some reason you are not getting enough gas pressure to bring the bolt all the way back properly. That would also explain the inconsistent ejection pattern.

quote:

Originally posted by plainsman456:
I would try another spring/buffer and other types of ammo.
I have seen this with some ammo made in the last 2 years for some reason.

I agree with trying another spring/buffer. But I don't think there is a problem with the ammo or mags (both types of factory ammo mentioned provide good operation).

Seeing as how this upper was designed for use with relatively heavy bullets, might one try a heavier load? Seems to me if a standard load is failing to bring the bolt fully rearward a heavy load might be the ticket. Not too dissimilar to recoil operated guns in that when set for heavy loads a light target load fails to work the bolt fully.

Then again I could just be smokin' crack.

quote:

Originally posted by drewhenrytnt:
Seeing as how this upper was designed for use with relatively heavy bullets, might one try a heavier load? Seems to me if a standard load is failing to bring the bolt fully rearward a heavy load might be the ticket. Not too dissimilar to recoil operated guns in that when set for heavy loads a light target load fails to work the bolt fully.

Then again I could just be smokin' crack.

Drew, the two factory loads mentioned should provide adequate gas port pressure. The Winchester 55 gr. (Q3131) is almost an exact twin to the old M-193 military round.

What this guy is experiencing is classic "short recoil" but I'd rule out the commercial ammo he's using as the cause.

quote:

Originally posted by DaMan:

quote:

Originally posted by drewhenrytnt:
Seeing as how this upper was designed for use with relatively heavy bullets, might one try a heavier load? Seems to me if a standard load is failing to bring the bolt fully rearward a heavy load might be the ticket. Not too dissimilar to recoil operated guns in that when set for heavy loads a light target load fails to work the bolt fully.

Then again I could just be smokin' crack.

Drew, the two factory loads mentioned should provide adequate gas port pressure. The Winchester 55 gr. (Q3131) is almost an exact twin to the old M-193 military round.

What this guy is experiencing is classic "short recoil" but I'd rule out the commercial ammo he's using as the cause.

The upper has nothing to do with the bullet weight...it's the lower that contains the buffer and buffer spring. Maybe to a little degree the size of the gas port hole has some to do with how the rifle functions, but it's generally more tuned to different calibers then loads. Notice the M16 was never designed with an adjustable gas valve. Now the size and location of the hole has a lot to do with which barrel length is used.

quote:

Originally posted by drewhenrytnt:
Not too dissimilar to recoil operated guns in that when set for heavy loads a light target load fails to work the bolt fully.

No, Drew. "Gas impingment systems" rely SOLEY on proper gas pressures delivered at the barrel gas port and delivered to operating parts.

But ANY factory loads for this caliber will NOT cause a problem.

The reason most factory loads work in most all 5.56 rifles is that all the rifles are over gassed to insure functioning in all conditions with all ammo. The cost of this is unnecessary beating of the action. I have gas valves on almost all my AR's and they work perfect with the gas cut back just enough to still insure full cycling. The carrier weight that David Tubbs came out with was because like I mentioned most AR's are over gassed and beat the action. His weigh slows the bolt/carrier groups timing to which insures all the gas pressure is gone from the chamber and bore.

I consulted my local AR15 Celebrities and smiths. I showed them these posts and pictures. They have all stated the most likely culprit is bad gas rings.

That being said, if you replace the gas rings and it solves the problem, I will cover the cost of the rings. If it does not solve the problem I will refund your money plus the cost of rings and shipping the upper back to me.

Andy

Gas rings are easy to check take the bolt and carrier out of the gun. Extend the bolt into the forward position. lightly stand the bolt/carier up right on a table bolt head on the table let go of the carrier.

If the carrier rides down over the bolt the gas rings need to replaced if the carrier is held up the gas rings are still good.

If the carrier dropped we would the replace gas rings as a matter of course.

That said I have seen carriers drop right now and the gun still functioned. It is just one thing to check to try and find the problem.

definitely looks like a gas ring prolem. Check the cut in the three rings not being alined and causing this lack of push by gases bleeding away too easily, sometimes it is enough to cure this FTF.

so what did you find out?