Another scratch build; Ultralight folding .22 semi-auto.

[MachIVshooter]

So, while I await more powerful hammer springs from Wolff (Which they have been absolutely exemplary about helping me with, BTW!) for my O/U pistol build, I decided to start my next project. The idea is a semi-auto .22 rifle that folds in the same fashion as a Kel-Tec Sub-2000, has a folded length of just 16-1/4", and weighs in at or under 2 lbs.

The barrel is a chambered .22 LR "liner" from an eBay seller I've had good luck with in the past. As received, it wasn't perfectly true, but nothing I couldn't fix with the lathe, a dial indicator and a little bit of manual force. Got it trued within 0.002", cut it to 16.25" and recrowned, and threaded the chamber end 3/8-40.

My plans for bolt and receiver aren't fully finished, but the barrel block prints were, and I was anxious to cut metal, so I started there. The receiver block is 7075-T651 Aluminum, but the barrel actually threads into a .600" diameter piece of 0-1 that is pressed into a .5985" hole in the block:



The hinge is a .188" radius on top, with a centered hole that is reamed to .1880". The lower "ears" have a centered hole reamed to .1250", which will be the pivot pin for a spring loaded latch that secures the barrel assembly when in the unfolded and locked position.



Barrel threads in flush to the rear of the block



And the handguard, a 13.25" piece of 23x25mm carbon fiber tube, is pressed onto the barrel block



Current weight of the barrel block, barrel and handguard assembly is 9.9 ounces. There will be an aluminum front sight/handguard cap piece that will increase that weight by ~3/4 ounce.

The receiver will also be 7075-T651, the bolt itself 416 stainless with a starting weight of 6 ounces. Stock I'm not fully decided on, but if it doesn't look too goofy, I'll probably use more of the 23x25mm CF with a UHMWPE shoulder piece.

Will update as I have them!

 

[barnbwt]

Sweet.

That is all

TCB

 

[WestKentucky]

All this...self taught...with a freaking mini-mill.

I would love to see a thread showing us your equipment and shop setup. It would tie your micro-AR, shothandgun, and this minimalist rifle together really well. Would that be on topic in gunsmithing?

 

[WestKentucky]

So what's the plan for the reciever? Simple striker or are you doing something fancy and fun?

 

[WestKentucky]

I'm going to suggest this, expecting it to be heavily criticised...almost every 22 fail to fire I have ever seen was solved by turning the shell and letting the striker hit elsewhere on the rim. If you do a 2 pin hit it would take more oomph to get the strike force required, but it would greatly reduce the chance of snapping on a dead spot.

 

[thewillweeks]

I'm going to suggest this, expecting it to be heavily criticised...almost every 22 fail to fire I have ever seen was solved by turning the shell and letting the striker hit elsewhere on the rim. If you do a 2 pin hit it would take more oomph to get the strike force required, but it would greatly reduce the chance of snapping on a dead spot.

I've always thought this myself, might be something worth looking in to.

 

[MachIVshooter]

I'm going to suggest this, expecting it to be heavily criticised...almost every 22 fail to fire I have ever seen was solved by turning the shell and letting the striker hit elsewhere on the rim. If you do a 2 pin hit it would take more oomph to get the strike force required, but it would greatly reduce the chance of snapping on a dead spot.

Actually, I'm still considering an open bolt firing system with that sort of face; basically a flat screwdriver blade in a circle. The open bolt system would allow the used of a lighter bolt as well, and simplifies the fire control system. Lighter bolt + fewer fire control parts= lighter overall weight. Not building a target rifle here, especially with the 3/8" diameter barrel, so the accuracy loss of open bolt is negligible.

I would love to see a thread showing us your equipment and shop setup. It would tie your micro-AR, shothandgun, and this minimalist rifle together really well.

Lagun FTV-2; X & Y axis DRO, Clamp on 90° R8 head, Palmgran 6" vise, Troyke DMT-12 compound cross slide rotary table, Vertex BS-0 dividing head, 5C rotary indexer + 5C 4-jaw, another 4" rotary table, 2" tool makers vise, etc.



Hardinge HCT; X axis DRO, 5C spindle, 9" Buck 3 jaw, 5" Hardinge 4 jaw:



I've dropped a lot of money the last couple of years after trading into the mill and lathe. Also accumulated probably 400 different end mills, face mills, dovetail cutters, keyslot cutters, and constantly adding/replacing. eBay auctions are a great way to score new & used cutter lots on the cheap, but it's still expensive as a hobby. I'm finally starting to get some paying jobs here and there, though.

I still have my mini mill, too, use it for a lot of drilling and secondary ops. Comes in handy with the tilt-swivel vise when I need to bevel a corner or bore holes at compound angles; much faster to use the mini than set up on the big one if I don't need to hold <0.003".

 

[MachIVshooter]

Oh, forgot to mention for those who are curious. I hate making magazines, especially since one usually wants several on hand. As such, I try to use existing, proven magazines. Since Remington 597 magazines are lightweight (0.7 ounces empty), compact, plentiful and relatively cheap, and since I have some already, that's what this will use.

 

[WestKentucky]

You sir have an incredible shop at your disposal. I am envious. Im not sure that open bolt will fly, it might, but I'm getting the not-so-warm-fuzzies about a weapon firing from open bolt and the ATF not being real happy. If your feeding it from a magazine then that could look to a bystander with a badge to be a machine gun being built. I would advise against it and would suggest almost anything else, probably for simplicity and weight I would think a really simple bolt action. To completely enclose it and protect the insides, you could consider a thumb trigger under a Maglite switch cover. Simple, lightweight, different.

 

[HB]

I agree with the above poster. I'm not too knowledgable about NFA items tho. I've never thought of the "2 pin" firing pin but that coupled with with a bolt action would be very unique.

 

[MachIVshooter]

Open bolt semi-autos are perfectly legal, provided that they're manufactured in such a way that they are not "readily converted" to fire full auto. Simply put, it means designing your fire control so that removal or modification of existing parts does not create a MG. To do this, you simply make the linkage between trigger and sear an integral disconnector that renders the weapon inoperable if altered, damaged or removed. Really quite easy to accomplish by making the link/disconnector in such a way that grinding off the portion which the bolt engages to disconnect it would cause the linkage to fall away entirely, leaving a dead trigger.

Furthermore, as this firearm is designed from inception to be a semi-auto, and as it is entirely hand made (no "readily available" parts for FA conversion), it cannot be considered a MG. Of course I have the capability of making it (or any other) semi-auto a machine gun, but I do not have the intent, nor have I (or will I) manufacture parts for such.

 

[bannockburn]

And so another "build form scratch" adventure begins! Looking forward to the next installment.

 

[bainter1212]

Tagged. In for this one.

 

[LoneGoose]

You are certainly living a life that most of us only dream about. "If you can think of it, it can be done." My hat's off to you.

 

[barnbwt]

Open bolt semi-autos are perfectly legal, provided that they're manufactured in such a way that they are not "readily converted" to fire full auto.

I would highly, highly, highly (highly) recommend starting a thread in one or more technical forums before proceeding. Don't take my word for it, since you don't know me from Adam. The responses will be overwhelmingly against your plan, from folks of all walks of experience. The ATF has made it abundantly clear that the bolt or carrier may have no role whatsoever in releasing the striking mechanism or striking the primer themselves. The standard test they perform involves removing the sear parts and releasing the bolt, to see if it will run as a 'stutter gun' until empty. Even though these devices have no trigger/sear, the ATF holds they managed to "fire more than one shot per pull of the trigger."

