I had the same problems. The gun would fire but not pick up a round from the mag. I could cycle it by hand though and everything pointed to short stroke. I know this sounds way way off but its easier than removing the front site. Before you start drilling holes out, look at the feed ramps, are they exactly like a M4. If not a Dremel tool will fix that.You might want to slightly widen and deepen the feed ramps. BTW just visual inspection of the feed ramps looked fine on my upper.

Send it to me and I can get it to work.  Have done it many times before.  with the short barrel you loose gas pressure thus not getting enough back to the carrier thus it short strokes.  My 11.5 was finicky once too, same principle.

How about an adjustable gas tube???

I would like to save to for further reference when I aquire a shorty

last weekend i looked at one with the same problem, the fix was that one in a thousand chance that all three gas ring notches lined up, i took the bolt out and rotated the rings and it was back to normal. im sure you allready tried other mags?or if there is a stick on buffer on the buffer ,take it off,

Gentlemen,
As always you are a wealth of great information. May I add another question that's not very far of topic? Do the factory Colt Commandos have this same problem and do they need any tweaking to make them run reliably? Our PD is deciding between the 14.5" and the Commando but it seems like most of the dealers are trying to talk us out of the shorter barrel. They claim reliability issues...

Any input? Maybe this should be a new thread.

Another gas ring case.

Amazing how many times I have heard/seen the gas rings being a problem...

I have shot a few 10.5" uppers using adjustable gas tubes and they did run well.  However, I received a rather bad burn from grabbing the part the adjustable part that sticks above the handguard.

I know it was stupid of me, but I was just grabbing the handguard to sit it down to cool.

TS

I've never had a gas ring problem with a 20" H-bar.  Whenever rebarreling comes around is when they get changed. [peep]

Good got you.  The vast majority of people do not need a new barrel and hardly ever/never change their rings.

Sounds like the LMT 10.5 inch uppers run pretty well. I wonder what it is in particular about them that makes them more reliable?

My guess is they found the gas system size that worked best then reproduced it with the TIGHTEST tolerances.  Most importantly a supertight, near-leakproof gasblock.  (That or just some LMT fairy dust.)  Either way they do something many others can't--run out of the box...(suppressed too)

I owned a 10" barreled upper for awhile. It ran just fine. I have since switched to the 11.5". The 203 mounts better. No matter what barrel you use, the rifle will need the same volume of gas to operate. The gas is only applied to the action for the length of time that the bullet is between the gas port and the muzzle. This is the duration of the gas cycle. The amount of gas is determined by the length of barrel from the gas port forward to the muzzle. The duration starts as soon as the base of the bullet passes the gas port, and ends when the bullet exits the barrel. On a standard 20" barrel you have right at 7" of duration. On the shorter class 3 barrels (10", 11.5", 14")you have a shorter duration. My 11.5" has 3.5" of duration. this will require a larger gas port in the top of the barrel. The 10" barrel will require a slightly larger port due to it's even shorter duration. Open up the port slightly reassemble the rifle and try one or 2 shots. continue this until it operates smoothly.
Where is the department armourer? this is his responsability.
Actually if your L.O.E. buddy doesn't want to become familiar enough with his weapon fix it himself, I would question if he should even have such a weapon.  

If your gas hole is to large it will cycle violently, and upset the timing, to small and it will not fully cycle, make sure the barrel was'nt a cut down 14.5, 16 or 20 inch barrell.  With correct gas port size it will work.
Fran

IMO, If considering a barrel in the 10 - 11.5 range, be sure to consider the tradeoff in lethality, as well as reduced reliability and your possible loss of hearing from the noise. If you HAVE to have a shorty, at least know the score.

Wes,  do you have that LMT 10.5 upper left?  How much?

FYI, the MGI adjustable gas-tube system, with the RateReducing/RecoilReducing Buffer, and the D-Fender extractor D-Ring will make most, if not all, short barrelled AR15/M16's run reliably.

