Earlier today I got my new barrel installed onto a new to me upper.  The upper is a Colt M4 flattop, used in good condition w/ feedramps and marked rail.  Barrel is a heavy Colt M4 14.5 inch, AKA the SOCOM barrel, and was new.  Got it installed with not much issue, key was rubbing on the gas tube just a little but i cranked down the nut a hair more and now the key slides over it like butter.  Decided to test fire it.  Took out 80rnds of S&B .223 brass case 55grn.  A friend was shooting it at the time, and after about 55rnds total, he had a stoppage.  It was probably the 6-8th round in the magazine.

I took the rifle from him to see exactly what the problem was, and it appeared that the bolt had overridden the case, and jammed it at an angle (upwards, maybe 50 deg. or so) when trying to feed it into the chamber.   We cleared it and disposed of the round, and finished the 80rnds I brought with no problems.

The magazine was an excellent condition Okay 30rnd with green follower.  I don't know the history of it, it was purchased used.  Many will give the S&B flak but that rifle has fired 1056 rounds before putting the new upper/barrel on it, many of that was S&B and I've had no problems at all, other than needing a stronger extractor spring.  The old barrel was a standard profile Colt 14.5" M4.

Since I've not used the magazine before, I'm hoping that was the problem.  The bolt locked back on all 4 magazines I was using just fine.  I know it's a little hard to diagnose a problem with just 1 malfunction with 1 type of ammo but I figured I might at least get some ideas.  I plan on shooting it again soon with either some type of M193 or Win. white box.

it is a common dictum in the military that "90% of all reliability issues with the M16 are magazine related"  i have found this to be mostly true if you are using a properly assembled and maintained rifle built of top tier parts.

Is the short stroke test where you hold the bolt hold-open and fire a round to see if it locks the bolt to the rear?

Quoted: Is the short stroke test where you hold the bolt hold-open and fire a round to see if it locks the bolt to the rear?

Single round in the mag, the round charged and fired, then the bolt locking back on the bolt hold open (mag follower appling the pressure only).

Quoted: Quoted: Is the short stroke test where you hold the bolt hold-open and fire a round to see if it locks the bolt to the rear? yes

OK, my n00b-ness will prevail here... but doesn't that sound a bit dangerous? Maybe if one of you guys did an instructional video *Hint!!* on how to do it.... Like hell if I'm going to give that a try w/o any knowledge of what to do heh.

Quoted: Quoted: Quoted: Is the short stroke test where you hold the bolt hold-open and fire a round to see if it locks the bolt to the rear? yes OK, my n00b-ness will prevail here... but doesn't that sound a bit dangerous? Maybe if one of you guys did an instructional video *Hint!!* on how to do it.... Like hell if I'm going to give that a try w/o any knowledge of what to do heh.

No, instead of loading all 30 rounds in a mag, you only load one.  When the single round is loaded into the rifle, the mag is empty, and what you are testing is if the B/C moves all the way back in order for the last shot hold open bolt catch to catch the bolt (hold it open, hence checking to see if the B/C is fully cycling all the way back).

1 malfunction in the first 80 rounds fired.......

Does not constitute a problem IMO, most "break-in" malfunctions occur in the first 200 rounds or so.

Now if it starts doing this on a regular basis, I'd be concerned.

Mike