Ultralight Folding 9mm Pack Rifle Begins

I've become very fond of the .22 Pack rifle I built, and being that I haven't had a 9mm carbine since I sold my Camp 9 back in '13, it was a perfectly logical progression to make a 9mm version

It's gonna look a lot like the .22, just slightly wider and longer in the receiver. Obvisouly, a 9mm blowback bolt needs to be a good bit heavier, too. Like 16 ounces vs. the 6 ounces of the .22 bolt. And of course the barrel is bigger, so I expect it to come in between 3.5 and 3.7 lbs (for those who don't recall the specs or never saw the thread, the .22 pack rifle is 2 lbs 6.1 ounces). The most notable visual difference will probably be the angle of the mag well, which I'm going to carry to the exterior profile. It will use Beretta 92 magazines, and the catch will be external on the front, sort of a shoe, if you will, although I haven't yet decided if operation will be pushing forward or if it will be a lever that presses back against the mag well. Anyway, this is basically the receiver design (red denotes bolt bore, blue for magazine well):



Decided to start last night, so I lobbed off an 8-1/2 chunk of some 1.5"x 3.2" 7075-T6 I had and squared it up.

Being a deeper and larger bore (1.000" x 6.700"), I wasn't able to use my preferred vertical boring and reaming configuration. I had to ponder how I wanted to attack that for a little bit, and then decided on my 90° milling head. I don't use it very often, but when I need it, I need it! I hate unbolting and removing that heavy Troyke rotary table (208 lbs), so we just used it!



I also had to make a shank extension for my 15/16 S&D twist drill to get my 6.700" depth. It was slow going with the short flutes, pecking .200" at a time, but we got it! Then is was on to reaming with the 1" carbide tipped reamer I actually had on hand



And after a long evening, we had a block with a hole!



I had a bit more time to mess with it today, so I began profiling the front of the receiver and made the ejection port and charging handle cuts. Will probably do more later tonight, but gotta go shopping and need to spend some time with the kiddo.



A long way to go, and I have lots going on right now, so I don't know how rapid the progress will be, but I'd like to have it done by Chrismas. The 1" 8620 stock for the bolt showed up yesterday, and the 9mm barrel liner and carbon fiber tubes are en route. Shouldn't need to order anything else, just got lots of cutting to do!

Stay tuned!

One question. Why the choice of beretta 92 mags as opposed to a Glock mag? Already have a beretta 92?

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Yeah. It was between that, CZ-75 pattern, or S&W 59XX. Easier to find 20 and 30 rounders for the 92, though (I do have 20 rounders for the 5906).

That Marlin used 5906 mags, which was kinda cool.

As well, using the Beretta mags, I could add a secondary catch that would allow use of CZ mags. They're almost identical except for the mag cut, and I have run Beretta mags in my Baby Eagle 9mm with a second cut. Only downer is once you do that mod, you have to hold down the mag catch to insert them in a Beretta.

Sweet, glad to see you starting in on this! 9mms can apparently be built with some crazy light bolts (I saw some guy with an open bolt MAC that he'd lightened the bolt even further on, as well as reduced travel, to obtain an insane cyclic rate of like 1700rpm or so)

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One can get away with a lighter bolt in an open bolt gun, though. Advanced igntion; the cartridge is trying to push back a bolt that's still going forward. That's why I had initially considered doing an open bolt on these pack rifles. but I just couldn't think of a good way to build them that they wouldn't be stutter guns if the JBTs took one and yanked the fire control parts.

Any concept sketches of what you want the stock to look like? I assume it'll have to be beefed up a little above your 22LR prototype version.

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It'll be the same. There's no need to make it stronger. I could jump up and down on the one on the .22 pack rifle. Carbon fiber tubes are stupid strong axially, and the ABS piece is plenty stout too.

It's getting lighter

Change of plan on magazines. We're gonna make DB9FS mags the primary. They fit the well perfectly, and the cut is high enough to have a catch in the receiver. However, I'm also going to make it capable of using Beretta mags so I can still take advantage of those 30 rounders. I'm not sure if I can feasibly make it an attachment to the DB9FS catch, or if I'll just make a second catch that extends below the receiver, but at worst, switching between magazines will only require swapping out the catch with a single screw or pin.