Here is a recent testimonial from one happy user.
"Dear Mack, all I can say is WOW! I put your buffer and D-Fender in my short barreled M-16 and this is the first time that it has ever worked correctly both full auto and semi with no hang ups...... Thanks for a Great Product!
Sincerely yours,
CF"(from Ohio)

I am the MGI factory rep.
I can answer your questions or take orders by email.
[email protected]
Adj. Gas tube - $59.95
RRB Buffer - $150.00
D-Fender - $12.95
Plus shipping.

What kind of suppressor are you guys running on the LMT 10.5" upper?  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.

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.

You misunderstand.  Gemtech does not recommend it because on a short barrel the tremendous gas blast destabilizes the bullet too much, causing baffle strikes.  Twist and projectile weight have nothing to do with it.  All bullets, as far as I know, wobble a bit when exiting the barrel, even long ones.  It's the gas (from the propellant) behind it that destabilizes it, more or less depending on bullet shape/design and muzzle device.  The shorter barrel produces a lot more gas blasting behind the bullet than the longer barrel so the bullet wobbles more.

Originally Posted By AK_Mike: 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. You misunderstand.  Gemtech does not recommend it because on a short barrel the tremendous gas blast destabilizes the bullet too much, causing baffle strikes.  Twist and projectile weight have nothing to do with it.  All bullets, as far as I know, wobble a bit when exiting the barrel, even long ones.  It's the gas (from the propellant) behind it that destabilizes it, more or less depending on bullet shape/design and muzzle device.  The shorter barrel produces a lot more gas blasting behind the bullet than the longer barrel so the bullet wobbles more.

So, can someone answer the question?  What supressors are yall using with 10.5s ?

Thanks for all the good 411. My 10.5 is now running well after adding 1.5 oz. to the buffer. I am going to run 4 or 500 rounds through it Thursday I post how it went. Fingers crossed.
I tried it out ...... I fired 30 rounds semi first with no problems. Went to auto it fired 3 rounds and quit with an unfired shell in the chamber. Auto again, one shot fired, unfired shell in chamber. Tried again, two shots fired, bolt returned halfway back with bolt face resting about midway on next round to be loaded. The shell was half way out of the magazine on its way into the chamber. ???????
When this lower is on a 20 inch upper we have 2000 rounds through it without one miss fire.
I guess next I will try the 20 inch upper with the CAR stock and see if it runs ??????????????

tag.  just starting down the SBR road myself

Thread on converting standard car buffer to the heavy car buffer for the 10.5 barrel MG

I've been going through old posts on some of the advantages of using an H-buffer. Given the number of CAR buffers that I would like to convert, the least desirable option is to buy all new H-buffers. So I was wondering if anybody had successfully converted a normal CAR buffer to an H-buffer by either adding or changing the type/number of weights in the buffer body - and if so, what components were used.
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Cylindrical tungsten fishing weights.
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Hmm, what size? I've been looking, and it looks like these are the best candidate:
http://www.cabelas.com/information/Fishing/ExcaliburTungstenWeights0017580.html
http://www.lakeforktackle.com/weights.htm
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I'm going to take a trip out to Galyans and WalMart to see what they have. Looks like the weights in the original tube are 0.54" in diameter (with a inner buffer diameter of 0.57") and there's about 2.2" of overall to work with in the buffer tube.
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I have done it by replacing the cylinders with 50 cal lead balls that I smash with a vice until they are the right diameter to fit in the buffer. It is just over 110 grams when I do that.
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After a day of running around to different sporting goods stores, I'm happy to report that the project is a success. I ended up using 3/4 ounce Excalibur Tungsten Barrel Weights which I found at Galyans. I picked the 3/4 ounce weight over the 1 ounce weight because dimensionally, three of the 3/4 ounce weights would fit inside a CAR buffer body. The leftover space was then filled in with #8 shot from a cannibalized shotgun shell.
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Total weight after the transplant was 4.2 ounces which is a little heavier than a 3.8 ounce H-buffer. Compared with lead, the tungsten weights aren't cheap - I paid $3.99 for two weights - so total cost to retrofit each buffer was $6 plus whatever a shotgun shell cost.
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I might have to try IDHunt's idea as National Bullet is down the street and they have .530 diameter lead balls at 25 for $8. If you don't mind me asking, how many lead balls did you end up using per buffer?
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I don't think that lead would be a very good idea. It is just going to peen and then the buffer will jam up and no longer be anti bounce.
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Correct, lead will not work in a full auto buffer, after firing it gets mashed in and will not move and is extremely hard to get out. Stick with the tungsten and leave a little play so the anti bounce feature can work, do not fill the remaining space with lead shot.

