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

[Derry 1946]

Wow! Phenomenal work. Thanks for the blow-by-blow.

 

[barnbwt]

Needs engraving: "This machine kills squirrels"

 

[MachIVshooter]

Made a lot of progress on the receiver today. Would've been further along before now, but I made a calculation error and had to re-make the barrel block (Applied the radius of a 3/8" cutter instead of 5/16", an 0.032" mistake). That's OK, though. I like the way the second one came out better. Anyway, the receiver is nearly done now, just have to cut for the magazine catch and then hand finish to remove tool marks.

Machining the stem on the rear was fun. Used nigh every piece of my clamp block set trying to stabilize the 7.5" tall piece that had very little contact area on the bottom:



The fire control "pocket" I machined entirely through the slot you see in the trigger guard with extra, extra long 1/4" and 3/8" carbide end mills. Had to reposition multiple times. If I were producing multiple copies, I'd have done the math to use the dividing head for this. But for a one-off, quicker to just reposition the piece.



And other views of the 11.7 ounce receiver:







Unfortunately, I'm not quite gonna make my target weight. This is everything but the front sight and butt plate, though the CF tube for the stock is still 500mm, so what I cut off will mitigate the front sight. I project final weight at 37-38 ounces

 

[CraigC]

Too cool!

 

[jbj]

That is coming along splendidly!


Sent from 80ms in the future
Jimmy

 

[bannockburn]

I really like the very clean looking design! Minimalist gun manufacturing at it's best!

 

[chicharrones]

Wow. Just wow.

If this design performs well, I can see a gun company wanting to build it.

 

[MachIVshooter]

Thanks for the kind words, guys

I do like the way it's turning out, though I've been racking my brain and just don't think there's any way to get it under 2 lbs with an aluminum receiver. Molded polymer would do the trick, but I lack that capability. Oh well. Also been debating on LRBHO, and I think I'm going to go ahead and incorporate it. It'll have to be a sliding job from the outside on the left of the mag well, though, as there's just no good way to machine it internally with a one piece receiver design like this.

I will be re-making the barrel block one more time. My initial plan had been to pin a feed ramp into the front of the receiver, but there's simply not enough material above the cut for the latch to do that, and no way for me to make a dovetailed or T-slot cut for it without slotting the top.

Also, if anyone was wondering about the 1" portion of the picatinny section that has no cross slots at the rear, the reason for that is to incorporate a folding rear sight. Still working out the details in my head, but that's where it'll live.

A ways to go yet, but I feel like real progress has been made with the receiver 90% complete

 

[Carl N. Brown]

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.

The original .44 Rimfire Henry rifle of Civil War fame had a firing pin with two points for reliable ignition with rimfire cartridges.

The two pin rimfire firing system is long overdue for a revival.

Folding .22s are a choice for emergency use as survival rifles; anything to increase their reliability is a plus.

Supposedly better methods of making rimfire cartridges made two point firing pins unnecessary, but they didn't have cheap bulk pack plinking ammo in those days. When I had long afternoons at the range alone, nothing better to do, I would glean the range and bag discarded .22 dud rounds with one strike, take them home, clean and inspect and box, and next trip take them with an old .22 rifle and retry the rounds. The vast majority fired second strike, rotated 180 degrees opposite the dud strike.

 

[barnbwt]

I've been racking my brain and just don't think there's any way to get it under 2 lbs with an aluminum receiver

Yeah, it looks like you could theoretically sculpt some corners and things, maybe shaving an ounce or so for a whole lot of work (and losing stuff like functional sight rail/etc) that probably isn't worth it. A cut-down AR pistol grip would probably help, but again function vs. weight. Backpackers' dilemma

It might be worth exploring having an online SLA prototyping firm make you an '80%' from Nylon that you could finish out for a comparison (or from Delrin if you have a block). Sub-2lbs for an autoloader is still asking a lot, and it's impressive you got it this low; the bolt mass alone puts a rather larger lower limit on what is possible, to say nothing of the spring & receiver that must control its motion while securing the barrel. The 16" barrel length requirement in this country raises that limit even further.

