Ergonomical Opinionings Requesterated

[Nom de Forum]

Not that barnbwt is much concerned about marketing, but I think there is definitely a market for the unusual, especially if it is very functional. "SKS, Ruger mini-14, M1 Carbine, Ruger 10/22, Keltecs, Savages, .410 shotguns or any number of $500 rifles" - Boring . Some people like to step away from the mundane to have fun. barnbwt I am ready to be put on the wait list as soon you have a well functioning design and are ready to build more.

 

[barnbwt]

I scribed out the cut lines on my receiver tube today (which I suppose makes it a "firearm" in the eyes of the ATF per the EP Armory ruling ) to get a real-world feel for the size of the thing. CAD is extremely misleading with regards to perceived size, since every detail you look at is approximately palm sized when you work on it zoomed in, so soon all the large and small parts grow & shrink in your mind's eye to be closer to the same size. This gun will make an M1 Carbine look/feel like a fat kid. It really is more of a 'machine pistol' than a carbine, the main body being a smidge longer than a Mini Uzi, and smaller in all other dimensions than many service pistols (without a mag or stock, obviously). But for the long barrel and stock, it would have the same profile as a sawn-off single shot 12ga.

The foregrip is short, but only because the full-size stock I currently have to mock up with (14" LOP) is disproportionately long and rakes the weak hand grip angle back to about 45degrees. A short 12 or even 10 inch LOP would bring the rifle in closer and get the wrist closer to 90 degrees out from the barrel. The short LOP will also get the carbine square in front of the shooter like how many do their M4s and other low-recoiling rifles (this has the benefit of seemingly making the shooting hand grip more asymmetric and less variable; you pretty much have to put your thumb on the strong side to be comfortable on a straight stock, and if I put the sights real low, you won't be able to use them if you wrap the thumb over the top)

I found there will be an immense temptation to wrap the thumb or fingers over the receiver, right were the gas vent will be evil along with a reciprocating bolt carrier through the lightening/vent cuts at the fore, so I need to come up with a clever means of discouraging that through non-painful ergonomic means. Perhaps an angled grip to move the hand back toward the magwell (or just a taller forestock to drop the hand down), or a very short vertical foregrip that would be gripped by the thumb and one or two other fingers (the gun is so small and light that this might be more practical than I'd think at first glance). Maybe even a 'sabre handle' flat loop below the barrel that the fingers curl into and the thumb wraps around the front of.

As far as cost, I'm one 30$ 308cal demill Winchester 100 takeoff barrel (Numrich), 150$ in 4130 tubing (and we wonder why no one builds stuff in America anymore ), a 10$ share of 4130 bar for the bolt/flaps, 50$ for the PPSH mag and magwell adapter, and probably another 50$ in 4130 for the FCG parts, lower receiver structure, and pins/springs. The stock, if you really want to count it, is probably 30$, but it came from my parts pile so it's free to me. Minus labor, cuz I'm having the time of my life designing/building this, it probably comes to 400$ or so if I don't waste money on dead-ends along the way (yeah right).

In a manufacturing setting, the receiver could be completed in two jigged positions in minutes on a light CNC machine, and the two telescoping receiver tubes would then be oven brazed or welded to each other. The bolt would take longer being billet, but is probably a 3 position part (flaps are 2 position parts). I also suspect materials costs would be less than half with bulk/contract agreements that eliminate shipping additions. In short, I think the gun could probably be made for 300$ or so, which is about as cheap as you can build anything that isn't Zamak or cranked out by the billions on mass-production equipment.

TCB

 

[leadcounsel]

Best of luck to any entrepreneur.

However, moving the selector switch and the angle of a rifle, and a few other changes for the sake of changes wouldn't make me a consumer...

As I mentioned, there are a plethora of tried-and-true designs and I've rarely thought about ditching one of those because of the angle of the grip, or location/design of the safety. *Could* they be marginally better... sure, I suppose.

But that misses the point. The lions share of the rifle market are AR15s, AK47s, Ruger 10/22s, Bolt rifles, SKS, and Mini-14s/30s, pumpguns, lever actions, etc.

A novice is being dis-serviced by shielding them from the operations of the majority of the rifles by learning on some unique proprietary design that shares nothing in common with the above referenced long guns.

It would frankly be better to teach a novice on a gun they might actually encounter or purchase in the real world, rather than some unique gadget they may never see again.