Hey all, I have an Essential Arms SWD conversion and when i first got it transferred, it wouldnt run for crap with the 10.5" bbl and CAR stock.  It would, however, run fine with the fixed stock on, but didnt look nearly as neat :).  It also would not run with the 20" bbl with the CAR stock, and looked goofy that way too.  I fixed my prob with the DPMS 2 piece counterweight buffer, though I did have to take it apart and make sure that the two parts moved freely, it was machined too close when i got it.  I havent had a malfunction since.  Most of the problems I encountered were of the short-stroking variety, there would be a live round in the chamber with a superficial tap on the primer and the hammer would be down.

W

Here is some good history on the Colt 10" Commando rifle. http://www.isayeret.com/weapons/assault/car15/car15sawn.htm

Hello, I read about your plight on the AR15 boards and thought I should pass along my experience of the 10.5 barrel blues.

I have an M-16 with a 10.5" bbl. that would jam about every 50 rnds or so with GI ammo and more often with commercial ammo. After going thru all the recommended fixes, ie, Pigtail, Fat boy gas tube, opening up the gas port, et al.
I just tried a full legth fixed stock recoil spring and a heavy 2 piece Colt Commando buffer. I have not has a jam since I did it. I have all Colt parts, but I found that on my Bushmaster shorty I couldn't use the full stock spring in the buffer tube by Bushmaster but used the spring cut down 1.5-2 coils worked fine.
My recommendation, try this before you go taking off the front sight/gas port base.
The Colt 2-piece buffer costs about $55 from SAW in Chandler AZ.

I was one of the developers of the Arms-Tech Compact M-16 system, a 9.5"bbl gas-trap chambered systemand have fired a lot of 5,56mm ammo in the M-16 weapons systems. We got 14.5" bbl. velocities out of our 9.5"bbl. and less chamber/lead erosion.
The most common problem is the weapon firing too fast for the carrrier to go back into battey berfore the next round is loaded in the chamber. Bolt-bouce and all that stuff is a myth. All you need to do is slow it down.

Just my observations thougth I would pass along to you...

Regards, Curt
Capital Ordnance, LLC
480-941-8554 Store Tues-Sat
FFL/SOT 07 NFA mfg.

my m17 [ea] came with an 11.5 223 and 10.5 9mm uppers and a collapsable stock

9mm rock solid

223 was firing one or 2 then bolt closed on the next round and light firing pin mark on the primer - had heavy buffer, etc - tried several different fixes but the one that worked was aac csmkII mechanical buffer - cured the bolt bounce - everything works fine now

Just saw you have the same problem I did.I tried everything including gas port changes. What worked for me is a cyclic rate reducer from Advanced Armament Corp.She will be running great in no time!I have a 07 manufacturers licence (NFA).You can e-mail me at [email protected] the way I did pick up a Arms Tech 9.5" upper.The one with gain twist polygonal rifling.They claim same velocities out of their 9.5 as the 14.5" standard M-4s.Going to the range with my Chrony tomorrow to find out.Will report......................

Just an observation to the problem.