Using the DB9 mags also goes with the ultralight concept, as the DB9FS is 12 ounces lighter than a Beretta 92 (21.5 vs. 33.3), and I'm less concerned with holster wear and scratches on the cheaper (but very good) pistol, so it's a better companion gun, IMO.

I'm glad I made this decision before profiling the mag well!

I might even make another catch and mag well insert that allows use of the thinner S&W 59XX mags

What size endmill are you running down the pic-rail, and how deep? I'm making an MP5-thing with a beefy steel rail out over the cocking tube support, and I think a similar 'trench' down the middle would drop the weight out near the muzzle. Just not sure how much can be removed before the rail is either too weak or no longer secures mounted items.

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I use a 3/8" 4 flute Garr carbide critter with an .050" chamfer .150" deep, then come back across the top of the 3/8" wide cut with a 5/8" .100 chamfer.

Unless you're using gorilla torque, they're still plenty strong. I've done the same on AR rails. I just wouldn't recommend running all the way through the front or back; if you do, and you ever drop it, bending one side inward is a probability. If you're really concerned about squashing it, just do sections maybe 1" long and lave 1/8" between each. This is what I did on the handguard for the featherweight AR, because I was going all the way through:

Well, I had two vehicles to work on today. The first ended up needing almost nothing, and the second I now won't see parts for until Monday

On the upside, though, it gave me some time to work on this critter. It's pretty much an "80%" now; the exterior of the receiver is basically finished, and only fire control pocket and pin holes to be done inside. It's difficult to see unless you look closely, but there is a lot of detail work as far as rounding & chamfering, applying radii, etc. This stuff is easy for a CNC, but it's a whole lot of operations on a manual machine. For instance, when you want a chamfer higher up to match one below it, you either have to adjust the depth and radius on the rotary table, or if you're lucky, you'll have a cutter with a proper chamfer radius in your selection to do inside radii. And then to match it on the off side, you start all over again, being certain that you measure off all the same points for X,Y,Z after having re-zeroed the radius on the rotary table.

Anyway, it's pretty close now. It's 16.4 ounces as it sits, so should be just under a pound after hogging the FC pocket:

I hope you are taking the appropriate steps to protect your intellectual property

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Not much I can do other than not share with you guys. Even if I could afford to patent, I couldn't afford to defend that patent in court. Honestly, I'd be pretty flattered to see my designs go production, and figure I could probably get a little something out of whoever rips me off with the threat of small claims, where the bar is much lower due to the amounts involved.

Heck, I'd OK Kel-Tec taking my designs if they'd send me an RFB and a CMR-30 as consideration for the IP!

Barrel showed up yesterday afternoon, so I wasted no time in getting after the next step. It was 21" long and flush chambered, so we cut it to 16.6", faced off the rear so the rim is exposed, then turned and threaded the muzzle end. My original plan was to thread the chamber end as well, but alas, though I have a 9/16-24 tap, I never purchased the accompanying die, and NF is too deep and too aggressive, so we had to come up with another mounting solution. That solution was to make the barrel block insert a press fit, and then use four TIG spot welds to be extra sure it's not going anywhere. Last night and part of today was making the barrel block, and then this evening I got after the insert, which is cut from 1" 8620 steel, then heat treated. The feed ramp is integral with the insert like my .22. Unlike the .22, however, this is not just a straight piece. It is stepped inside and out. Outside is .800" for .700", and the rear .200" is .998". Inside bore is .564" .830" deep, then .480" for the last .070". Reason for that inside step is to keep from driving the barrel too far. The outside step is because there just isn't enough aluminum for a press fit with a full 1" diameter, the base of the ear bevels being only 1.046". The bore in the barrel block is actually .800" deep, but I had to leave room for the spot welds.

Final cuts on the barrel block insert:





And with the barrel beaten into place and welded:



Next was pressing it into the 7075 barrel block. Not much of a task for a 20 ton press:





And the there was fitting the assembly to the receiver. My .200" protrusion of the extension into the receiver, plus the feed ramp, made for some interesting relief cuts. Did what I could with the mill, but a lot of it was hand profiling with a Dremel:



And this is where I call it a night: