Building an M4 without NFA: Longer Barrel Carbine or Super-Size Pistol?

[Diamondback]

As previously noted in other threads, I have some weird shoulder-shape problems where I'm unable to properly shoulder a rifle stock. I had the thought that there are two ways to make an M4 NFA-compliant:

1. Longer permanent barrel (whether go to 16" bare, or longer FH and pin-and-weld)
2. Build an "Other Firearm" super-pistol using an SBM4 brace and pistol tube instead of a stock

I'd LIKE to keep an unpinned FH if I can so that as "current issue" configurations evolve I can update the build with them, or can more readily retrofit different cans if by some miracle HPA/similar passes someday. I know that for a typical user the "shoulder pocket" and third point of contact is rather important, but since that third point is unavailable for me and I use kind of a "push-pull" grip where my trigger hand pushes as my support hand pulls on the AFG/VFG/handstop, which option would you follow for a "Current Issue-ish" build?

A. 16" unpinned rifle
B. 14.5" pin-and-weld rifle
C. 14.5" unpinned, no-stock "super-sized pistol"

[Stickman]

As previously noted in other threads, I have some weird shoulder-shape problems where I'm unable to properly shoulder a rifle stock. I had the thought that there are two ways to make an M4 NFA-compliant:

1. Longer permanent barrel (whether go to 16" bare, or longer FH and pin-and-weld)
2. Build an "Other Firearm" super-pistol using an SBM4 brace and pistol tube instead of a stock

I'd LIKE to keep an unpinned FH if I can so that as "current issue" configurations evolve I can update the build with them, or can more readily retrofit different cans if by some miracle HPA/similar passes someday. I know that for a typical user the "shoulder pocket" and third point of contact is rather important, but since that third point is unavailable for me and I use kind of a "push-pull" grip where my trigger hand pushes as my support hand pulls on the AFG/VFG/handstop, which option would you follow for a "Current Issue-ish" build?

A. 16" unpinned rifle
B. 14.5" pin-and-weld rifle
C. 14.5" unpinned, no-stock "super-sized pistol"

Have you thought about a 12.5 barreled "pistol"? It is getting you pretty much the best of all worlds.


If you are set on a "currentish" build, just get a BCM or 6920 and be done.

[Diamondback]

Stick, I have a 12.5 I'm penciling out if I can ever find any documentation to the claim I saw about some West Coast Navy units combining 10.75" URX II's with 12.5" barrels as a "poor man's version" of your unicorn, or if they ever put together another documented 12.5" mil-issue configuration, and a 10.3 pistol modeled after a CASV-based build I'd seen attributed to some USN EOD guys here on the WC that's in Weight/Balance Mockup and concepted as a "Briefcase/Bugout Bag CCW." (Catch is, I got one of the last CASV-ELs Vltor had, and had to make do with Foliage Green--which ended up making for a cohesive "theme" because most of my preferred furniture I used to get huge markdowns on by buying OD rather than black or FDE.) BCM was pretty much going to be the URG builder of choice no matter what path this one took, since I'm one of those "special snowflakes" that likes DIY. :) That said, if a sale on 6920's and my budget find an agreeable meeting place, it was a Short List option too.

Purely unfettered by any "lookalike" requirement, I'm also toying with the idea of combining a LAW sidefolder/A5 buffer/SBM4 brace and a Dolos takedown front end for a "Quick Change" briefcase-carry setup that with interchangeable barrel/HG's could go from PDW/Active Shooter Response to Patrol Carbine or maybe even limited Countersniper in a matter of seconds just by swapping front halves. Problem is, if the optic for longer-range can't reliably hold zero between detach/reattach I think this one's just another visit from the Good Idea Fairy...

[Jammer Six]

I live where you live, I've done some reading and asked stupid questions from folks here in Seattle.

I concluded that there's no way to legally buy an M4 (meaning a selective fire weapon) in Washington State. I concluded that if I wanted to own any selective fire weapon, I'd have to move to Idaho.

[Diamondback]

Jammer, omitted from mention was the implied deletion of Select Fire--"as close as possible while staying Title I."

[Renegade04]

A. 16" unpinned rifle - If you plan on getting a suppressor anytime in the near future

B. 14.5" pin-and-weld rifle - If there is no plan on getting a suppressor for it. If you are waiting on the HPA to pass, it may be some time before that ever happens, especially since the Democrats will control the House.

I would not mess around building a pistol, especially since your only intention, by admission, it to only shoulder-fire it. There is a wide assortment of stocks that were used on the M4s in service and any one of those may yield one that is more comfortable for you to shoulder.

[RHINOWSO]

If you are waiting on the HPA to pass

Who believes that these days? If someone does, please tell me what they are smoking, because I'd like some of that.

[Diamondback]

I would not mess around building a pistol, especially since your only intention, by admission, it to only shoulder-fire it. There is a wide assortment of stocks that were used on the M4s in service and any one of those may yield one that is more comfortable for you to shoulder.

Renegade, I have no intention of shouldering this thing or any other long-ish arm, because as I said previously I'm physically UNABLE to do so--my usual technique has stocks or braces ratcheted down as short as possible, either just "floating in space" with no shoulder contact or more commonly tucked into my elbow joint. (Best comparison is something akin to how you'd hold a Chicago Typewriter if you were bringing it up to use the sights rather than spray-and-pray.) Sounds odd, looks chicken-wing odd, but so far works for me where more conventional options don't. "Improvise, Adapt, Overcome," right?