If you don't have enough barrel after the gas port, why not more the gas port back, toward the receiver.  Put the port in the 7" barrel location and use a shaved front sight, a mini Dissy so to speak.  Use a smaller port to overcome the higher pressure of a port so far back but you have more barrel afterwards.

Just a thought.  I'm dying for a SBR build and have been watching this thread with an interest.

Brad

I just wanted to chip in,,,, I recently bought an early run lmt unmarked 10.5 upper
and when I first put it on my sbr lower, it shortstroked every 3 or 4 shots,,,,,
I made sure everything was clean and correct on the upper, then I put a h buffer and spring in the lower and bang,,, there she goes,,, perfect every time......

so guys with problems, don't give up,,,, I put 500 rnds down her yesterday,,, and absolutely had a blast!!

I run a 6.5 w/ standard pistol tube...no issues on semi or FA.

Bought a LMT 10.5, no issues either...popped the pins, threw it on and runs like a champ.

Originally Posted By greenmountainpatriot: I run a 6.5 w/ standard pistol tube...no issues on semi or FA. Bought a LMT 10.5, no issues either...popped the pins, threw it on and runs like a champ.

Colt upper / 10inches plus   / m16 bolt carrier   / xm193 runs great  / 1 piece gas rings /  o-ring extractor / hk mags/  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The M16 platform is sensitive when it comes to the gas pulse. I have one running in 223 that has a 6.5 inch barrel and it has the pigtail tube.
The distance from the port to the muzzle is the critical area as this dictates the time curve that you have pressure available.
A slightly larger hole can help but dont cut the spring. I would definately use the pigtail; tube from olympic. This will foll the gun into thinking it has a full length barrel.
I manufacture the Thunder Sabre carbine which is chambered for the 502 (50 cal) cartridge and I also offer the  12.7 Thunder Boss  CTW which is the same 50 cal cartridge but the gun has a 7.5 inch barrel and a short tactical stock.
Getting the short barreled beast to run right took some late night oil and some outside the box thinking but when it was done it was sweet.
My Thunder Boss uppers are available now if anyone is interested.
At any rate the shorter barreled 223 guns can cause a trifle of troubles to get them to run right but once you get them dialed in they are quite nice.

Update ............ A year ago I went to the heavy buffer with my 10.5. That fixed all of my problems. It runs so well I bought a Beta Mag. I can dump all 100 rounds with out a jam or misfire. I do melt gas tubes though. I'm working on that one .

RatsWithKnives

I have a Colt 10.5 upper that I sent to Mr. Greg Leaf at the M16 Clinic, which would have FTF, FTE and other assorted anomalies every other shot. The gun was a M16 A1 turned into a Commando type weapon by the armorer at Las Vegas SWaT. I guess they gave up on it too.
Well he essentially blueprinted the thing, and found not one but two overbored gas ports, so he drilled a correct one. BUt he also sent me a Wolff Extra Power Spring AND a 9mm buffer, which is heavier than the ones for the 5.56 carbines including the H2 for the M4.
Now the 10.5 only stops firing when I want it to!!!!
BTW, I also sent him a BM M4 upper, which he also blueprinted, and works perfect with the above-mentioned spring & buffer.
Greg is now selling a 10.5 in. custom upper called the Viper which is getting rave reviews from the sandbox.

Good luck with your shorties.

Jorge

I just bought a 10 inch heavy barrel upper for my M16A1 lower.  I added the collapsible buttstock to make it a commando.  For it to run flawlessly I needed to change the buffer from an H to a 3H.  It cycles a little slower, but is 100 percent reliable.

Hope that helps.

Originally Posted By CapitalOrdnance: I was one of the developers of the Arms-Tech Compact M-16 system, a 9.5"bbl gas-trap chambered systemand have fired a lot of 5,56mm ammo in the M-16 weapons systems. We got 14.5" bbl. velocities out of our 9.5"bbl. and less chamber/lead erosion.

