Originally Posted By Tweak: I wouldn't put too much stock in the actual barrel length numbers when you get down under an inch. If the barrel is threaded (the 0.5" diameter) immediately forward of the FSB the barrel is right at 10" some call it a 10.5" tho, others call it 10.25"

Thanks for the reply. Here are the two examples I was going off of:

LMT 10.5" upper receiver (from an EE ad):



Colt 10" SBR (from a JB Arms ad - strangely enough, the ad is for their 11.5" 6933s):



The Colt definitely fits your description of having the barrel threaded right past the FSB - don't think they could get it any shorter than that!

Dave

I have a police issued 10" bushmaster that I have put a full auto m16 lower on and it works great. Never had a problem.

I have had zero problems with my LMT/Noveske 10.5" after close to five thousand rounds. I would not get hung up on the 10.5" vs. 11.5" barrel debates. In my experience that 1" of extra barrel is not a cure all and an improperly maintained & set-up 11.5" will have the same exact problems as a 10.5" set up similarly. You will read over and over guys recommending 11.5”’s like it solves all the problems, but that’s just not the case. I think they are just reposting things they have read in the past and the original author had no idea what he was talking about in the first place. It’s a vicious cycle of bad info.

In my opinion keeping a 10.5”-11.5” AR reliable is just like owning a stone reliable 1911. It takes a dedicated owner/user who is willing to take the time for proper set-up, maintenance, preventative maintenance, and of course near religious dedication to cleaning & lubrication.

My personal recommendations for a 10.5”- 11.5” AR:

(1.) Wolf HD extractor spring – change them out every 4,000 rounds.
(2.) Adco Crane o-ring or D-Fender – Inspect during every cleaning and change out if it shows any wear.
(3.) 1-piece gas rings – I do not personally run this set-up but others that I trust swear by it.
(4.) Extractor – Inspect every time you clean, if it shows signs of wear replace it.
(5.) Buffer – run an “H” buffer at the very least. I have had great luck with LMT “H2” buffers.
(6.) Cleaning & lubrication – SBR AR’s require more dedication to cleaning & lubrication. You will most likely not be able to get away with putting it off like you would with a 16” weapon. The SBR is more finicky and it will bite you in the ass at some point down the road. Keep it clean and well lubricated. Pay particular attention to lubrication on the high friction areas on your AR. **Do not worry about the "Over Lubricated" myth*** Pour it on and simply wipe off the excess after the weapon is reassembled.
(7.) USGI mags w/ MagPul followers or HK. These help with any AR, so why take a chance?
(8.) Ammo – factory ammo that has proven itself reliable in your weapon.

Originally Posted By x-boxcommando: VaDinger, What bcg do you use in your LMT? Thanks, Brent

I run standard LMT bolts with Wolf HD extractor springs/Adco CRANE O-rings & standard LMT M16 full-auto bolt carriers.

Gas problem. Try changing buffer assembly first. There is not enough barrel gas back pressure to retract bolt. Allow the bolt to retract easier, but try not cutting coils first. Buffer springs usually do it Also the gas tube must have the correct length and tappered fit to the bolt carrier, or gas escapes before filling in carrier bolt gas collection tube. You could end up with a dirtier gun.

Originally Posted By x-boxcommando: Originally Posted By Va_Dinger: Originally Posted By x-boxcommando: VaDinger, What bcg do you use in your LMT? Thanks, Brent I run standard LMT bolts with Wolf HD extractor springs/Adco CRANE O-rings & standard LMT M16 full-auto bolt carriers. Please excuse a dumb question, whats the difference between a semi and f/a bolt carrier?Stronger? Why no f/a bolt as well?

The difference is that a semiauto carrier will not run a fullauto gun. The bolt is the same for full or semi auto, only the carrier itself is the difference since that is what trips the auto sear.

Here's a good picture of the 3 different style bolt carriers.

Originally Posted By rsilvers: People should use full auto carriers all of the time. They are the correct weight. A semi-auto carrier has less mass.

Very true, the extra weight helps with recaoil. I run full auto carriers in all my guns for that reason.

so if you a heavy 9mm buffer or full size a2 rifle buffer will this help a 10.5 upper?

Originally Posted By 321Bang: A police friend of mine just purchased a 10.5 A2 upper for his issue M16. The 20 in upper runs fine and the 10.5 fires fine and will eject like it should but it will not pick up another round from the magazine. It is as if it is either cycling so fast that the mag doesn't have time to push another round up, or the carrier isn't coming back far enough to pick up another round but, far enough to eject. He is wanting to clip a couple of coils off of the action spring. My solution is to open up the gas port going to the gas tube. What do you guys think? How exactly do you open up the port? Who is right? To clip or not to clip is the question. I don't think that clipping is the answer since it runs fine with the 20 in. Oh and by the way his lower is using the collapsible stock and we have tried several mags. Thanks...321

this was the thread or topic I first came to post with. SBR or 11.5 RR upper that would FTFeed and FTXtract. I solved the problem with serious cleaning and more powerful mil spec loads. in 5.56 mm, such as M855 62 grain. It didn't fail with 55 grain ammo in semi auto though, but would in 3 shot and full.

After several years after changing my perfectly working 20" AR-15 Colt Reg. Rec. to a 14.5" BM with CAR stock, while working fine in semi, I was having problems on full auto.... tried the 2 spring clip idea, slightly opening up the gas port, changing bolts, extractors, springs, all it took was for someone who "knew" to change out my plain old car buffer with what he called a "2 piece" one as well. I suppose this is just a heavier buffer. Then he proceeded to dump about 4 30rd mags with no jams like you described. My bargain ($1750 in 1998 MG) finally made the music I was seeking. I was getting the failure to extract-but trying to feed, light primer strike issues no matter what. I guess "BOLT BOUNCE" is what I was encountering. IF I ever get a 10.5", it will be an LMT for sure.......

Colt has been shipping all Ar15's (yes even Match Targets) with the full auto carriers for a few years now. There is a copy of a letter from the ATF to Colt floating around here somewhere on this exact same matter. It is ok to run the full carrier.

Originally Posted By AK_Mike: <center><table width=85% border=0><tr><td width=100% class=textQuote><hr height=1px color=black noshade>Originally Posted By pazzo: I know that GemTech does not recommend suppressors on this short barrel since they say it won't stabilize the bullet enough to prevent baffle strikes. But I would think 1/7 twist combined with 55gr. projectiles would get enough spin to make it out of the suppressor without baffle strikes.<hr height=1px color=black noshade> You misunderstand. Gemtech does not recommend it because on a short barrel the tremendous gas blast destabilizes the bullet too much, causing baffle strikes (SNIP)....

Actually it was also explained to me by Gemtech as an issue with not enough barrel to stabilize the bullet. I know I did not misunderstand there rep because he gave me a great example.

He compared the bullet leaving the barrel to a fighter jet leaving the deck of a carrier. After the catapult gets it in the air -- the jet will wobble for a while before it stabilizes ...

Originally Posted By ar15inmn: Colt has been shipping all Ar15's (yes even Match Targets) with the full auto carriers for a few years now. There is a copy of a letter from the ATF to Colt floating around here somewhere on this exact same matter. It is ok to run the full carrier.

Nice to know, that's all I'll buy from now on...............