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Posted: 5/16/2021 9:53:30 PM EDT
[#1]
Quote HistoryQuoted: There does seem to be a fascination for an LMG upper, me included. And, some of us are rolling our own. Or, rolling a LMG-ish. https://i.imgur.com/ppRHYyT.jpg Blem unfinished M4 upper receiver. (Finished with forward assist "hump" removed) 20" 4140 1:8 Nitrided Bull barrel (0.980 under HGs, .936 at gas block) DPMS A2 Type sight base for Bull barrel Triangle HG cap opened up to .938 Cavalry Mfg. C5 "Fat" oval handguards (They're really FAT) M249 bipod on barrel adaptor pivot Rail mounted folding carry handle (It's Chinese, but the only game in town) Everything else standard A2 parts (Charging Handle, Semi Bolt and Carrier, Port Cover, Delta Ring Assy., Sight Parts, Flash Hider and Crush Washer) It's still early in the construction stage. And, I still have a lot of making or modifying of parts to do. Also, there IS a free downloadable file for 3D printing the handguards available. 3D Print LMG Handguard There is also this: LSW Repro Left HG That's cool. I want to do something similar but I have a 20" Hbar barrel. I have those same hand guards on the way. It will be a sweet set up with an FRT and 60 round mags. I have some Schmeisser 60 rounders and am wondering if they'll be too tall. One thing I need to do is figure out what bipod to use. Those M249 bipods are kind of pricey. |
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Posted: 5/17/2021 6:16:07 AM EDT
[#2]
Quote HistoryQuoted: There does seem to be a fascination for an LMG upper, me included. And, some of us are rolling our own. Or, rolling a LMG-ish. https://i.imgur.com/ppRHYyT.jpg Blem unfinished M4 upper receiver. (Finished with forward assist "hump" removed) 20" 4140 1:8 Nitrided Bull barrel (0.980 under HGs, .936 at gas block) DPMS A2 Type sight base for Bull barrel Triangle HG cap opened up to .938 Cavalry Mfg. C5 "Fat" oval handguards (They're really FAT) M249 bipod on barrel adaptor pivot Rail mounted folding carry handle (It's Chinese, but the only game in town) Everything else standard A2 parts (Charging Handle, Semi Bolt and Carrier, Port Cover, Delta Ring Assy., Sight Parts, Flash Hider and Crush Washer) It's still early in the construction stage. And, I still have a lot of making or modifying of parts to do. Also, there IS a free downloadable file for 3D printing the handguards available. 3D Print LMG Handguard There is also this: LSW Repro Left HG Weird. Double tap. |
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Posted: 6/2/2021 9:46:31 PM EDT
[#3]
I had a "user" Colt LMG (A2) Upper for a few years that I would mess around with on our range. Throw it on an A2 lower and burst, was stupid repeatable with zero rise. I sold that Upper but still have a new in wrapper one that is just sitting. I have a Colt big pin lower with a Geissele SSA trigger set up with a Colt CS Stock that I might mock it up on and a spare 2X ACOG. Semi-Auto doesn't seem right for that upper but I know it would be accurate.
S/F Al |
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Posted: 6/5/2021 5:21:24 PM EDT
[#4]
Any way you one make a 249 bipod adapter that’d mount to a picatinny or M LOK rail? I want a bipod for one of my ARs but everything on the market is insufficiently durable with the exception of the very expensive BLK LBL.
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Posted: 6/7/2021 1:46:06 AM EDT
[#5]
I'd be happy with everything in front of the upper. I'd prefer to use one of my big hole uppers, but I'd buy the whole thing if that was the only way to get one.
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Posted: 6/25/2021 5:39:17 PM EDT
[#6]
Sven, IM sent - check your inbox. @Manticore_Arms
Mark |
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Posted: 6/26/2021 1:28:03 AM EDT
[#7]
I'm hoping something comes to fruition as a finished product.
In the meantime, I'm proceeding with a modern LMG-esque build using an old chrome-lined Bushmaster 20" HBAR barrel I found on GunBroker. I'm going with the Aero M4E1 Enhanced upper because I like how the barrel nut is setup like a Colt 6940, threaded internally (which is said to offer some benefit in barrel stability but idk) and it will free float certain rails with what hopefully proves to be a rock solid interface.  Specifically this Spikes BAR2 13.2" rail, since I couldn't locate anything with better ventilation (even MLOK rails) and I think the Picatinny interface will be a better hold for the Magpul bipod anyway, when it gets hot up there by the lo pro gas block.  It's also got a large internal diameter, so the JP thermal dissipater will easily fit under it, and has plenty of clearance. Should also contribute to good air cooling. We'll see.  I'm thinking about adding thermal grease between it and the barrel. I can't find where anyone's done that before, but it seems like it wouldn't hurt. (I'll get some with a high melting point so it won't drip out of there.) Also looking at the V7 inconel gas tube. They say it won't fit the M4E1 upper (probably because of the increased diameter of the tube where it needs to go into the front section of the M4E1 upper) so I think I'll ream the front until it fits. Undecided. Maybe standard gas tube is good enough? Going with the old hydraulic Colt LMG buffer (and spring) unless you guys think something else is better.  Attached FileKynShot? Should be a fun project. 
