Ive posted about this before, but finally got back to the range today to retest it out.

ive got a M16a2, ive turned it into a M4 basically....i have a 11.5 BCM upper i use with it suppressed...works great...never 1 malfunction!

i picked up a 14.5 upper off a forum a couple of months ago...it isnt working well....thought it was the buffer...nope, thought it was the mag, nope

in semi auto it functions 100%, but wont hold the bolt open on the last round------in full auto it often only gives doubles and jams up...sometimes it doesn't grab a round, sometimes it stove pipes a round....ive come to the conclusion its not getting enough gas as the majority of the time it doesnt stay open on the last round

its a Colt M16a2 w/a Colt 14"upper made 5/15...it appeared to be brand new when i got it....

could the gas block be out of alignment? is this something Colt would warranty?

one other odd thing about my m16a2 in general...it doesnt like you putting a full mag into it w/o the bolt open...with my BCM upper it will go in, but you need to smack it...with the 14" upper it wont go in no matter what....an empty mag goes right in, but load it to 30 rounds and it wont budge...not sure if this could be part of the above problem or not? just mentioning it

any opinions before i take the upper in?

ammo: Wolf Gold--works flawless in every AR/M16 i own
Buffer: H and H2

saw some info about the BCG being over parkerized and needing to be worn in....this bolt is heavily black....i can swap my BCM BCG next time i go to the range...also try it on my AR lowers

Have you used a BCG that is  known to function in FA ? You stated you changed buffers.  But did you use a standard one ?

Sounds like it is under gassed. Check for a loose, or leaking bolt carrier key. Try some hotter ammunition. You might need to use a lighter buffer with that upper.

I have no clue about the loading issue.

i used a H and a H2 buffer...no change when switching to either....it didnt get worse when i used a H2

i thought Wolf gold was pretty decent stuff---it has been flawless in everything i own...not the junk steel Wolf----Wolf Gold is brass cased and i thought fairly powerful?

Ive got my BCG in my hand...the gas key is solid and i blew hard into it and it wasnt leaking...not sure if thats the best test? but it wasnt blowing air anywhere

its a Colt...says C right on it....

suggest my next test to swap BCG with my Bravo Company?...all the AR's i own have FA BCG's, so i can swap with any

its a Socom upper and i hate to think its the BCG.....if it is i wonder if Colt would warranty it...it wasnt cheap and i assumed the Colt Socom would be the best and designed for blasting away w/o issues

You were going the wrong way with the buffers. Try a standard one. Also a standard recoil spring. It does indeed sound like your under gassed.  With the failure to lock back and the failure to feed.  You might want to be sure it's over lubed up till it gets broken in some, it can't hurt.

Probably the best thing I did to my M16 was to install the A5 receiver extension and buffer. Not that will cure this problem.  But at least I didn't have to play musical buffers when changing uppers.  It worked with everything from a 10.5 to a 20".

Try some real NATO Cross ammo too.  What your using is loaded closer to .223 pressures.

I started out with the A5 extension and buffer on my M16A2 as well.  I switch from a 16" Colt SOCOM upper to a PSA CHF 10.5" (my "mag dump" upper) to a BCM 11.5" without a hiccup.  I'm running Lake City M193, but I wouldn't hesitate to run Wolf Gold with it.  In fact, I may pick up a case just to see.  The only time I've ever had any sort of malfunction with it is when I removed the can from the BCM and forgot to switch the Gemtech carrier back to "unsuppressed."  I have all buffer weights for it just in case, and the system is so elastic that I've tried everything from the A-0 to the A-4 without malfunction.  Just changes the cyclic rate a bit.  I finally just stuck the A-2 back in and quit messing with it.
The only down side is that now I want one on all my other (non-MG) lowers too.

i talked to my gun dealer today about it..since its 2015 manufacture he said Colt would most likely warranty it if it turns out to be the bolt...he also said he has seen over sized Colt bolts

only 300 rounds through it...so it could just need more lube and break in....next time i go to the range ill bring all my AR's and my M16 with both uppers...ill try swapping it on my AR and see if it holds the bolt open...then ill put it on my M16 and swap BCG's and see if it runs....figure out which part is the problem....my 11.5" runs flawless...so i dont think its the buffer or spring......a 14.5" should run the same you'd think.......the BCG is heavily parkerized....so maybe its just break in needed....i do use decent lube, but not heavy...ill try heavy next time

im just glad to hear if worse comes to worse i can hand it off to Colt....i bought it specifically because it was 100% Colt....i dont want to start tossing in a BCM BCG to get it to run

thanks for all the idea's!

The fact that when you used a heavier buffer the problem increased. Is telling you something.  A standard buffer might well be the fix your looking for.

i dont think i said the problem increased with the H2 buffer...i saw no difference...went back and forth a couple of times

i did have less jams on the first mag(maybe none) and after 120 rounds the problem did seem to be worse though....not sure if this shows a lubrication issue?  

2nd mag for sure had issues...but the first mag might have functioned 100% or close to it

Yea my mistake I read didn't as did.

you are forgiven

Finally got back to the range today to do some more testing...took my sons buffer and spring out of his Colt 6920, tossed them into mind and it ran flawless...so problem solved

so im going to buy a H buffer...

one thing i noticed about the spring...his was shorter than mine...so ill grab a new spring also...i wish i would have just tested the buffer alone, but too late now....my spring is a BCM standard spring....id like to get a colt brand standard spring, but cant find one for sale....go to Colt and they push you to Brownells...so i guess ill just grab one from them....

Nice to solve a problem

hey found genuine Colt at Midway usa....funny Colt sends you to Brownells which doesnt carry the colt brand from what i can tell on these parts