Well, you've inspired me to get back on my sub-1lb lever 22LR repeater Bicycle rifle; got the milling attachment for the lathe finished yesterday, so hopefully I can start making some more rapid progress once my endmills & collets arrive.

TCB

 

[CraigC]

Far as I know, the Freedom Arms 252 has double firing pins.

 

[MachIVshooter]

Got the third and final iteration of the barrel block done today. Changed up the bottom profile a little, but the big difference is that instead of a .600" 0-1 peice pressed in, it is now a .742" diameter piece of 416 stainless that protrudes .060" into the bolt bore, and has an integral feed ramp. I also left a step on the edge of the lever pivot cut to prevent the lever from over-traveling when it is not locked into the receiver.

Still have to make permanent pins. That's a broken 3/16 carbide end mill through the upper pivot and a 1/8" coil spring through the lever just to keep it attached (a 1/8 pin is a no-go until final assembly with a .1245" reamed hole through the lever). I also still have to relieve the bolt for the feed ramp.

 

[P.B.Walsh]

I love watching your threads, amazing work!

 

[badkarmamib]

Looks like it is coming together nicely. I am really enjoying the updates!

 

[MachIVshooter]

Well, today we got the magazine catch cut machined and installed the catch, then made some springs and pins to get the lockwork functioning. Relieved the bolt for the feed ramp and magazine lips, at which point I had to try it out!

Unfortunately, not a semi-auto yet. Feeds ok manually, but tends to smash cartridges every which way when feeding automatically. That is probably on account of the minor modification I did to the feed lips to clearance for the bolt, which seems to allow the rounds to rotate up rather than just going forward. So my options at this point are either make my own magazines that control the cartridge longer, or make substantial mods to the gun, including setting the barrel back, reconfiguring the bolt, and machining to allow magazines to come up 1/4" higher.

The good news is that it fires & extracts just fine. Puzzling, though, is that ejection was 100% at first, but somewhere around 20 rounds in, it started catching empties and smashing them. Now it's doing it more often than not. Not sure what changed, as cartridges still eject very positively with manual bolt operation.

 

[jmorris]

Not sure what changed, as cartridges still eject very positively with manual bolt operation.

Did you make extra springs when you made the ones you used that you can compair them to and see if they have changed?

That's the only variable I would think you could have unless some of the metal work is changing.

You may need a heavier spring on the slide, being striker fired it doesn't have to to the extra work a lot of .22's have to over come before the bolt begins to gain momentum, cock the hammer back.

 

[MachIVshooter]

Did you make extra springs when you made the ones you used that you can compair them to and see if they have changed?

No extras, but I know how long the striker spring is. Bolt spring was a commercial one for which I do have a spare.

That's the only variable I would think you could have unless some of the metal work is changing.

It did occur to me that everything beginning to move more freely with wear may have sped up the bolt.

You may need a heavier spring on the slide, being striker fired it doesn't have to to the extra work a lot of .22's have to over come before the bolt begins to gain momentum, cock the hammer back.

No hammer, but the striker spring adds noticeable cocking effort.

I'm more concerned with the feeding, though. Ejection issues are easier to deal with. I tried making new feed lips and grafting them onto the mag, but all I accomplished was making a predictable type of jam where the round is smashed with the bullet on the feed ramp and the rim under the bolt. Feeds fine when you draw the bolt back and let it go, but the much more violent action of self loading changes everything.

I may try to polish the bolt face and get a more powerful spring in the magazine before I start making more serious alterations, but I'm not too optimistic about that working.

 

[jmorris]

I'm more concerned with the feeding, though. Ejection issues are easier to deal with. I tried making new feed lips and grafting them onto the mag, but all I accomplished was making a predictable type of jam where the round is smashed with the bullet on the feed ramp and the rim under the bolt.

Does it make any difference if the mag is fully loaded vs just one round to be picked up?