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Posted: 9/12/2021 8:33:54 AM EDT
[#8]
I’d be in line for components to build the LMG upper.
If the hand guards are true to original style, where a barrel mounted carry handle would work. This way the A2 upper can be used, instead of a flat top. Has anyone actually 3D printed a set of these yet? I’m Curious to see what they would look like. |
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Posted: 9/12/2021 5:16:10 PM EDT
[#9]
I have had a LMG upper and used it one time in ten years. It is just a closed bolt and no weird buffer. It has the thickest barrel you have seen, and he gas tube is over built also. Carry handle and bipod.
What is a clean unit worth? |
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Posted: 9/13/2021 1:06:31 PM EDT
[#10]
Quote HistoryQuoted: I have had a LMG upper and used it one time in ten years. It is just a closed bolt and no weird buffer. It has the thickest barrel you have seen, and he gas tube is over built also. Carry handle and bipod. What is a clean unit worth? @Chas8008 Assuming it is actual Colt and not on e of the Blackthorne made repros, $2500+ on Gunbroker. Sven Manticore Arms |
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Posted: 9/13/2021 1:23:45 PM EDT
[#11]
I'm very interested at $1k I'd order one up.
I need to find all the open bolt internals. I love smooth shooting machineguns. |
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Posted: 9/13/2021 2:05:30 PM EDT
[#12]
Quote HistoryQuoted: @Chas8008 Assuming it is actual Colt and not on e of the Blackthorne made repros, $2500+ on Gunbroker. Sven Manticore Arms Quote HistoryQuoted: Quoted: I have had a LMG upper and used it one time in ten years. It is just a closed bolt and no weird buffer. It has the thickest barrel you have seen, and he gas tube is over built also. Carry handle and bipod. What is a clean unit worth? @Chas8008 Assuming it is actual Colt and not on e of the Blackthorne made repros, $2500+ on Gunbroker. Sven Manticore Arms I cannot say it is colt without lay my eyes on it again. but I'm 99% sure it is. I know the carrier is Colt but the rest is just a blur perhaps I have too many guns. are there any tall tale giveaways? I was fortunate enough that this gun was part of a deal in which I got my lightning link for $5k about 10 years ago Don't get me wrong I like the upper it's super cool but it just sits in my safe. I just sold a bunch of guns and It feels good I feel less like a curator at a museum and more like weight has been lifted off my shoulders. Maybe thinning the herd a little bit more in the future may do the same again |
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Posted: 9/13/2021 9:53:15 PM EDT
[#13]
@Chas8008
If it has an A3 upper or an A2 upper with forward assist, it is most likely a Blackthorne repro. If it has an A2 upper without forward assist (there was no point to a forward assist as it was an open bolt design, although it will work with a standard closed bolt carrier group) it is 99% sure it is real colt. If you post pics with the handguards removed I can tell in about 2 seconds if it is legit Colt or not (there should be some markings on the barrel) Sven Manticore Arms |
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Posted: 9/13/2021 9:54:11 PM EDT
[#14]
Quote HistoryQuoted: @Chas8008 If it has an A3 upper or an A2 upper with forward assist, it is most likely a Blackthorne repro. If it has an A2 upper without forward assist (there was no point to a forward assist as it was an open bolt design, although it will work with a standard closed bolt carrier group) it is 99% sure it is real colt. If you post pics with the handguards removed I can tell in about 2 seconds if it is legit Colt or not (there should be some markings on the barrel) Sven Manticore Arms |
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Posted: 9/16/2021 11:13:50 AM EDT
[#15]
Quote HistoryQuoted: I'm very interested at $1k I'd order one up. I need to find all the open bolt internals. I love smooth shooting machineguns. @jaqufrost Most of the lower parts are here. |
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Posted: 9/16/2021 11:15:08 AM EDT
[#16]
Quote HistoryThanks!
