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

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What is the stroke length of the bolt?
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2 inches.

I bored the receiver a little deeper yesterday and made a tail that is threaded to the rear bolt, worth 3/4 ounce. Fired 4 more times with HV, only one successful ejection (better than none). But I only tried it with the 5/8" x 2.5" .055" wire spring. I have a 5/8 spring I made out of .039", which is a bit soft, but we'll give it a shot later. I just ordered some .045" wire to split the difference, though.

Regardless, I still have to redo the bolt for feeding. Everything I've done has brought it closer, but even if it wasn't catching empties, the number of times a round properly chambers with full bolt speed is less than 1 in 10. It would feed fine with manual action, but just too violent with an autoloader.
 
Much overdue update. Granted, I have had a crazy busy summer, so haven't had a lot of time, but we're finally very nearly done here.

One thing I had done over the last couple months was make a bolt out of 360 brass, both because it adds a little weight, and because it's easier to work with for prototyping. Got the feeding issue sorted with that, but it was still failing to eject more often than not. I resigned myself to making an ejector, but due to the aforementioned craziness, the rifle got shelved until this last weekend.

I finally got back to it, settled on a fixed ejector mounted opposite the extractor using two #2-56 flat head allen screws from the outside. I opted to cut it from titanium, not so much for weight savings, but because I didn't feel like heat treating the thing, and 6/4 is already plenty strong in the annealed state. With that, we solved the ejection problem, but began running into an issue with feeding and striker reset. Went to a lighter recoil spring, and that largely fixed the resetting issue, but was underpowered for reliable feeding. Ugh.

Yesterday I was very motivated, and got the final edition of the bolt cut from S7 steel. With the lighter 0.035" spring, bolt speed was too high and forward force still insufficient for feeding. So I decided to try the .045" spring again with the slightly lighter steel bolt, and viola! We had feeding and ejection. Still had issues with striker reset, but cutting the sear notch a little further back and giving it a slight angle did the trick! I'm getting a few light strikes, but that's nothing I can't resolve with a slightly heavier striker spring than the 0.025" wire I used for the current one.

The ejector:

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Yes, the striker is canted slightly. The bolt rotated just a hair in the vise, and I didn't notice it until I started cutting. No matter, it doesn't affect function, and I didn't feel like remaking the thing over that (one of the last steps, just before extractor groove and pin)

The rifle has close to 1,500 rounds through it now in testing, so I think we can safely say that the design is sound. It just took a bit of tweaking and tuning this brand new design to make it run.

Now on to making sights and buttstock, a couple other minor tweaks, then cerakote and done!

Will try to get a decent video of firing soon.
 
I like the feed ramp integral with the barrel assembly similar to the Ruger pistol barrel. Good solution to a common problem, but not the easiest.

The sheet metal tab feed ramp on the ArmaLite AR-7 magazine is fragile and easy to get out of align, especially as the mag catch wears. That's a weakness on the AR-7 design if you are not inclined to do maintenance checks (and tweaks) on the magazines.
 
I like the feed ramp integral with the barrel assembly similar to the Ruger pistol barrel. Good solution to a common problem, but not the easiest.
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No, it's not the easiest, but the only practical method for a folding rifle in which the bolt comes out the front of the receiver. There was just no good way to attach a feed ramp to the receiver without compromising integrity.

The sheet metal tab feed ramp on the ArmaLite AR-7 magazine is fragile and easy to get out of align, especially as the mag catch wears. That's a weakness on the AR-7 design if you are not inclined to do maintenance checks (and tweaks) on the magazines.
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Are you just stating in general? I'm using modified Remington 597 mags. My original pattern used unmodified, but feed problems required the magazines seat higher. I deciding modding mags was preferable to making another receiver ;)

We'll get around to a better video, but here's a low res teaser in the shop with my bucket-O-sand

 
I just like idea of the feed ramp integral with the barrel, rather than part pf the receiver aligned with the barrel, or part of the magazine. In part because it has worked well for me in my Ruger MkII for the past 30 years or so.

And on your folding barrel design, the ramp on the barrel fitting a slot in the receiver serves as an alignment tab. That might be an accident of design but it seems to me to be a good feature to be kept for a folding barrel design in addition to the hinge and catch.

(I have been fascinated by wilderness survival guns as a practical sub-group of firearms for fifty years or so, and find your gun interesting.)

Added: (Watching that testfire video, I feel the enthusiasm expressed by Dr. Frankensten: "It's alive! It's alive! It's alive!")
 
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And on your folding barrel design, the ramp on the barrel fitting a slot in the receiver serves as an alignment tab. That might be an accident of design but it seems to me to be a good feature to be kept for a folding barrel design in addition to the hinge and catch.
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I've got pretty tight tolerances on the hinge, and the beveled ears are what really lock it down. There's some clearance in that slot, being about 0.015" wider than the ramp, so it doesn't do much to hold alignment.

