I’ve been thinking about taking another run at building a lightweight dissipator style rifle. I’ve looked into most of the obvious options, but I thought I’d ask about cutting down a 20" gov’t profile barrel to 16" since that would be a fairly simple way to get the barrel I want. The problem is that I was under the impression that it was hard to get a rifle length gas system to function with a 16" barrel. Has anybody ever been successful at doing this or should I just go back to one of my other plans?
Free bump, I just had the same exact idea and was going to post in regards to the reliability 
Cutting down to as short as possible 14.5ish and pinning and welding a PWS FSC 556 on it to keep it legal, beyond 16" also turned down close to lightweight, for the gf.
you can probably get a 16" rifle-length weapon to run reliably-enough, depending on your application and ability to stay consistent with ammunition. if this is going to be a fun-only gun, or a competition-only gun, then i’d say DO IT! and let us know how it works. i’d get some professional opinions on gas port sizing- ADCO Steve, GotM4, anybody else you can think to shoot an email to.
might turn out to be a really good shooter that eats any and all ammo type. i’ve seen a couple of 16/rifle weapons that did shoot quite well, in the last decade. but also be prepared to have a potential pain in the ass.
the other option, if you’re looking to keep the FSB way out by the muzzle but not have to fuck with the gas system- have them plug the gas port and re-drill at mid-length, then use a low-pro gas block under the handguard and keep your FSB out where it lives. this is something that’s on my “to build someday” list.
This was going to be my ranch rifle so reliability is important. Ammunition consistency wouldn’t be a big issue since I always use BH 55gr soft point for my ranch rifles. If I had more money to throw around I’d definitely give this a go, but as of right now, if I’m gong to spend the money on another project, it needs to be a sure thing. I do see though that gunny’s surplus has used A2 barrels for either $175 or $125 so it wouldn’t be too expensive to try one.
KKF cut down some early M16/SP1 barrels for me. They ran fine with all the ammunition I tried. One in particular saw a lot of use. Kurt opened the port after the cut, but I forget the dim he used. I don’t think I have any of those barrels anymore to measure it for you.
I know others who had their LESO M16s cut down. Some had them done expertly, some used their local smith/gun-guy. They got the results they should expect.
Depending on the barrel profile, there may or may not be a sufficient shoulder to torque a flash hider or other muzzle device against. Some vendors offer solutions for that. One of mine had a angled collar that worked well.
ADCO does good work, and would likely lead the list of those to do the job for you.
I’d hesitate to chop a genuine M16A2 barrel for the project, unless I knew it was what I really wanted. I feel guilty enough doing that to all those nice SP1 barrels.
Have you considered cutting or swapping the FSB on a standard 16" barrel, installing an extended rail and adding a FS? This would be more flexible, functionally and financially, in the longer term.
This will only work if you have an HBAR.
The best way would be to start with a 16" Mid barrel. Forward of the gas block turn the barrel down to .625" and pin a .625" FSB at the rifle position.
ADCO will do anything you ask them to do, but that doesn’t mean it’s the best thing. Steve will tell you not to go shorter than 18" if you plan on ‘using’ your rifle. If it’s a plinking gun, then you can go 16".
Actually, ADCO is coming out with a new dissipator barrel, they call it the cruiser. I’ll be picking one up. You could sell yours and buy one.
I had mine cut to 17.5" and it works fine. Just make sure to tell Steve that you want the ports opened enough so you can shoot Russian ammo.
It’s a good deal lighter, but you may also want him to flute it while he has it at the shop.
Mine:
ADCO would’ve been “the list” for this project. I’ll have to shoot them an email. I would be trying to get a light and soft shooting ar for the gf. A turned down BCM middy will probably be the way to go reliability wise.
I have a 20" rifle cut to 16", rifle length gas, it ran fine prior with a rifle length buffer and A2 buttstock.
This last year I put the KX3 on it thinking I needed and extra boost in pressure for a carbine stock.
It functions as seen with an H buffer and new carbine spring.
Ultimately, I do want to test it sometime in the future with a A2 flash hider and carbine buffer. From what I have seen I suspect it will function fine.
I could always slightly open the gas port if more gas is needed for reliability.
I can see your point about ruining an actual A2 barrel. I built a retro A1 a while back and I wish I would have got an A1 upper before they got expensive. Maybe I need to build myself an A2 or C7 clone.
Hell, I’d love to run a 20" barrel gun if compactness wasn’t such a high priority.