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Posted: 9/16/2021 11:43:33 AM EDT
[#17]
Quote HistoryQuoted: Thanks! Glad to see these are available. Does anyone have any idea what it would take to modify this FCG to have closed-bolt operation with the selector in SEMI, and open-bolt operation in AUTO? (Like some of the IAR prototypes) Seems like the selector would need to pivot the complex autosear assembly to retract the hammer enough to release the bolt carrier, and then leave the hammer resting on the trigger's primary sear surface (like a normal closed-bolt trigger/hammer). |
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Posted: 9/16/2021 11:53:09 AM EDT
[#18]
Quote HistoryQuoted: Yes, thanks for that link. Glad to see these are available. Does anyone have any idea what it would take to modify this FCG to have closed-bolt operation with the selector in SEMI, and open-bolt operation in AUTO? (Like some of the IAR prototypes) Seems like the selector would need to pivot the complex autosear assembly to retract the hammer enough to release the bolt carrier, and then leave the hammer resting on the trigger's primary sear surface (like a normal closed-bolt trigger/hammer). The regular sear surface on the open bolt hammer is removed. You would have to weld one back on. There is also no disconnector in the system so some how one would have to be made for semi auto functioning. I have been wanting to see what the select fire open bolt group looked like but have never found a picture of one. |
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Posted: 9/16/2021 12:02:57 PM EDT
[#19]
Quote HistoryQuoted: I have been wanting to see what the select fire open bolt group looked like but have never found a picture of one. I believe you're correct regarding the required modifications. Seems like it'd be the best of both worlds. Between the 2 currently available FCG options, I think I'd favor closed-bolt operation. You have an open-bolt LMG right? What's your opinion? |
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Posted: 9/16/2021 12:10:52 PM EDT
[#20]
Someday I want to fab up an M231 type FCG and try it as well.
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Posted: 9/16/2021 6:00:18 PM EDT
[#21]
Quote HistoryQuoted: Yeah, same here. I believe you're correct regarding the required modifications. Seems like it'd be the best of both worlds. Between the 2 currently available FCG options, I think I'd favor closed-bolt operation. You have an open-bolt LMG right? What's your opinion? Yup, I have one of the ones tested by the Marines and its open bolt. I love the open bolt but I'm into collecting really controllable and rare LMGs. Let's face it, a M16 is useless unless you just like mag dumping or you are going to shoot it as an SMG or LMG. Full auto carbines/assault rifles really are not that fun. I have a Stoner 63a so I have no desire for a beltfed M16 that's a poor beltfed. |
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Posted: 9/16/2021 6:06:34 PM EDT
[#22]
Quote HistoryQuoted: I have never been able to wrap my head around the concept of an LMG or SAW without a quick change barrel feature. The M249 is rated to fire 800 rounds cyclic, and the guy carrying it has 800 rounds. When is he going to need to change barrels? |
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Posted: 9/16/2021 6:18:25 PM EDT
[#23]
Quote HistoryQuoted: The M249 is rated to fire 800 rounds cyclic, and the guy carrying it has 800 rounds. When is he going to need to change barrels? SAW barrels get hot fast. Change them every 200 rds if you can. It literally takes all of a couple seconds. |
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Posted: 9/16/2021 6:43:51 PM EDT
[#24]
Id be down if it works with a FRT.
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Posted: 9/16/2021 7:37:33 PM EDT
[#25]
V7 offered an inconel gas tube, and may still. From a functional standpoint it may do the job as well as the colt heavy gas tube. Of course inconel used on a colt heavy profile gas tube would probably be better...
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Posted: 9/16/2021 7:44:12 PM EDT
[#26]
I'd buy one for my Colt RR if large pin.
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Posted: 9/21/2021 8:21:15 PM EDT
[#27]
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Posted: 9/21/2021 8:32:01 PM EDT
[#28]
Quote HistoryQuoted: I prefer the IAR myself as the LMG holds no appeal to me Have you tried both? The LMG is said to be smoother and more stable (in either open or closed bolt configuration). Not sure which can take the heat better (assuming bolts are the same). |
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Posted: 9/21/2021 10:43:05 PM EDT
[#29]
Quote HistoryQuoted: Nice. Have you tried both? The LMG is said to be smoother and more stable (in either open or closed bolt configuration). Not sure which can take the heat better (assuming bolts are the same). Quote HistoryQuoted: Quoted: I prefer the IAR myself as the LMG holds no appeal to me Have you tried both? The LMG is said to be smoother and more stable (in either open or closed bolt configuration). Not sure which can take the heat better (assuming bolts are the same). I have both, the LMG is a lot smoother shooter (even in closed bolt) thanks to the hydraulic buffer and rifle length buffer tube. I would choose the LMG every day of the week over the IAR. Sven Manticore Arms |
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Posted: 9/23/2021 12:20:05 AM EDT
[#30]
I do not own an LMG upper as I could just never get over the aesthetics of it.
