Built a Hotchkiss Universal SBR

[barnbwt]

Finally completed my first 'tube gun' build. Very simple semi-auto conversion, since this design fired from a closed bolt to start with; just a matter of forcing the disconnector to disconnect the trigger no matter what. Some assorted denial features, two weld seams on a DOM repair pipe section & some milling later...voila!


The four-month ATF wait for the SBR stamp was also 'fast' by their low standards. She just needs testing/debugging, and good coat of paint on the receiver (this kit was something of a beater, so I'm not interested in a full-on restoration or anything)

Super cool design, also super clever, if ultimately a bit impractical. Probably the safest long gun that has ever been made (it has every safety device I've ever heard of apart from a grip safety or decocker --might be why the French passed on it, seeing as their MAS bolt rifle had no safety at all). Ironic given the number of pinch-points on it (though I've managed not to pinch myself so far)

I can go into the conversion/operation details if you really want me to, but I'll just warn you by saying there's about ten moving parts in the trigger group alone.

Test fire scheduled for tomorrow! As heavy as the bolt is, plus the cock-on-opening design, I'm expecting a fairly smooth shooter. Good thing, too; the buttstock is horrible & tiny, the comb is a knurled steel pipe, and the pistol grip is a piece of sheet metal bent into a 'U' open to the front . Oh yeah, the rear sight aperture is about .03" in diameter at the wide elevation

TCB

 

[yugorpk]

That is pretty cool. Where did you get the kit ? I only ask because I MUST HAVE ONE !!!!

 

[barnbwt]

Not many were ever made, only like a thousand or so if I remember correctly. Got this kit on Gunbroker a year or so back with a number of mags. Neat saw cut, 4" constant-area section missing --ah, the good old days.

The Worldguns.ru page actually has a mistake! (rare) The gun definitely fires from a closed bolt, not an open bolt. There is a striker/spring/sear built into the bolt itself, which is released by trigger action when fully forward (acting sort of like a safety sear in that respect, which is funny because the gun also has two other safety sears as well --one automatically-released for automatic fire which also functions as a magazine safety, the other is a trigger-safety which requires the bolt to be fully forward and the trigger to be partially pulled for the trigger to operate)

I've attached some photos from my stamp-submission package; these are the parts before any modification, describing how the automatic fire mode functioned (my letter of intent describes how each step is locked-out by modifications & denials)

If Max wants some more info for the page, I'd be happy to oblige

TCB

 

[horsemen61]

That's so awesome I wish I could do that

 

[USAF_Vet]

Loved this gun ever since I first saw in on Forgotten Weapons. A marvel or nightmare in engineering, probably both. But really cool nonetheless.

Can't wait to see it in action.

 

[barnbwt]

"Loved this gun ever since I first saw in on Forgotten Weapons."
Same here. In fact, that's the video I typically use to introduce folks to the gun building hobby of mine; to a one they've realized off the bat that it's basically a cooler version of antiquing, and not a plot to take over the world.

TCB

 

[barnbwt]

Test fire went awesome, no malfunctions (or automatic fire ). Very rare for a home-built gun to be flawless off the bat, especially one this complicated & heavily modified in the trigger group. Stock/grip horrible-ness was a surprising non-issue, as recoil was incredibly tame. The cock-on-opening design actually functions as a blowback delay (sort of), giving the distinct two-part smooth recoil familiar to roller-delay shooters. For the first time also, I got lucky on the welding of the receiver; thing hits dead-nuts on at 15yds or so, which is about as far as anyone can see through the comically small aperture sights (I can see why literally every description of the gun I've read mentions how small they are)

TCB

 

[Arizona_Mike]

Neat as hell!

Does the ATF have a rule for figuring out OAL with the barrel collapsed or fully extended?

Mike

 

[Carl N. Brown]

^ That is an interesting question.

Folding stock rifle OAL is with the gun in normal firing cindition (stock unfolded).

There are not too many collapsing barrel rifles.

 

[barnbwt]

There are not too many collapsing barrel rifles.

Which is odd, since it's doable on all blowback guns without very much trouble. It's also total movie-cool to shoot the barrel out at the flick of a switch. Didn't seem to impact accuracy too badly, either (at least, not with these sights)

Does the ATF have a rule for figuring out OAL with the barrel collapsed or fully extended?

Only if the shoulder thing that goes up is down, and the clipazine is folded into a barrel shroud.

TCB

 

[Ryanxia]

Very cool. Thanks for sharing.

 

[Dave Markowitz]

One of the coolest builds I've ever seen!

 

[tech9]

TCB, Can you help me? I have a near mint complete saw cut kit only missing about 4 1/2" of tube and want to do EXACTLY what you did. I have the 36mm x 41mm repair section of metric DOM tube but need to know what & how to modify to make a legal semi SBR. If you could walk me thru the steps it would be greatly appreciated. GREAT POST! Thanks in advance.... Ed

 

[CapnMac]

not a plot to take over the world.