Say you get to spend 5 hours with a novice to teach them how to use a long gun. You'd be better off grabbing a handful of the most common and diversified long guns to teach them how to operate - say an AR15, a pump gun, a lever action, a bolt action and an AK47. Spent a solid hour with them on each platform, and they would be competent with the overwhelming majority of rifles found in America. But if it can be only 'one' rifle, again, I'd say take one from the above list, not some unicorn ...

Just my 2 cents.

 

[barnbwt]

"I have a number of features devised to make things easier and more intuitive for them, which I'll list below in case you'd like to suggest/add things. (Please refrain from turning it into an AR )"

I would consider AR/AK features, but they'd have to earn their spot; there's no sane reason a designer with free reign would choose an AK safety, or AR charging handle, for example.

TCB

 

[kayak-man]

I've got a few thoughts, no idea how mechanically feasible they are, just throwing this out there:

-For ambi brass ejection, would it work to have the brass ejected straight up, and have a curved piece of metal that you can rotate to deflect it either left or right?

- charging handle on the forend is interesting, but I feel like it may not give the best leverage for a new/ unfamiliar shooter, and to me, it just seems awkward. maybe something like an FAL style folding charging handle on the side would be a little more ergonomic, and out of the way? If you could find a way to mimic the tip-up barrel of those little Berretta autoloaders, that would be sweet!

- I'm assuming you want to keep it in a rifle or subgun caliber, but what about 9mm?

Honestly, I don't really know what I'm talking about, and if you decide that my input was complete rubbish, that's fine by me. Either way, I'm super excited to see what you end up with.

 

[barnbwt]

Thanks for the input, Kayak. Feasible or no, they are ideas from outside my head and therefore appreciated

-The shell deflector is my fall back (as is simple vertical-forward ejection), but it seems like it'd be rough on brass, which is a really bad thing for reloadable tok brass (as well as for cut down 223 brass)

-I, too, think a forward handle would be nice (though I personally don't think a FAL or G3 handle is all that small even folded; just not obnoxious), but I really just don't see a place to put it. Unlike those guns, there is no parallel tube for the cocking tube or gas piston on my rifle; the piston is concentric to the barrel. That means my cocking options are limited to hooking onto the carrier right around the barrel. The sights block the top plane, and I'd like to keep the sides as clean and snag free as possible (if at all possible). Hence my thinking of putting it on the bottom plane. Side or top cocking would work if I could do it in an extremely low profile manner that was also still somehow easy to access. I at least have more room to work with on the bottom from the foregrip wrapping around everything. I'm even looking into whether a levered foregrip (think pellet rifle) would make enough bolt carrier travel to work. The pump action idea seems the most practical for the time being (would be a bit weird to pump past the barrel on an SBR, though)

-9mm is a distinct possibility since it feeds from PPSH stick mags, but the locking system of the rifle is probably wasted on it; the mass of bolt/carrier alone are probably enough for a safe blowback (though it'd still be close on that count). With the right gas port, 9mm would likely have enough gas to cycle it, though. Hot 9mm Largo or another 'magnum' 9mm round would be a hoot, though.

-My barrel is actually a quick release type, with two large lugs that rotate to engage matching lugs in the receiver tube like a bolt action. The locking action actually tensions the barrel (and would improve accuracy on an SBR without an ant-eater nose) against the nose of the receiver. Kinda precludes a tip up design, unfortunately. A 'break action autoloader' is kind of a neat concept, though, and would seem to work for all fixed-barrel designs, so long as the receiver is laid out to accommodate it. My receiver, being a tube, just doesn't have the meat on the underside to keep everything together like a pistol frame does.