I do not think it is possible to construct an open bolt action that cannot be easily (and reversibly, which is the most concerning from the ATF's perspective as prosecutors) converted to full auto fire. There are many variations, I'm simply not aware of any getting approval (not even single-shot rifles with no magazines, believe it or not). Oddly enough, if you'd made your design and registered it prior to the moratorium in the late 80's (or was it early 90's?) they'd be perfectly cool with you rocking the exact same device (even though you never paid the transfer tax for what they now call a 'machinegun' )

Maybe it's possible, but you are boldly tacking into uncharted waters marked "HERE THAR BE MONSTERS" in blood...

TCB

 

[MachIVshooter]

The standard test they perform involves removing the sear parts and releasing the bolt, to see if it will run as a 'stutter gun' until empty. Even though these devices have no trigger/sear, the ATF holds they managed to "fire more than one shot per pull of the trigger."

I had been under the impression that the test involved removing or altering the disconnector. Hard to argue more than one round per one pull of the trigger if the trigger has been removed or is non-functional. The design I have sketched would render the trigger dead and the sear locked if the disco is removed or altered, as the disconnector is the connector as well.

My understanding was that the ruling on the open bolt guns in question was made because they were full auto designs modified for semi-auto function, which were easily restored to full auto. Ergo, a completely custom design for which entirely new parts would have to be made to make it fire more than one shot per trigger pull is not in the same category.

I will do further research on that ruling, as I have admittedly only a cursory understanding of it, and had never contemplated an open bolt until now. The negative effects on accuracy and trigger pull have always been a detractor, but for the purpose of this build, the lighter weight and simplicity of the design appeal.

ETA:

Unless I'm mistaken, the relevant rulings are ATF 82-2, 82-8 and 83-5, which all have this common language:

The trip lever (disconnector) is designed in such a way that a simple modification to it, such as bending, breaking or cutting allows the
weapon to operate automatically.

The disconnector is designed in the KG-9 pistol in such a way that a simple modification to it, such as cutting,
filing, or grinding, allows the pistol to operate automatically.

The disconnector and trip are designed in the SM10 and SM11A1 pistols and in the SAC carbine (firearms)
in such a way that a simple modification to them, such as cutting, filing, or grinding, allows the firearms
to operate automatically.

 

[jmorris]

I would call the NFA branch before building it 304-616-4500 and talk to them and if they say it's OK get it in writing too.

I think it could be possible to make an open bolt gun that would be hard to convert to FA but any design where one could just pull the bolt back and let it go until empty, with a gutted trigger group likely would not fly with them but you can ask.

They might also tell you to send in a "sample" for them to examine but I would get the proper FFL and SOT first, just in case they decide it's a machine gun, with the right stuff you still would not have broken any laws.

I seem to recall a few years before they shut the machine gun registry down in '86 they decided all open bolt semi's were "readily convertible" but grandfathered the old ones.

looks like the open bolt ban was in 1982.

 

[MachIVshooter]

I seem to recall a few years before they shut the machine gun registry down in '86 they decided all open bolt semi's were "readily convertible" but grandfathered the old ones.

As far as I've been able to determine, there's not a real clear answer beyond the post-'82 (and '83) banning of those 3 specific models. It seems that their stance is "we don't like 'em, and we'll scrutinize them", to which the industry simply said screw it, we'll just build closed bolt designs only. But there are quite a few home builds with open bolts, and as far as I can tell, it's not the open bolt operation itself that makes them a no-no, but features of the design that would make them "readily convertible", per the actual language of NFA. Further, I would guess that the more complex parts of a design that precludes easy conversion makes it impractical to build them on a large scale anyway. Combine that with the reduced accuracy and poor trigger pull characteristics of open bolt, and there's little use for them outside of very specific applications-namely weight savings.

For this build, I've decided I don't want to wait on FTB, so I will proceed with a closed bolt design. However, I do intend to submit a schematic of my proposed "non-convertible" open bolt system, which I will use in future builds if they OK it. The advanced ignition of open bolt allowing for a significantly lighter bolt assembly on a blow back gun definitely has appeal in certain applications.