Dunno, a world reintroduced to hands-on mechanical skills; an appreciation of engineering, and learning that firearms are not aberrations, but dang fun to shoot? Sign me up for that world

 

[bikeart]

Was fortunate enough to gather a complete kit over a 2 year span and would like to attempt a similar build, my kit was cut cleanly and all parts are there. Were did you source out the replacement tube. do you remember the dimensions (Tube inside and outside measurments) have most of the skills, just have to find the time. thanks

 

[bannockburn]

barnbwt

Probably one of the coolest and obscure (I mean it's a French Hotchkiss for goodness sake), builds I have seen in quite awhile! Even more amazing is that you got it to work first time out! Thanks for sharing.

Oh, and Vive la France!

 

[barnbwt]

Was fortunate enough to gather a complete kit over a 2 year span and would like to attempt a similar build, my kit was cut cleanly and all parts are there. Were did you source out the replacement tube. do you remember the dimensions (Tube inside and outside measurments) have most of the skills, just have to find the time. thanks

If you've got the receiver on the front/back ends still, the center portion has the same outside/inside diameter; very simply repair. You'll also need to run a slot and a shallow flat-bottomed trench down the side with an endmill for the charging handle, and of course cut a hole in the bottom for the trigger group access. The length of the missing section is determined with the lower, whose design allows for a bit of float in that figure. Just make sure the lower isn't squeezed between the front/rear supports, since the trigger safety lever at the front end of the lower will foul on the magwell structure; I left like 1/16" of room at the front to avoid this. Just fit & function check things as you go and it'll be fine.

**Just be sure to install whatever denial schemes you choose to use into the receiver before stitching both ends onto the repair**
***Before anyone asks, I'm not particularly inclined to go very in depth into the actual semi-auto conversion. A) THR frowns on discussion of illegal full-auto conversions (which is a necessary understanding the opposite and making sure it is not readily convertible once completed), B) as a personal one-off item, I was not required to submit for a year-plus formal ATF determination, and I believe my design/modification are more than sufficient, but I do not want to bring attention to my particular method let alone encourage others to follow it or misinterpret it for themselves or ask the ATF about it (and possibly get their/my/others' semi-auto Hotchkiss conversions confiscated). C) It's a fairly advanced technical subject easily misunderstood, especially on this forum, so I'm not comfortable with directing people I don't know from Adam in the subtle art of home dentistry on their rare/valuable artifacts.

TCB, Can you help me? I have a near mint complete saw cut kit only missing about 4 1/2" of tube and want to do EXACTLY what you did. I have the 36mm x 41mm repair section of metric DOM tube but need to know what & how to modify to make a legal semi SBR. If you could walk me thru the steps it would be greatly appreciated. GREAT POST! Thanks in advance.... Ed

I helped out tech9 in PM, but for some reason the new software doesn't tell us when a thread we start gets pinged, or I would have posted that here earlier.

TCB

 

[barnbwt]

barnbwt

Probably one of the coolest and obscure (I mean it's a French Hotchkiss for goodness sake), builds I have seen in quite awhile! Even more amazing is that you got it to work first time out! Thanks for sharing.

Oh, and Vive la France!

To be fair, Hotchkiss deserves most of the credit. This really was a quite simple build, by virtue of it firing from a closed bolt and possessing a semi-auto function from the factory. I am quite proud of how well my first MIG project turned out, though; didn't require that much grinding to make it look decent. Hopefully some other company comes up with a little subgun that works similarly again in the future; that integral striker concept is brilliant in that recoil feels like a roller-locked gun, but with none of the obnoxious locking angles/bolt gap timing issues (or that horrible pawl spring) of the HK design. I recently learned the 1919 belt fed of all things has a very similar striker design as well, so I guess all the servicemen familiar with those will have a better understanding of what I mean.

 

[barnbwt]

Dunno, a world reintroduced to hands-on mechanical skills; an appreciation of engineering, and learning that firearms are not aberrations, but dang fun to shoot? Sign me up for that world

And exposure to really, really, really, reaallllly dumb, arbitrary laws & regulations, as well as oppressive taxation schemes

Gun building is how I learned the true folly of gun control.

TCB

 

[bikeart]

Thanks for answering back so fast - the front receiver section is still attached
think i'll carefully measure (twice) and surgically graft in a section. charging slot and hole in bottom, gotcha - have the end cap too and back section of receiver as i remember?- will be a one off - I will figure out a proper denial before welding system up to be compliant - was not entirely aware of bolt config (closed) before you mentioned it! was too busy admiring the complexity of the bolt assembly and the trigger group. already has a disconnector (thankfully) so one less thing to doctor. thanks for the tips - will let you know - she'll be very rare

 

[barnbwt]

Just exercise some caution with the bolt assembly once you've cocked it; both the cocking lever on the bottom as well as the firing pin will beat the holy hell out of your finger