All of the actual tests I have seen showed 9.5 inch velocites from a 9.5 inch barrel. The 14.5 inch velocity claim would not likely hold up to a real test. If it did, I would RUN and buy one.

By the way I did pick up a Arms Tech 9.5" upper.The one with gain twist polygonal rifling.They claim same velocities out of their 9.5 as the 14.5" standard M-4s.Going to the range with my Chrony tomorrow to find out.Will report......................

Some very smart people believed what was claimed about it. The actual tests I saw showed the velocity equal to a 9.5 or 10 inch barrel. Think HK-53 velocities (polygonal 9.5 inch barrel).

BTW, I am not saying it is not a great upper! I would be very excited about it for all of its nice features. I like polygonal rifling and the gas-trap. Gain twist has not been shown to offer anything in terms of velocity or accuracy as far as I know and David Tubb ruled it out for his competition barrels. Just don't expect it to have more velocity than a Colt 10.5 inch barrel.

I am tempted to offer a $10,000 bet over this. I am that confident that a 14.5 inch conventional barrel with the same chamber-reamer would beat it, as expected. My only hesitaton in offering the bet would not be that I would lose, but just that it would be hard to arrange to get another barrel made with the same chamber-reamer. I would basically need to watch the barrels being made.

I'm planning to build an SBR when I get home from the sandbox and based on this great discussion, I'm going to go with the LMT 10.5" upper.  Any suggestions for the lower?  I was planning on Bushmaster - I'd like to get a Colt lower, but the pins / holes won't work with LMT's upper unless I find a pre-ban, correct?  Is that my only option for Colt?

Am I correct in assuming that I can't legally use an M16 / M4 bolt carrier group in a regular semi-auto SBR?  Thanks,

Dave

Originally Posted By 3ACR_Scout: I'm planning to build an SBR when I get home from the sandbox and based on this great discussion, I'm going to go with the LMT 10.5" upper.  Any suggestions for the lower?  I was planning on Bushmaster - I'd like to get a Colt lower, but the pins / holes won't work with LMT's upper unless I find a pre-ban, correct?  Is that my only option for Colt? Am I correct in assuming that I can't legally use an M16 / M4 bolt carrier group in a regular semi-auto SBR?  Thanks, Dave

The Colt lower will work fine.  The fire control pins (trigger and hammer pins) are large on the Colts so if you buy a stripped lower just be sure to get a lower parts kit for the Colts.

Colt is now shipping the M16 / M4 bolt carrier group in all LE rifles so you should be fine if that is what you want to use.

Originally Posted By ar15inmn: The Colt lower will work fine.  The fire control pins (trigger and hammer pins) are large on the Colts so if you buy a stripped lower just be sure to get a lower parts kit for the Colts. Colt is now shipping the M16 / M4 bolt carrier group in all LE rifles so you should be fine if that is what you want to use.

Thanks for clearing that up - I got a little mixed up there - for some reason I was thinking that the mounting / takedown pins (I forget the "official" name) for attaching the upper receiver were a different size on the post-ban Colts.  I forgot that the change just covered the fire control group.

That's interesting about the Colt LE rifles - I had always heard that the M16 / M4 BCG was a machine gun component and therefore couldn't be used in an AR.

Thanks again,

Dave

Dave,

The older Colts did have a large hole front pivot pin.  The newer lowers have the small hole front pivot pin.  If you stick with a newer production lower you are fine but it is good to keep in mind when you start looking.

Ok guys, I've got one more question.  I've heard several people make the comment that Colt sticks with the 11.5" barrel because of its proven reliability, but now I see that Colt has produced 10" barrel versions of the 6920, 6721, and 6320 rifles.  Seems to me that if the 10.5" barrel is temperamental, the 10" barrel is definitely going to have issues.

Anyone have any experience with the 10" version of these weapons?  Did Colt make any modifications to the gas system to address the reliability issues with a barrel this short?  Any reports from the range about how they operate?

Thanks,

Dave