 

[jmorris]

The term "trigger" is generally held to be the part of a firearm that is used to initiate the firing sequence

Page 168 here, https://www.atf.gov/firearms/docs/atf-national-firearms-act-handbook-appendix-b/download

So if the bolt could operate in the absence of trigger components the lever you use to cock it would become the trigger.

That said any regular closed bolt semi could be converted to operate FA in that manner with anything that would make the firing pin protrude even in the absence of a hammer strike. No one ever said there laws and interpretations make sense.

 

[MachIVshooter]

Well, I think I have a pretty simple, workable closed bolt receiver & action design sketched up, just have lots of dimensioning to do now. The sketch shows the sear in a notch on the striker that won't actually exist; it's just easier for me to draw it that way for locating pins, springs, safety, etc.

And sorry for the old school pencil & paper approach. I know many are used to seeing the spiffy CAD designs, but I hate CAD. The cheap programs are very limited, and I'm not gonna spend the money for Solidworks or similar until I have a VMC with which to use CAD/CAM.

The recoil spring is actually a bit smaller than the .750 bore and bolt OD, so while it looks in my sketch like the spring will interfere with my connector, remember that this is just a sketch, not a blueprint, so those little details are not that accurately represented. The connector pivots on a pin in the trigger, and the connector spring will also serve as the trigger spring. When the bolt travels rearward, it pushes the connector out of the notch on the sear, allowing the sear to return home and not re-engaging the sear until the trigger is released, allowing it to fall back down and snap forward into the notch.

The striker will actually be longer than the receiver, protruding out the back and into the stock tube. The forward portion where I show shading will be a radiused transition into a 1/16" blade, keeping the orientation correct. The extractor is not represented in the sketch, but will be a simple spring loaded hook extractor. The striker will serve as the ejector.

The bolt is completely cylindrical, kept properly oriented by the sear.

The safety is AR-style, but obviously located very differently. When the lever is perpendicular to the bore, the sear is blocked from movement in the same fashion that the AR's trigger is. Rotated forward (probably 90°. but I'm not quite decided yet), it allows the sear to drop.

And yes, it will use AR grips. Just makes sense these days.

 

[chicharrones]

It looks promising, MIV!

What influences from other guns (if any) have inspired this creation?

 

[Bobson]

These threads are awesome. Great job, lookin forward to more.

 

[MachIVshooter]

What influences from other guns (if any) have inspired this creation?

Well, the folding back over the top is basically like a Kel-Tec sub-2000. The long firing pin protruding through the rear of the bolt with a spring that assists the recoil spring is similar to the Remington 522 Viper. Magazines are Remington 597. Safety is AR type, although located elsewhere and acting on the sear rather than trigger. Aside from that, it's a basic idea I had in my head that is evolving as I go.

Wasn't originally going to do an AR grip, but in order to make use of the rest of the 25mm carbon fiber tube I have as a stock tube, it's gonna be a straight line configuration like the AR, so that necessitates a protruding pistol grip. The receiver really just took shape today in that sketch, didn't know exactly how I wanted to do it prior. Initially I wasn't even sure I wanted to do semi-auto, as a bolt action with a titanium bolt would be lighter. But the weight penalty for an autoloader isn't that much; I think I can still hit my target weight even with a 6 ounce bolt, which I made tonight, along with the firing pin:





Firing pin I may revisit, I'm not real happy with the way it turned out cutting it from a Craftsman #3 phillips screwdriver. Gonna need a longer 5/16" spring, too. I still need to decide how I'm doing the extractor, but I'm leaning toward a spring steel claw that is retained by a screw in bolt knob.

Cutting the receiver is gonna be a little tricky, need to order a .750" reamer with 6" flutes to do the bolt bore. As it will also be monolithic, the slot for fire control parts is going to be cut through the trigger guard with an extra long 1/4" end mill.

 

[jmorris]

Cutting the receiver is gonna be a little tricky, need to order a .750" reamer with 6" flutes to do the bolt bore.

You should look inside an AR7 receiver some time, I think they just used a dull drill for the "bore".

 

[barnbwt]

Mach has higher standards