[Renegade04]

Renegade, I have no intention of shouldering this thing or any other long-ish arm, because as I said previously I'm physically UNABLE to do so--my usual technique has stocks or braces ratcheted down as short as possible, either just "floating in space" with no shoulder contact or more commonly tucked into my elbow joint. (Best comparison is something akin to how you'd hold a Chicago Typewriter if you were bringing it up to use the sights rather than spray-and-pray.) Sounds odd, looks chicken-wing odd, but so far works for me where more conventional options don't. "Improvise, Adapt, Overcome," right?

Gotcha. That does place you in an awkward predicament. I do not know that a brace will be any better for you than a stock in that case. The only deciding factor for you would be the barrel length in that a brace, as much as I hate them, would allow you to run pistol build with a 14.5" barreled upper without having to pin and weld the FH.

[Diamondback]

TBH, most of the use I get from Rear-End Furniture is as tail-weight to help improve balance, something I figured out while handling an 07/SOT friend's TSMG's. Sometimes as a carrier for spare mags, but mostly as ballast. The stubby little arms (I'm 5'6", IIRC around like a 9-10" LOP) don't help much either, LOL.

OTOH, if I stick to pin-weld or 16" w/stock, that allows flexibility so that others in the household can use it if needed rather than being as primary-user-specific as the "briefcase special" project. 6920OEM1 has a certain "keep it simple" appeal as a starting point... and since this is planned as one half a His/Hers set, it would probably be a good idea to ensure that either of use can use either iron in case one breaks while on the range.

[Renegade04]

TBH, most of the use I get from Rear-End Furniture is as tail-weight to help improve balance, something I figured out while handling an 07/SOT friend's TSMG's. Sometimes as a carrier for spare mags, but mostly as ballast. The stubby little arms (I'm 5'6", IIRC around like a 9-10" LOP) don't help much either, LOL.

OTOH, if I stick to pin-weld or 16" w/stock, that allows flexibility so that others in the household can use it if needed rather than being as primary-user-specific as the "briefcase special" project. 6920OEM1 has a certain "keep it simple" appeal as a starting point... and since this is planned as one half a His/Hers set, it would probably be a good idea to ensure that either of use can use either iron in case one breaks while on the range.

I, too, am 5'6". I do not have any issues with any stocks, even the A2. As far as your dilemma, you may want to go ahead and get a 16" with a stock for family use. It would be much simpler. AS far as a user-friendly stock that will suit your situation, that will be trial and error for the most part. You will need something you can attach some sort of ballast for when you shoot.

[Diamondback]

I, too, am 5'6". I do not have any issues with any stocks, even the A2. As far as your dilemma, you may want to go ahead and get a 16" with a stock for family use. It would be much simpler. AS far as a user-friendly stock that will suit your situation, that will be trial and error for the most part. You will need something you can attach some sort of ballast for when you shoot.

Right now my "heavyweight" carbine uses a FAB Defense mag-carrier stock with their monopod recoil pad, based on something an old wargaming buddy who was IDF had his armorer rig for one of his guys about our size though the full-length free-float adds a ton of front weight. The briefcase rig has an SBM4 with a 40-round PMAG stuck in its tunnel as a ready reload (not live, this is an ergonomics test rig on an unmachined 80% at this point), and I bet for any build some saddlebag-style carriers with extra mags would be expedient ballast with a useful emergency role rather than just "weight for sake of weight." The other thing that doesn't help is the combo of "never lost the baby fat" and seemingly never having grown any pecs--something I admittedly need to start at least cranking out some pushups every morning and otherwise working on so that even if I'll never measure up by Will Brink standards I can at least maybe have something up my sleeve you wouldn't expect from "just another tub o' lard." If I go rifle, thinking either the basic M4 waffle with an added recoil pad or a SOPMOD, trying to match the "Marine Corps Annual Rifle Training" specified config in general look and layout--right now I'm thinking writeoff cans, go BCM pin/weld 14.5 with stretched A2 on a Colt or BCM lower and if a miracle happens I can always have the A2 cut off and replacement pinned later.

Some comparative numbers on potential users...
Me: late 30's, 5'6, 225lb.
Mom and aunt: both 60's, each 5-2 to 5-3, 320-340lb. (we're working on trying to trim mom down, get her out of the early stages of morbid obesity-induced congestive heart failure but it's a long slow process)
Girlfriend: mid 40's, 5-8 to 5-9, around 160

[Renegade04]

If you are "trying to match the "Marine Corps Annual Rifle Training" specified config in general look and layout", then I say the "go-to" stock would be the M4 waffle stock (Gen 4) and add a recoil pad. As you say, if you write off the suppressor, a 14.5" barrel with a pinned and welded extended A2 FH (I prefer the one from BCM). Windham Weaponry does offer a 14.5" M4 upper assembly with a pinned and welded extended A2 FH. It appears to come with a M16 type BCG and charging handle as well as a detachable carrying handle.

https://shop.windhamweaponry.com/collections/upper-receiver-assemblies/products/ur14m4-7fha4b

Midway has a recoil pad for the M4 stock.

https://www.midwayusa.com/product/1003265259/promag-recoil-pad-slip-over-ar-15-carbine-6-position-stock-us-stamped-rubber-black