mg42 pistol build?

[panaceabeachbum]

First off I want to start by stating this is just a thought process spawned by to much spare time, nothing more.
looking back thru old issues of machinegun news I see adds for all sorts of neat pistols , probably the least practical but neatest is an hk21k beltfed .308 witha 4" bbl. Its an hk21 blet fed cut down to mp5 k size, so the wheels started spinning on thoughts of a semi 42 pistol (mostly sparked by this 922r thing). I think if a person started with a set of the brp rear rec flats there could be no confusion on it ever having been a rifle so I assume like the ar and ak pistol builds it would be legal to build with pistol length bbl. I notice the ar pistols still seem to use a buffer tube of standard thread size, so it would be possible someone with ill intenet could unscrew the pistol buffer tube an install a riffle buffer tube and stock. The 42 pistol would still need its buffer and it would be easy to machine away the external threads so a riffle buttstock could not be attached. Do you think it would be neccesary to prevent a rifle buffer from bieng introduced entirely? Best method? maybe machine away .10 from locking face on pistol buffer and making buffer tabs of proper length to prevent unmodified buffer? I think starting with a virgin rec and preventing attachment of a standard 42 buffer/stock assembly would allow the legal build of a pistol. I have a set of the unwelded flats, and already have pistol versions of hk91, fal, ar, am180, krink, and looking for the next silly project. Just thinking aloud here, any thoughts?

[Arsenal]

(also thinking out loud)


you may be on to something - IIRC there is an ATF letter out there authorizing attachment of an AR15 collapsible stock tube to be used as a buffer tube on an AR based pistol.

The letter stated that the CAR stock tube could be used UN-modified and was legal, no problems unless an actual stock was attached (thus creating an NFA- SBR)


There shouldn't be any reason the -42 wouldn't be similar, discounting of course that ATF has already contradicted other rulings when taking the -42 into account.

[panaceabeachbum]

I just pulled my old hk51 pistol fromn volmer out to compare to the new vector 53 pistol. My volmer 51 has the same tabs welded on the side as the sp89 to prevent a rifle stock from bieng attached but the new vector 53 pistol has nothing (other than common sense) to keep someone from sliding a rifle stock in place. seriously considering an SA42 pistol build.

[KMFDM]

It would probably take a bit of time to figure out because you would have to probably re-design the whole buffer/recuperator and recoil spring assemblies respectively. Because of it's recoil (short) operation you might run into other issues like cycling and bolt speed. Then having a short barrel and a booster assy would probaly be quite uncomfortable to shoot with excessive muzzleblast. Let alone recoil would probaly be quite punishing because of pressures at the end of the shorter muzzle, lighter barrel and increased speed of operation and short recoil design. Probably like shooting an old browning auto-5 without the stock (Yes, I am aware it is a long recoil system and the buffer/bolt assy return spring protrudes into the stock-but it used as an concept.) I would guess that by the time you ended up with a usable system it would be very darn difficult to actuate the cocking handle and an ungainly beast. You also would have to tune the booster, flashider ports and exit holes also they would probably need to be strengthened. Probably also the locking wedge in the bolt would need a bit of modification also? It may need a new angle ground into it to ensure proper timing of the system. Weight of the system I would guess would be in the 10# range or so. You would have to get the heaviest bolt you could find would be my guess the old 750gm bolt assy. would probably needed.

The MG42 is regulated to operate at muzzle pressures of about 4000psi: now cut the barrel down to about 7" substantially reducing the weight of the recoiling masses in the process and increase operant pressures to about 30,000psi at the muzzle it would make for a lot of work and a not very durable system that is subject to short cycling/jamming because of lack of a proper support (no shoulder stock) of the mass that recoils.

An HK 21 uses delayed blowback with rollers and you can more easily set the gun to operate with a short barrel than a recoil operated gun. The HK21 is not that good of a system compared to a proper machinegun either-lots of gee-whiz but they eat up parts right and left in my experience.

But one never knows maybe it would work? But you would have alot of obstacles to overcome methinks. I think you would have exceeded the design limitations of the system at that point. I would think it would literally beat itself to pieces in short order.