Here's a newer mockup picture, using the marked-up steel tube to show the relative size of the thing (barrel is positioned behind, not inside, the tube because it has not been turned down to the .58" OD I'll end up with). You can probably see the cut line 2" from the end of the tube, which would like up with the stock. You can also see the cut traces at the front of the butt stock. Most importantly, see the 1" square tubing that makes up the core of the receiver; not a whole lot of room for stuff in there. As I said earlier, the current LOP is out of whack with the size of the gun; 13" is closer to long rifle size, so I'm thinking 10" is probably more fitting. The gun is basically sized like a toy gun, but can pack some pretty serious power when you start talking 10mm from a Shpagin drum or hot-rodded 7.62x25. The drum would cut a good 3" off the overall height (and add it to each side)

TCB

 

[barnbwt]

How's this for a possible solution to my grip safety/ejector selection switch;
-A flush-set button on the sides of the grip where one of the shooter's finger tip would depress it, but where their palm on the opposite side would not? I'm thinking the middle finger would be the best since it's the most dexterous after the index finger (and for good reason )

I've whittled down the Steyr stock quite a bit so it's not near as fat and straight as it was (deeper comb cut, smaller inside radius on the grip underside, and thinned the sides). Now, the middle finger just happens to lie pretty much on top of the holes for the sling-swivel Steyr stupidly installed on the side of the grip, originally. That's what gave me the idea.

Again, I would try for a button that only takes a pound or two to actuate; does that still sound like an awkward solution?

Hopefully I'll be able to cut metal on my receiver tube tomorrow, and the mockups can start looking better

TCB

 

[Sol]

The charging handle is reminiscent of a FAMAS or Clarion or whatever it is.
Except it's on the bottom not the top.

 

[barnbwt]

Early AR10's, too

TCB

 

[barnbwt]

Alrighty, I'm gonna try to do a slide-action foregrip in lieu of a protruding charging handle for the following reasons;

-Cleaner appearance/smaller profile
-Full protection of hands from hot gas (no slot for gas to blow through)
-Stronger mechanism (it's easy to add strong metallic rails for a slide to ride on; a narrow handle, not so much)
-Hidden small parts (dirt/debris)
-Short action throw (2.65" is short enough the motion would not be awkward)

Possible cons:
-Less movement for shooter forearm (there are benefits to both methodical and intuitive motions for charging, namely what the other hand might be unintentionally doing around the ejection port vs. how fast it takes to perform the operation)
-Moving the support hand toward the muzzle (and beyond it in an SBR format) seems less than desirable. If a careless shooter thrust his hand forward without enough grip to drag the grip with him, his hand would be forward of a live muzzle (unless I also incorporate a grip safety that would require a two-handed grip to utilize). This is mitigated by the action having a short 2.65" throw and lightweight springs

In any case, I think the cons are minor enough that I'm giving the slide action a shot. That raises some questions about function that I hope ya'll can help answer. The slide will be held to the rear when firing, but is thrust forward to latch onto the bolt carrier then pulled to the rear to cock the action where the slide automatically disengages.

-I want a positive catch holding the slide to the rear except when cocking. Would you prefer a finger-activated switch (probably on the front end) or something like pulling down on the foregrip itself to unlatch it for cocking?
-Would you like the slide motion to automatically lock the bolt back until the switch is released? I do plan on having a dedicated last-round-bolt-hold-open with manual de/activation so this might be redundant
-Even though there is no spring resisting the forward motion of the foregrip slide, does a smallish Schnauble-style fore-end swell seem sufficient to keep a weak hand from sliding forward into the line of fire? Is it even needed?
-Do you think a grip safety is needed, or at least a 'full back' safety, to prevent the gun from firing with the slide slightly forward (the returning bolt would snag the slide and snatch it from the shooter, and their fingers would be forward on an SBR muzzle)?

TCB

 

[sawdeanz]

Just wanted to let you know I'm still following. Can't wait to see videos if the action. I think the pump action is intuitive, why can't it just catch the bolt on the rear stroke instead of pushing it forward first?

 

[barnbwt]

Sliding forward first allows the action to be 2.65" shorter during firing . Lots of Czech heavy weapons cock this way, but using the pistol grip rather than a forearm.

TCB

 

[barnbwt]

Per some recommendations on another forum, the safety/selector lever layout will work thusly;
-Just by happenstance, the sling-swivel hole is right where my middle-finger tip rests
-I will run a flat, slightly-below flush lever from this hole around the front strap and around to the other hole on the far side of the stock
-This lever will effectively function as a finger groove, and will be pulled ~1/16" toward the shooter's strong side by their grip (assuming they grip between finger/palm like a normal person, and not finger/knuckle, which might prevent the lever from moving properly)
-The lever will position a piece inside the receiver that will cause one of the ejector pins to not be projected from the bolt face against the case head (not pressing the lever will fire both out, sending the case vertical as opposed to a FTE)
-The lever will also move a tab restraining the tail of the trigger (the recess block in the trigger animation) and enable the 1-2 stage trigger (finger pull technique determines specific trigger let-off feel)

