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.

Just wondering, what size gas port is on the LMT 10.5" barrel

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.  

VaDinger,
What bcg do you use in your LMT?
Thanks,
Brent

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.

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?

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.

I've had nothing but good luck with the 10.3" short gas upper I bought from CMMGinc.  It's been 100% reliable for well over 500 rounds.  No problems NO malfunctions.  I run it on my registered fullauto and it did several full 30 round mag dumps without a hitch.  I've been very pleased with this upper so far.  Here's a picture of the setup.



Andrew

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.

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

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?

tagged for working project

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.

Which ever you choose, I'd make sure it can take the higher blast heat internally. I.E., built with Iconel and Stainless Steel, no aluminum which can warp and possibly be trashed in no time. Something like SWR's Specwar-1 is where I'd start. Just my thoughts.

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.......

Please correct me if I'm wrong, but doesn't a FA bolt carrier, in a semi gun, in the eyes of the nice ATF, an M16 make? I've heard it only takes one (1) auto part for them to nail you to the two bunk wall for creating an unregistered weapon...........If I were on a jury, I wouldn't convict you, but, the prosecutors (and most lawyers in general) try to find the most ignorant people, not experts as jurors so they can "shape" their minds to suit their own agendas.........
I agree that the extra weight might make cycling issues easier, but, is this good advise to be giving? Legal thoughts?
When it's said and done, you can't be too prepared when the SHTF.

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.

Also try the Bolt Enhancement Upgrade. You'll get longer bolt retentaion on the round and more time to eject.

SBR's are a bitch to get the timing corrct on so pay attention to your adjustments and record them so you know when oyou find the "Secret Sayue".You may want to contact folks like Deny at Denny's guns or mark LaRue at larue tactical.com for help. They do a lot of building of the SBR platform.

Personally...I hate 'em! I just don't want to to screw with them an I don't need the 10.5" length.

Tack

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 ...

Same for me when I went from 20" to 14.5" Bush HB and CAR stock. Semi was fine. Major bolt bounce and/or short stroke on full auto. I tried everything, new extractors, spring clipping, carriers. All it took was a heavier buffer. Simple. Do go with the O-ring mod as well. I was getting failure to extract AND trying to feed another round on top of that, all with a 14.5".
If you want reliable 10.5" uppers, I hear the LMT's can't be beat, but I'd still use a H or H2 buffer. Done deal. He'll probably want a Noveske flash hider with a 10.5" to keep his hearing though. Another $125.

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...............

For what's it worth, I have bought 2 uppers from M&A Parts. 1 is 10 inch the other 11 1/2 inch, and both of them run all day long.
There is nothing special except that they got the gas hole the right size. No funny pig tails, no over sizing the gas hole, just darn good stuff form M&A.
Now talk about 7 inchers,,,,,I have never seen one that will go fact and empty a 30 rd mag without hiccuping at least once.
If anyone know a good builder of them 7inchers, please let me know....
good luck, and keep your powder dry :)

I had the same problem. The carrier isn't coming back far enough to pick up another round but, far enough to eject, open up the gas port going to the gas tube.
How exactly do you open up the port? With a drill.

choose a drill bit that is just slighty larger than the current gas port and go slow, then test.

AR10 buffer spring fixed all my 10.5" M16's issues.

Okay, I've followed this one for a while and finally decided to try a 10.5 upper on my RR.

I took some of your advice and got a LMT 10.3" upper with a LMT BCG. I added a 1-piece gas ring to the BCG and a H2 buffer in the carbine length lower.

This thing short strokes with all the ammo I have tried in it. M855 seems to work the best and will cycle the gun, but it won't lock open unless I'm running the suppressor. Most other ammo won't run at all without the suppressor, it'll kick the spent case out and close without picking up another. I had a wolf spring in it at first and it would short stroke with the M855. After changing the spring back to a normal one it seems to barely run with the M855. I thought it might loosen up after a while but 1000rnds later it seems to be worse if anything.

I haven't heard of anyone ever having problems with the LMT uppers. Is it possible that this thing needs the gas port reamed out a bit? I did take the gas block off and chop it so I could mount a DD rail over the top it. I don't know what I could have screwed up there though. I've thought about trying a different buffer, but it seems to me like something must me wrong or it would be working fine with the H2 everyone else seems to use. I think I've checked all of the obvious stuff like the gas key, gas tube fit, etc. I'd appreciate any ideas you guys might have.

ETA: Never mind. It seems to have loosened up a bit now. Another 500rnds and a good cleaning seems to have sorted it out. It still doesn't like the silver bear but I think it's probably about the best compromise I'm going to get between unsuppressed and suppressed use. I've also noticed that it's a lot more sensitive to buffers than I would have thought. H works fine without the suppressor, H2 is fast suppressed (but no bolt bounce) and H3 is probably ideal with the suppressor. I still haven't tried the H with the suppressor, but I'm not in any hurry as it's running really fast with the H2.

Now for a new one: Has anyone else noticed copper buildup on the brake or suppressor with one of these shorties? I've got a PWS brake that fits the YHM can and it's coated with copper now.  I have to scrape the copper off of the brake every so often or the can gets difficult to install/remove.

Time Warp Thread.