Added: (Watching that testfire video, I feel the enthusiasm expressed by Dr. Frankensten: "It's alive! It's alive! It's alive!")
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Very much so for me. Lol. Hundreds of rounds fired 1, 2, sometimes 4 or 5 in a row, but only just tonight being able to load and empty a magazine reliably.

I am going to make custom baseplates for these mags, as an OOB firing with the lighter recoil spring did damage the plastic one, and it'd look better with aluminum anyway! I will probably mod one or two of my 22 or 30 round mags for this critter. They'd still function in my 597 VTR, but wouldn't seat tightly without making a spacer, so I'm not gonna cut on all of 'em with the B.S. 15 round limit here now.
 
Got the front sight/barrel band done today, as well as the buttstock. In retrospect, I should have made the sight taller, but oh well. Can always redo it if I find using the sights too unpleasant.

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I decided to make the front sight blade pull double duty as the locking latch. It is spring loaded

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The buttstock plate is cut from black ABS, and I bored it to accept a piece of 3/8" steel, which serves to secure it into the carbon fiber tube with a 10-32 screw, and also has a cut for the front sight latch to engage

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Now just the rear sight, trigger forward stop, and some more hand finishing to make everything look sharp!
 
That. Is. Amazing. MachIV. Well done. :cool:

I can't help but think about the rear sight with that fold over the top barrel.

You've probably already written about that issue, but I admit I'm too lazy to look back through the thread.

It looks like an option would be to mount a fold down rear sight integral to the receiver that would fold backwards to lay above the rear stock tube. It would be thin, but might work something like a fold down tang sight on a lever action rifle.

Or, a fold down rear sight that folds flush into the top of the receiver between the picatinny rail sections. Kind of like fold down back up sights I've seen on higher end hunting rifles.

I'm definitely interested in what your solution will be.
 
It looks like an option would be to mount a fold down rear sight integral to the receiver that would fold backwards to lay above the rear stock tube. It would be thin, but might work something like a fold down tang sight on a lever action rifle.
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That is exactly the plan! Spring loaded, a very simple elevation only design. Windage will set by loosening and tweaking the front sight.
 
Well, still no rear sight (probably gonna zero a RDS on it first and establish POA/POI), but I did decide that 1) the .384" barrel sticking out the end looked funny and 2) I wanna be able to use the TBAC can I ordered recently on this, too, so I made a 7075 aluminum shroud, threaded 1/2-28. I was originally going to thread the barrel 3/8-40, but didn't really feel like removing it, and it would have needed a pin or set screw to lock it down anyway, so I just opted for three 10-32 set screws from the bottom.

I think it looks better

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Rear sight done. In fact, other than cerakote, rifle done! :D

.375" wide, 7075 base, spring loaded, pivots on a 1/16 pin through the receiver. The aperture is ABS. They mate with a .250" wide, .050" deep groove, female in in the base. A single 4-40 screw secures the aperture. I tried to use a laser boresighter to glean an idea of the height, but ended up using most of the .300" slot to zero at 10 yards. We'll see how it does at 50, but I may well end up making a taller aperture piece. The good news is that my face isn't squished down as far as I thought it would be!

No accuracy report yet, but I was able to consistently nail a 4" tall piece of 2x2 at that 10 yard range. the aperture bore is 3/32", but I may take it down to 1/16", as I can see the entire front sight assembly through it.

There is no actual detent, but the plastic piece is a snug fit in the receiver groove, so it will stay down on it's own against the 0.010" wire spring.

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Incredible, just incredible. Any plans to sell your idea? Any chance of production in the future? I could see this thing outselling all the breakdown/survival rifles on the market by wide margins.


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Any plans to sell your idea?
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Yes.

Any chance of production in the future?
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That depends on if I can interest a manufacturer! I simply do not have the means. Even with fixtures and jigs, I'd still be into each one for 50+ hours on manual equipment. I'm gonna try to pitch it to Kel Tec first if I can get a hold of Sean there. If they aren't interested, I'll move on.

I would love to see it go production, and would accept a pretty small amount of compensation plus recognition for the design from a manufacturer. I think it could be done very cost effectively with an injection molded receiver, and would end up a few ounces lighter.

This critter is proof that polymer construction isn't necessary for light weight, though. Even with the chunky aluminum muzzle adapter, it tips my scale at 38.8 ounces. I just took the concept of my last build using mostly aluminum, titanium and carbon fiber a step further. That 17" long pistol with two 10-1/2" barrels came in at only 46.6 ounces. For those who didn't see that thread:

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Incredible, just incredible. Any plans to sell your idea? Any chance of production in the future? I could see this thing outselling all the breakdown/survival rifles on the market by wide margins.
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I'd buy one.

Amazing work, Mach.
 
Better video with finished rifle. And no, that's not a suppressor that doesn't work very well on it; it's just an aluminum flash can, which makes a .22 LR pretty dang tolerable without ears on an outdoor range.

 
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