Considering a colt lmg upper

[Battering ram NIB]

Ive read up a bit on these. I know they can be open or closed bolt setup

If you buy the closed bolt setup all your getting is a thicker barrel and heavy duty gas tube. Am I missing anything else ? I wouldn’t mind owning a m16 upper i can shoot the p*ss out of

Does it use a normal buffer and spring

I see things that confuse me about green springs and hydraulic buffer

I don’t want to change out lower parts to shoot it open bolt

 

[nuge]

I have the two types of LMG uppers shown below and both have the heavy bbl. Top is the newer LSW type and the bottom is the original LMG - both are built by Colt. Shooting in closed bolt is a lot of fun - a beta mag dump is no problem. I always use the green spring and hydraulic buffer. Either a registered receiver or RDIAS will work in closed bolt mode. Even though I have a couple of open bolt parts kits, I have yet to try them out until researching a little bit more about the rumor of lower receiver damage with the open bolt set up. Also open bolt config. won't work with an RDIAS. In any case the fun factor is big with an LMG upper and should be a part of an M16 shooter's gear in my opinion.

 

[Mr.Maim]

I looked at these for a while for my RR and simply could not justify the $3000+ price tag for what it is, for what I intended to do with it: full-auto blasting.

Got an FN Herstal 20" M16A2 upper for $525 and $125 for Colt complete bolt/carrier, and have been happily blasting away ever since. Accurate as heck!


I'm not going to lie, I still want an LMG upper, but it'd end up being a wall hanger.

 

[Hawksnest]

I shoot the original Colt LMG upper with a closed bolt and the hydraulic buffer with green spring. The hydraulic buffer slows the rate of fire and I can get accurate 2 shot bursts. Cool upper. My $0.02.

 

[Battering ram NIB]

If the kit comes with the open bolt is it simply swapping bolts to a standard bcg?

Do you need the special buffer? Or is that just to slow it down?

The kit I’m looking at includes the open bolt bcg which I don’t want

 

[Hawksnest]

Open bolt uppers need several other different parts needed to run it open bolt.

 

[Paul Kersey]

Cheaper alternative would be the Colt 741 upper (or clone). Basically HB AR15A2 with M60 bi-pod. Not a great success in the field (can't quick change barrels) but can be a hoot to shoot with a RR lower.

 

[Battering ram NIB]

ive done some pricing research and have found they have sold $1500-1950 consistently..some NIB, some minty used

ill grab one for that price range

 

[A&S Conversions]

As far as what you get, with the original Colt LMG upper, is a chrome lined barrel that is almost an inch in diameter under the hand guards. But to me the biggest difference between a standard 20" HBAR and the LMG is the gas block and gas tube. The gas block is designed for use with a special heavy walled tube. A standard front sight/gas block is designed for a standard lightweight curved gas tube. The LMG upper has the same inside diameter, but the tube wall is much thicker than a standard gas tube. With sustained full auto fire with a standard upper, the gas tube gets so hot that the stainless steel gas tube gets too soft to contain the bleed off gas that works the works the bolt group. The gas tube ruptures and the gun becomes a single shot. That heavier walled gas system is what makes the LMG upper worth the extra money. The LMG gas system can handle much more sustained full auto fire than the standard AR gas system.

The open bolt fire control system uses a full auto hammer that is notched at the top and a modified bolt carrier that the hammer notch fits into, holding the bolt group back. The fire control is specific for the open bolt. In a standard AR, because of the angled surfaces of the trigger and hammer, when the trigger is pulled the hammer actually goes down before it is released from the trigger. This action is what releases the bolt/carrier assembly from the notched hammer. The recoil spring drives the bolt/carrier assembly forward, stripping and chambering a round. The G.I. auto sear releases the hammer, which strikes the firing pin. This fire control system is designed for full auto only, no select fire.

As far as springs and buffers, "amphibian" on an other site has gotten great results from an A5 buffer tube, Kynshot 9mm buffer, and Tubbs flat wire spring. That is his setup for pistol caliber and rifle caliber configurations. He has stated that he installs a .308 Tubbs spring for use with his belt fed Shrike for the additional spring power needed to strip rounds from the belt. His typical ROF is 650 to 675 RPM. These are current production, off the shelf components, not out of production for 30 years parts.

While the increased mass of the LMG barrel and heavier gas system helps, the barrel is still going to get hot. I went another route. What kept the machineguns of WW I running for tens of thousands of rounds? A water jacket. I built a few of these 10 years ago. I put one up for sale to gauge interest. At $2,000 each (15% above my actual cost for parts) I sold the one extra unit with a couple of guys that were "interested". With that level of interest, I didn't make any more. Here is my wife running 500 rounds using a custom/KNS setup with a Valkyrie Armaments belt fed system:

http://youtu.be/RFcxuOzsoXA

At the time green tipped Federal was $400 per thousand. So that is a $200 minute. Not something I do all the time, but if what you want is sustained full auto fire, water cooled is the only way to go. I have over 8,500 rounds through that upper with mostly 100 or 200 round bursts. I don't see any throat erosion yet. Between the custom work, the belt fed system, and the parts I have around $7,500 in the semiautomatic host gun pictured. Sustained fire full auto is not cheap, but boy is it fun. YMMV.