[TOM R]

this is an interesting idea a few guys have been kisking around but my only problem is i am not to shure about how safe it is with your hand that close the the bottom eject area if there was an out of batt explosion, I think nomatter how light you could make this it would still need a foregrip that would be near that lower ejection hole, just my .02

[panaceabeachbum]

I was thinking the much lighter recoiling mass of the short bbl might cause some problems but I wonder if the booster or cup might be reamed substantialy larger , reducing the amout of gas bearing on the bbl bushing and slowing the whole thing down. The lack of the rigid hold the stock provides is a very good point. I notice one of my full size sa42's tends to short stroke on the soft mount but runs 100% reliable against the shoulder when fired off the bipod ,you're right probably have the same problem with the pistol . In reality this thing like my other 42's would be fired off a ground mount 99% of the time, this whole rifle/922r thing is what started this thought process. I am sure the muzzle blast would be violent but I am used to it shooting my 8" bbl hk .308 and 4" bbl .308 fal pistol. I have a friend with a 10" .50bmg pistol, feels like its breathing for you on every shot.
Tom you bring up the most important point, safety. I have fired aprox 3k rds thru my two sa42's and I still dont shoot off the shoulder or hip as I cant bring myself to extend my hand up past that chamber area

[Pirate]

Other than doing some mods to prevent installation of a stock, I think it would work fine with out any other changes. I have a g3 pistol and several ak pistols and having a belt fed one would be cool.

[panaceabeachbum]

Maybe thats the best way to go. One of my friends thats a non posting member is in a wheel chair and shoots his from the soft mount only, and doesnt even own a buttstock. with the whole 922r thing poping up this might allow builds sans the buttstock as a pistol.

[panaceabeachbum]

decided on 16 3/4" for my pistol bbl, cut a shroud down by a distance equal to 2 of the oblong slots. Will reweld shroud and begin welding the two BRP rec halves together tommorow.

[salt6]

You will need to take into account the bearing surfaces on the muzzle of barrel.

[drooling idiot]

decided on 16 3/4" for my pistol bbl,

16 3/4 " long barrel qualifies as a rifle barrel you MUST be under 16 " on the barrel AND 26 " OA length to be a pistol.

more research before YOU qualify for a club fed vacation

[panaceabeachbum]

decided on 16 3/4" for my pistol bbl,

16 3/4 " long barrel qualifies as a rifle barrel you MUST be under 16 " on the barrel AND 26 " OA length to be a pistol.

more research before YOU qualify for a club fed vacation

I dont think this would qaulify for a vacation in club fed, but might be considered a rifle , but as long as it meets 922r it should be legal wether I choose to afix a buttstock or not. I definitly dont want to break any laws, can you point that reg out in ATF the big book, section and paragraph#?
I know there is a min bbl length on rifles but I did not know there was a maximum bbl length on pistols or any limitations on length. I do see it has to have a vertical grip that extends down conspicousley from the bottom and has to have an overall hieght exceeding 3 3/4" to be a pistol but I dont see the max bbl and overall length.
Since I am at an overall of aprox 32" and 16 3/4 bbl Ill just call this a rifle as i would like the ability to afix the buttstock anyway. I have a US made rec , fcg and trig housing so I think I am OK on 922r foriegn made parts count, but would like to be sure. Still a little unsure on the booster/flashhider.
Here is a pic of todays progress, this is a rec from the right and left stampings and ratchet plate from BRP , and a shroud and other parts from one of the M53 yugo sets. Should get rails riveted in and gripstick mount in place tommorow.

[drooling idiot]

i think this is what i was thinking of....

(4) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length;

TITLE 26 > Subtitle E > CHAPTER 53 > Subchapter B > PART I > § 5845 Definitions

not really so much about what qualifies as a pistol so much as what requires a tax stamp.

and

(8) The term “short-barreled rifle” means a rifle having one or more barrels less than sixteen inches in length and any weapon made from a rifle (whether by alteration, modification, or otherwise) if such weapon, as modified, has an overall length of less than twenty-six inches.

TITLE 18 > PART I > CHAPTER 44 > § 921 Definitions

which doesn't state directly what is a pistol but is used to define a pistol indirectly by the BATFE.

could you make the argument your not making this "pistol" from a rifle so the law doesn't apply ....??
I think its better to ask and get a determination before you just decide to call it a pistol .
It seems to be more a 922R compliant belt-feed carbine than a pistol.

[panaceabeachbum]

gotcha, since this would begin with a parts set and a newly made virgin rec ( never assembled stampings from BRP) I think it would be easy to prove a pistol just the same as a g3 ak or ar pistol, but Im going to take your advice and and just go with a carbine build. The picsa dont really reflect it but this thing is short!

[MEGALODON]

Panacea, how's this project coming along?

[panaceabeachbum]

I finished up the carbine build within a few days of starting this thread, shoots great. Decided not to pursue the pistol build currently

[MEGALODON]

Did you have to modify the booster? and if so, to what size? How did you deal with the end of the barrel where it locks up? Did you have to make any other special modifications? thanks.

[striker754]

state law plays into the definition of a rifle and pistol too.

If you are doing a reweld, it becomes a shady area. US code says made and remade from a rifle. While a reweld is not technically a rifle, it once was. Complicated stuff.

[drooling idiot]

well technically it never was a rifle it was a machinegun