Somewhere in the thread I think you mentioned using a Remington 597 magizine. They have made 3 generations of them to get them to run in their rifles and I am not sure what version you have but the pot metal housing one works in my 597. It would not be very easy to modify (at least not that would last long) but maybe you could try the other designs?

From your skills I bet you could build your own housing faster than fedex could ship a different mag to you anyway.

 

[MachIVshooter]

It would not be very easy to modify

Oh, not that difficult, either





Machined new feed lips from 7075-T651. .195" thick, took my 1/8 x 3/8 keyslot cutter and made the blade 0.060" tall. Milled off the very top of the stock mag and cut 0.020" deep grooves down the side with that cutter. The new feed lips slide into the grooves on the mag from the rear, and it's epoxied in place. The new relief for the rims to come out is .300" further forward, and I was able to squeeze the billet lips just enough to keep the cartridge body down yet still allow the bolt to pass through.

We'll see. I'm still thinking trying to make this thing feed like an AR with a good step and a decent amount of distance to the chamber may have been a bad idea. Most rimfires hold the round nearly inline with and just a fraction of an inch away from the chamber.

 

[MachIVshooter]

Well, after much fussing with the thing over the weekend, I've decided to move the magazine up and redesign the bolt. I think I can make it function without setting the barrel back so long as the cartridge is more inline with the bore.

I've also decided to make the bolt out of 360 brass, definitely as proof of concept and possibly as a permanent solution. The SS bolt is heavy enough to keep the cartridge in the chamber until pressure drops, but moves too quickly and lacks momentum to overcome the recoil and striker springs. The result is that with a lighter spring, I can make lower powered target ammo and CCI "Quiet" .22 eject reliably, but with normal HV or hyper velocity ammo and using a heavy enough spring that the bolt isn't slamming into the receiver, the bolt stops it's rearward travel a tad early and returns too quickly, catching empties before they can get out. A brass bolt will be 10% heavier for the same dimensions, and is nearly as hard as the annealed 416 SS (82 vs. 78 Rockwell B)

 

[jmorris]

How much stroke does the bolt have?

Might try a progressive spring setup to help slow the bolt "slamming into the receiver" issue or maybe just a buffer.

If you want a quick check to see if a 10% mass increase is your solution, I bet you could machine another cocking handle that weighs more, so the total weight bolt/charging handle would be the same as a brass one.

 

[MachIVshooter]

Might try a progressive spring setup to help slow the bolt "slamming into the receiver" issue or maybe just a buffer.

That's less of an issue than the return speed catching empties, which only gets worse as spring rate increases. A progressive would launch it forward even harder.

If you want a quick check to see if a 10% mass increase is your solution, I bet you could machine another cocking handle that weighs more, so the total weight bolt/charging handle would be the same as a brass one.

Could, but the bolt needs to be redone to resolve feeding issues anyway. None of the tweaks I've done to the feed ramp, throat, mag or bolt face have made it able to feed reliably with full bolt speed. As well, I want to be able to use unmodified 597 mags, which means narrowing the slot in the bottom of the bolt slightly to in turn narrow the outsides so they may pass through the 0.192" apart lips. It's not much difference, but enough that the rails which catch the cartridge would have been razor thin with the 0.160" slot it has now. Not only high bend/break probability, but 0.010" is thin enough that a jam could cause enough denting to ignite primers with the bolt wide open. If I narrow the feed ramp to .120 and the slot to .130", I can have 0.025" wide rails hanging down, allowing 0.005 of wiggle and rotation to either side, as well as variations in mags, without hitting feed lips.

 

[spazzymcgee]

Very, very cool. Have you thought about what you're going to coat it with? Or were you going to leave it bare?

 

[MachIVshooter]

Probably sniper grey Cerakote. A buddy of mine is one of their "certified" applicators, and it's nearly free for me if I can wait until he's doing other guns/parts in the same color. I'd like to anodize, but not set up for that yet.

 

[jmorris]

What is the stroke length of the bolt?