I’ve considered going the route using a pencil barrel with an extended handguard. MI now has a 15" rail that would be perfect for this, but that’s best saved for another discussion.
The obstacle I’ve run into with this lightweight dissipator project everytime I start thinking about it is that it needs to be cost effective while still being a decent improvement over my factory bushmaster dissipator in the weight department. I can get along with the H-bar for most things, but it seems like a lighter version would be much handier.
I appreciate the help you guys have given me and I’ll have to do some more research of my own on the subject of shortening 20" barrels.
Yeah, it’s disappointing how it adds up just to get an extra FSB on a barrel.
If it’s for close it work, you could get your middy turned down, and stick the Magpul Mbus on the rail. They’re not up to par with iron sights, but fine for close work.
I’ve done maybe a dozen of these and have been hands-and-eyes on another dozen.
The logic for not doing it is obvious. I was reluctant to do it at first but had tried it on something of my own and it worked fine. At first I thought I had defied the physics of it all; the guns all worked perfectly. But over time I observed that a few of them were sluggish with certain not-premium ammo, than one or two got finicky with good stuff… I wound up having to fine-tune a few of them; I did open the gas port on one or two.
I would not do it again for a PD and consider it good for the street, even with the opened-up gas port. There are too many variables when you reduce the post-port barrel length by that huge percentage. Yes they work now but I believe the window of function is reduced, the guns will be more sensitive to worn gas rings, dryness, etc. I’d call the mod OK for the guy who is intimate with the inividual gun and can stay on top of maintenance.
Hi
My neighbor has an existing gun. The barrel is around 16" (could be slightly longer, like 16.5 or 17 inches – we put it next to my 16" gun and it looked about the same but since I have a muzzle device was hard to tell exactly). It is probably a cut down HBAR barrel that was then recrowned. It has no muzzle device on it and has a rifle length gas system. He has a pseudo A1 stock on it (cheap feeling with that little hook on the lower back) and says it runs reliably with thousands of rounds down the barrel.
He wants to put it on a new upper (the one he has is some custom 1980s high profile target receiver still in the white aluminum on some custom 1980s machines aluminum receiver) and reconfigure it with a collapsible carbine style stock.
My question, given that it currently has a rifle buffer and spring and tube, what sort of carbine buffer should he be looking at as a replacement?
Thanks
Chad
I just cut a 20" Govt profile barrel to 16" and re-threaded 1/2 28 for a friend. At the recommendation of our range guys who have been shortening our M-16A1’s for years, I opened the gas port to .100 . So far it has worked fine with all ammo tested.
that is something i’ve always wanted to try.
just for fun, i’ed like to build a 605 clone, with the rifle gas.
so, far the project i have going now, is a steve adco, midweight CMMG barrel being milled down to lightweight with gas port moved up to a middy gas,
either way, i dont know why ? i want a 16’’ with rifle gas, but ‘‘just because’’ ???
ha,
peabody
With BCM brining out a light wt mid length with a .625 FSB
I just can’t warm up to the idea of cutting down a perfectly good 20".
Seems to me it would be better to sell the 20" and buy the middie
Gives you everything you want sight radius wise plus well proved
reliability.
My friend’s reasoning and mine has to do with our age and failing eye sight. The farther we can get the front sight away from our tired old eyes the better we can see it. I know we could build a dissipator but decided to give this a try. His gun is still working fine, but has not had a high round count through it yet.
I for one, would love to see a picture of your friends rifle.
i understand perfectly why you went the route you went, i too, getting up there and need those sights as far away as i can get them.
someday ?
i’ve seen on cmmg’s website they have 16’’ barrels with rifle gas, i’ed like to try/build one.
peabody
I will take a photo of it when I see him this next week. The gun was built as a “truck gun.” He did not want any optics, just a simple rifle.
[quote]
yes they work now, but i believe ‘‘the window of function is reduced’’.
the gun’s will be more sensitive to worn gas rings. dryness, etc.
‘‘i’ed call the mod OK for the guy who is intimate with the inividual gun, and can stay on top of it’s maintenance.’’
that is the best discription’and helpfull post i’ve ever read, about cutting down a 20’’ barrel,
for the guy,[like me] who only has two ? three ? AR’s, staying on top of it would be a piece of cake.
alto ? i’ve went the mid-length gas/system on mine, its still one heck of an interesting informational post.
peabody