TCB

 

[barnbwt]

The journey of a thousand miles, begins with a single step...or CNC stepping servo, to be specific

Got the upper-side cuts and locking recesses cut into the inner receiver tube (the main body of the gun). Eventually a "saddle" of larger tubing will slide over the recess area and be welded/brazed to bridge the receiver. I'll have to put together an updated mockup of the parts I've got so far

So far, it looks like the CAD . Next step is getting the bolt design finished up, so those parts can be made/fitted to the tube as it is. At this point I'm thinking I'll do the twin-ejector pin concept since the duplicate parts are at least easier to make in that configuration.

Since I have also gotten the stock to roughly the shape I want for this, I will mark out several locations for the grip safety levers along with my hand position for your perusal.

TCB

 

[barnbwt]

Here's the latest 'mockup of a mockup' using the stocks, receiver tube, and M1 Carbine sights.

I plan on cutting the stock another inch or so closer to the stamped markings, not because the LOP is long so much as the gun seems really out of proportion the way it is. I'll hold off until the barrel's on though, since that will probably even things out. Making the buttplate aluminum rather than the factory steel skull-stomper will likely help as well.

Phase Next will consist of getting the bolt assembly done, and I also need to look into the dynamics of the piston design to ensure I'll have enough gas to cook with (there's direct impingement AR uppers in 7.62x25 out there, so I'm confident it's possible, just rather close to the edge of what's possible )

TCB

 

[barnbwt]

Progress!

Ooh, man, it's been a while since I checked in on this, but I've been making lots of progress. Very slow going, though, making steel parts without a mill. I'm holding .01-.03 tolerances, and tighter where it counts, so the product so far is surprisingly decent (Khyber Pass standards, but from 'Murican 4130 alloy steel)

This part of the build is very important since it is the major proof of concept; can the locking wedge and loosely-constrained flaps consistently engage the locking recesses for rigid in battery lockup. It sure seems like they can

Apologies on the blurry/shakey gif; cell phone camera limits my production value, you know


What can't be seen/isn't made yet is the piston/op-rod which sits over the top of the bolt assembly as a flat sheet, and drives the wedge forward/back as well as cams the flaps inward on the driving stroke. I need to update that design to match the actual dimensions of my hand-made parts before that component can be completed. There's also some remaining details to finish on the bolt assembly (breechface, firing pin & ejector holes, firing pin block, extractor) that are about 95% firmly designed.

Back to the ergonomics end of the build, to which this thread was originally intended...
-The cocking of the action will be accomplished by a slide action foregrip. When fully back, the grip will then pivot on a sliding pin at its front downward a fraction of an inch, a detent keeping it from sliding forward unless it is first pushed/rotated up at the rear against a spring and then pushed forward. Once fully forward, a catch will snag the piston/op-rod so the whole mess can be pulled back, where the foregrip will once more drop down into the detent, releasing the bolt carrier and chambering a round. Simple, elegant, compact, and the shooter's hand is fully sealed from escaping gas by sheetmetal inside the foregrip
-For now, I think I will roll with a manually (by internal servicing) swappable ejection setup, but only for testing/debugging purposes --gotta make sure the gun cycles, first . I'm still liking the idea of a cross-pin or paddle operated by the palm or thumb determining which way the brass flies.

Attached are some progress photos of the bolt and flap(s). There's two flaps now, though. Simulating a breechface with a rod clamped into the front of the receiver for the bolt assy to strike, the lugs readily and perfectly engage the recesses (which will be further reinforced with a welded-on jacket that wraps over and encloses them). Everything is currently oversized, the 'headspace' theoretically a whopping .05" or so from where it will actually be, but you have to creep up on tolerances gently when filing parts from bar stock.

TCB

 

[barnbwt]

Now that I have a machine tool (lathe, qty 1) I was able to get the barrel knocked out fast enough . Gas piston to follow. My 1/6 turn quick change barrel scheme appears to work well enough, with the potential to be really slick if things work out well, operationally (as in mechanically; not the GI Joe guys). Also have enough of the foregrip/slide support stuff made up to do a decent mockup of the cocking motion to charge the gun)

Got the rest of the bolt assembly 'done' a while back, too (and improved, even)


1) Make piston
2) Make rear support for slide tube (which doubles as a barrel latch)
3) Finalize/make cocking pawl for slide and cut hole for it in receiver

And at that point I should at least be able to demonstrate racking of the action (gotta finish-trim the breach of the barrel and add a FCG before the action can be 'cocked' and go into battery; we'll get there)

TCB

Meh, bite me, Old Thread Warning...I'm working as fast as I care to...