Scott

 

[MG34_Dan]

Here is one of our MG videos from over ten years ago. There's an LMG being fired in here. If you want to know everything/anything about using an LMG upper in bolt open bolt and closed bolt use, contact Mongo.

 

[USSarizona]

Other than the 741, is anyone aware of any relatively sufficient commercial alternatives to the Colt LMG for an LMG upper?

 

[A&S Conversions]

Other than the 741, is anyone aware of any relatively sufficient commercial alternatives to the Colt LMG for an LMG upper?

There are many manufacturers that make a heavy barreled 20" upper. I know of no manufacturer that makes a specialized front sight/gas block that uses a much heavier walled gas system tube. Of course you could buy three or four off the shelf 20" HBAR uppers for the price of a Colt LMG upper and rotate them. Or seal off the gas system and put a water jacket around the barrel and pound on it all you want.

There is also the Titan piston upper. I bought two 14.4" for $650 each and two 10" for $750 each. I had Northeast Gunworks replaced the original stainless steel barrel with a double chrome lined FN barrel. I have not run it yet. No gas tube to melt and rupture.

There is no way around it. The more rounds down the barrel, the hotter the barrel gets and the more accelerated the wear of the bore. A thicker barrel heats up more slowly. Unless the barrel is cooled some how. That's why I had the first water cooled upper made. YMMV.

Scott

 

[Samuel_Hoggson]

Does anyone know whether the gas port is located or sized differently vs 20" rifle barrels? Ask b/c both factory LMG uppers I've seen/shot at shoots seemed relatively undergassed. Seemed like they needed to be broken in. Never seen that with a Colt rifle upper. Both were closed bolt, dropped onto registered receivers with no changes made.

 

[gman552]

Does anyone know whether the gas port is located or sized differently vs 20" rifle barrels? Ask b/c both factory LMG uppers I've seen/shot at shoots seemed relatively undergassed. Seemed like they needed to be broken in. Never seen that with a Colt rifle upper. Both were closed bolt, dropped onto registered receivers with no changes made.

What receiver extensions (RE), buffer springs and buffers were installed on the RRs?

The LMG upper will not run properly with a carbine RE and spring.

From personal experience, it will run perfectly with a rifle RE, using either the LMG hydraulic buffer/LMG green spring combo (for slower ROF), or a standard rifle buffer/rifle spring.

Here is a post of mine on AR15.com showing the springs and buffers, as well as my buffoonery with insufficient charging handle retraction :silly

BTW, the LMG green spring has a faintly green tint to it, don't expect it to be a bright green color or anything like that.

From reports, the VLTOR A5 system will also work. Please see this video: M16 LMG (on Vimeo)

 

[Samuel_Hoggson]

What receiver extensions (RE), buffer springs and buffers were installed on the RRs?

These were rifle extension tubes, standard rifle buffer and spring. The LMGs uppers were brand spankin' new. Maybe just anecdotal then?

 

[gman552]

These were rifle extension tubes, standard rifle buffer and spring. The LMGs uppers were brand spankin' new. Maybe just anecdotal then?

Huh.

Maybe the ammo didn't have enough oomph?

 

[Samuel_Hoggson]

Maybe the ammo didn't have enough oomph?

So long ago I don't remember exactly what was used. But it was brass cased in one (cuz that's all the guy used). Steel in the other upper belonging to my buddy. The ammo cycled fine in everything else we had for uppers.

 

[A&S Conversions]

There is a world of difference between brass cased. 223 Remington and Green tipped 5.56X45 NATO ammo. Since the LMG upper was designed for very high volume of fire, which can make for gas port erosion, higher powered NATO spec ammo, and a lighter powered spring to slow cyclic rate, I would think that the gas port would be designed for that application. If a new barrel with no erosion, under powered .223 ammo, and a stiffer standard spring was used, I could see new uppers running sluggishly. Any one of those things would tend to have a slowing effect. If all three of those factors were present,
I could see a profound effect on function. Commercial uppers tend to run bigger gas ports as they tend to be run with lower volumeof fire with lower power ammo. VMMV.

Scott

 

[Samuel_Hoggson]

That makes sense, Scott. Even if the gas port is the same diameter as on 20" rifles, it will be longer thanks to a thicker barrel wall. That should result in less gas flow into the tube.

 

[Battering ram NIB]

Upper sold at $2500 which I felt was a nutty price for a used upper

Obviously they have become collector items and priced as such

I’ll wait for a better deal