I know, I know. Who cares what it looks like if it works it’s just I could never justify buying one just based on the price they get for them and the look. |
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Posted: 9/23/2021 8:09:51 PM EDT
[#31]
I'd be all over it. I think it's a great design.
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Posted: 10/25/2021 12:25:18 AM EDT
[#32]
This thread got me hooked on the LMG design. I’m building one, with a few minor changes. Still waiting for hand guards, and have some machine work on the bipod mount and carry handle( both from a SAW)
 Attached File |
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Posted: 10/25/2021 8:43:50 AM EDT
[#33]
That's going to be sweet.
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Posted: 10/30/2021 8:20:42 PM EDT
[#34]
Quote HistoryQuoted: Going with the old hydraulic Colt LMG buffer (and spring) unless you guys think something else is better. https://www.ar15.com/media/mediaFiles/13082/LMG_buffer_jpg-1991599.JPG KynShot? Should be a fun project. The LMG buffer is perfect if using an fix rifle stock, but have you considered using the A5 buffer system? https://bravocompanyusa.com/bcm-intermediate-buffer-system-a5-mounting-kit/ Then you could use a carbine stock. |
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Posted: 11/2/2021 6:49:59 PM EDT
[#35]
With hand guard mocked up.
 Attached File |
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Posted: 11/3/2021 11:53:39 AM EDT
[#36]
Quote HistoryQuoted: With hand guard mocked up. https://www.ar15.com/media/mediaFiles/533696/9F9B9810-4CC7-4755-9CB2-E07343858A91_jpe-2152760.JPG @Flynnchester Where did you get the handguards from? 3D printed? Sven Manticore Arms |
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Posted: 11/3/2021 2:51:32 PM EDT
[#37]
From a member on the retro forum. I had purchased a retro pistol brace and it was so well made I asked if he could do these.
He said it was a lot of work, but they came out real nice. Definitely have to fit them to your parts. I love the look of them on the rifle.  Attached FileThis is before I fit the front of them around the barrel. I still have to make heat shields as this PLA will not take a ton of heat. Probably cost $$$$ but I would like to see them finished in carbon fiber, or something similar. But for my project these are fine for now. |
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Posted: 1/2/2022 1:04:26 AM EDT
[#38]
Bumping this thread back to the top. I want to build a LMG ish upper as an RLL host. I know some are real sticklers for everything being a perfect clone, however I am not. I would want something that looks reasonably like an LMG upper and is built to handle sustained closed bolt full auto fire. I would be totally OK with minor upgrades that don't look too much unlike the original but do enhance the function . (This gun is not and would never be a real colt lmg). Seems like the most difficult parts are the handguard and barrel/carry handle with bipod mount.
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Posted: 1/5/2022 11:07:46 AM EDT
[#39]
Quote HistoryQuoted: The LMG buffer is perfect if using an fix rifle stock, but have you considered using the A5 buffer system? https://bravocompanyusa.com/bcm-intermediate-buffer-system-a5-mounting-kit/ Then you could use a carbine stock. Quote HistoryQuoted: Quoted: Going with the old hydraulic Colt LMG buffer (and spring) unless you guys think something else is better. https://www.ar15.com/media/mediaFiles/13082/LMG_buffer_jpg-1991599.JPG KynShot? Should be a fun project. The LMG buffer is perfect if using an fix rifle stock, but have you considered using the A5 buffer system? https://bravocompanyusa.com/bcm-intermediate-buffer-system-a5-mounting-kit/ Then you could use a carbine stock. As a baseline here is a Colt LMG on a lower configuration you would find on a MK18.  Same upper and just changing to the A5 tube Kynshot RB5007 and 556 Tubb flat spring.  Note that I use this same buffer tube, buffer and spring in about 95% of all of my full auto M16 configuration in various calibers. I have this documented here: https://c3junkie.com/?page_id=977 I also want to stress that the heavy gas tube on the LMG shouldn't be overlooked, not only is the outer diameter larger so is the INSIDE diameter. As mentioned here: http://www.sadefensejournal.com/wp/the-colt-lmg/2/ That increased volume of the gas tube really helps to smooth out the action. I had someone custom make a large diameter rifle length gas tube and the configuration below has got to be the smoothest suppressed 556 setup I have every fired. Zero gas to the face and great cyclic rate. 16" Rifle length gas, custom fat rifle length gas tube, A5 buffer tube, RB5005 Kynshot hydraulic buffer, 556 Tubb flat spring, custom spacer to prevent over travel. Surefire OBC for a little increased carrier travel as well as enhanced cam pin geometry. 576 RPM  |