 

[Nom de Forum]

Glad to see you are making progress! Don't worry about old thread warnings. Anybody with an ounce of sense knows this project is going to take a while. Nothing as interesting as this is going to be knocked out over a couple of weekends. Thank you for sharing and I look forward to reading your future posts.

 

[barnbwt]

I'm also figuring out how the bolt face/ejector are going to function (still). I had planned on a 180deg opposed blade ejector and claw, but the claw portion is difficult to realize with as short a bolt head as I have (unless I go to a Remington style circlip extractor, which I don't care for).

I'm actually thinking about a shell holder face at this time, since that takes up no more room than the bolt face counterbore (might be easier for me to make with my tooling options, as well). The main downside with a shell-holder setup, is that the ejector must sweep across the bolt face; typically a complexity-inducing feature.

Here's what I'm thinking;
-Bolt face slotted and undercutted for the case rim, but just above the centerline of the firing pin hole, the slot opens up (so the shell doesn't need to be kicked upward very far to be freed.
-A long, L-shaped lever will extend from the rear of the magwell (just in front of the retracted bolt) to the rear of the receiver. It will be able to pivot vertically a small amount at its rear end, and the short leg will extend upward at the front (to punt the spent casing was the lever pivots upward)
-At rear-most travel, the bolt will contact a surface on the lever's tail, driving its front upward into the case
-The lever has a return spring driving it back down (so it won't hook the bolt in its upward position)
-The lever can pivot further down than required to clear the bolt, and doing so will cause its tail to snag the bolt; however, the front end will rotate down into the magazine lips where the next round will be. Thus, it will act as a rate reducer/bolt hold open, only allowing the bolt to drop if a round is present in the feed lips (the bolt only reciprocates 1/8" past the magwell, so the rate reducer component is probably important for reliability)
-There will probably be a manual release for the bolt catch on the underside of the rear mag latch (the actual mag release is on the side where a thumb or trigger finger can get at it)
-If possible, it'd be really cool to see if sliding or pivoting the lever side to side slightly will direct the ejection path, as that would be an easy way to get that automatic ejection direction feature I've wanted

Ideally this gizmo would end up working much like the HK pivoting ejector blade, only kicking the cartridge up instead of forward, and would have to 'reset' before the bolt could return forward.

TCB

PS; You're not French, are you, Nom? (see sig)

 

[Nom de Forum]

PS; You're not French, are you, Nom? (see sig)

Nope. While I have an appreciation for the many beneficial things the French have done for the World, I often find them annoying. Since I may someday want to get my TS SCI clearance back you can count on me to keep the details of your work on the QT.

 

[barnbwt]

Piston head, and how it locks into the operating tube (a scrap metal mockup of it is shown here for test fitting). Very solid lockup, and doesn't seem to cause any tilt/binding on the barrel (pulling the tube smoothly compressed the spring). I wouldn't count on something like this to hold back bolt thrust, but it seems more than ample for carrying the load needed to strip rounds from the magazine. As fiddly a little part as this is and as many surfaces had to be fitted, this actually was pretty easy to make (two hours or so). As hot-roll steel was the only bar stock I had handy, here's to hoping that's good enough for a gas piston head, at least for a while.

TCB

 

[barnbwt]

The assembly locks up tight like a fist, even without a single fastener involved

Pretty much every non-cylindrical feature is cut by hand with saws & files, btw . A buddy convinced me that the rosette welds were easier to do than my initial desire for brazing, and more fool proof than pressed-in cross pins, so some small measure of modern technology managed to find its way in here, after all.

Once the barrel is reamed/headspaced, it will be ready for test fire (extreme limp mode: no gas system, no trigger group, fired remotely from a vise by smacking the firing pin tail through the rear end of the tube). Provided nothing interesting happens, the pressure-bearing parts will be heat treated and declared 'done' while I turn my attention to the trigger group and furniture

TCB