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Posted: 1/11/2022 10:47:11 PM EDT
[#40]
Quote HistoryQuoted: I have both, the LMG is a lot smoother shooter (even in closed bolt) thanks to the hydraulic buffer and rifle length buffer tube. I would choose the LMG every day of the week over the IAR. Sven Manticore Arms BUMP ! Doesn't then the IAR come closer with a full length tube AND a hydraulic buffer like from Kynshot / Blitzkreig ? I had a shot at a factory Colt semi-auto "LMG" at Morphys but had a mix up with their phone in broker. Thought I was the high bidder. Nope ! Gun sold for <3500. I have 2 M16 registered lowers left and there are Colt open bolt triggers out there for sale. All combined would have made something kinda special . |
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Posted: 1/12/2022 4:26:45 PM EDT
[#41]
Quote HistoryQuoted: BUMP ! Doesn't then the IAR come closer with a full length tube AND a hydraulic buffer like from Kynshot / Blitzkreig ? I had a shot at a factory Colt semi-auto "LMG" at Morphys but had a mix up with their phone in broker. Thought I was the high bidder. Nope ! Gun sold for <3500. I have 2 M16 registered lowers left and there are Colt open bolt triggers out there for sale. All combined would have made something kinda special . Quote HistoryQuoted: Quoted: I have both, the LMG is a lot smoother shooter (even in closed bolt) thanks to the hydraulic buffer and rifle length buffer tube. I would choose the LMG every day of the week over the IAR. Sven Manticore Arms BUMP ! Doesn't then the IAR come closer with a full length tube AND a hydraulic buffer like from Kynshot / Blitzkreig ? I had a shot at a factory Colt semi-auto "LMG" at Morphys but had a mix up with their phone in broker. Thought I was the high bidder. Nope ! Gun sold for <3500. I have 2 M16 registered lowers left and there are Colt open bolt triggers out there for sale. All combined would have made something kinda special . The hydraulic buffer definitely is a big part of the LMG upper being smooth, the other part is longer rifle length gas system and heavier barrel. Certainly a hydraulic buffer in the IAR upper would smooth it out, but cyclic rate is still going to be higher. To be honest the IAR upper is really nothing more than a monoithic upper colt with standard gas tube and a big aluminum heatsink lower section. If you swapped out the heatsink for a standard colt monolight lower forend portion you would not be able to tell the difference functionally from a standard colot monolithic upper. Sven Manticore Arms |
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Posted: 1/13/2022 6:35:10 AM EDT
[#42]
Quote HistoryQuoted: Doesn't then the IAR come closer with a full length tube AND a hydraulic buffer like from Kynshot / Blitzkreig ? See my post above with a factory Colt LMG, I'm getting in the 600's with the A5 tube, Kynshot and Tubb 556 spring. I have some of this documented here: https://c3junkie.com/?page_id=977 If you read that link, you will see that you get close to the same amount of force using a Tubb 556 flat spring when the bolt is open vs closed compared to a rifle length spring. A2 spring (new) 9.1lb closed, 16.7lb open Tubb Flatwire 10.5lb closed, 16.3lb open The Tubb flatwire spring is the only spring I know of that is advertised to be used in BOTH a carbine OR a rifle length buffer tube. (obviously works in an A5 since it is in the middle). Now if you really wanted to, you could go with a Tubb flat spring in a rifle length buffer tube and longer rifle length buffer and get it to be a bit slower but as I posted above, I'm already getting in the 600's and I still retained the ability to have a collapsible stock so why bother with the rifle length tube unless you just want it for looks or just like a fixed stock better.  |
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Posted: 1/13/2022 1:59:16 PM EDT
[#43]
Might a gas adjustable bolt allow regulation of the cyclic rate ?
Like a 2A or Bootleg ? |
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Posted: 1/13/2022 3:34:44 PM EDT
[#44]
Quote HistoryQuoted: Might a gas adjustable bolt allow regulation of the cyclic rate ? Like a 2A or Bootleg ? Are you saying you want slower than either of those?? IMHO, those are already where I want to be at. Easy to make them go faster..... not so easy to make them slower than what I have already done as the gas is already regulated on my 16" Rifle and I didn't want to mess with the gas on a factory LMG although an adjustable carrier would work. Below is even slower using a Ferfrans RRS carrier to slow it down super slow but I find the RRS to be too bouncy. Something about the delaying of the autosear like that doesn't feel smooth to me.  |
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