Collapsing Stock For A Custom Crosman 1322 – Part 1

In a previous post I wrote about modifying a Crosman 1322 air pistol into a rifle. I did that project for someone else, but I have a Crosman 1322 too. I wanted to make my own custom rifle. Mine would be a little different, though. I wanted something very compact, that would easily fit into a small backpack and quickly deploy into a rifle capable of hunting small game.

A Better Crosman Backpacker

Crosman created their “Backpacker” pistol/rifle (now renamed the Drifter, but mechanically identical to the Backpacker) on an interesting concept. It could be used as a pistol, or you could attach a stock and use it as a rifle. It would pack down small, so you could put it in a backpack (hence the name). Such a rifle would be a great addition to a survival kit.

I am going to set aside the question of whether such a rifle would, in fact, be a great addition to a survival kit. It’s a very valid question, but even if we accept that it would be, the Crosman Backpacker suffers from a flaw: the stock is kind of awkward.

The Crosman 1399 stock screws onto the frame of the pistol in place of the normal grip panels. So to put the stock on, you have to grab your gunsmith’s screwdriver, unscrew the grip panels (there are two, one on each side) and remove them. Then you slide on the stock, and screw it on in place of the panels. Not exactly convenient.

The stock is pretty bulky, too. All in all, I wasn’t a fan of the design. So I decided to make something better.

Design goals

I wanted the new stock to have the following characteristics:

• Lightweight
• Very compact when collapsed (or folded)
• Does not require assembly in the field
• Requires no tools to deploy the stock
• Does not affect the pistol grip panels
• Can use it in pistol mode with the stock attached (this is a lower priority demand)

Naturally, I was willing to make some compromises too:

• The stock doesn’t have to be amazingly comfortable – this isn’t a target rifle, it’s a survival hunting rifle.
• It’s OK if using it as a pistol is a little awkward.
• I don’t expect it to be completely wobble-free.

I figure that if I’m in the unlikely situation of needing to hunt for my food with a pellet gun to survive, I’m going to want to give myself the best chance of hitting the critter. So I will use it in rifle mode about 99% of the time. If this were a firearm there might be some merit to having the pistol mode for self-protection. But for an airgun it doesn’t make much sense.

As part of a survival pack, it must be light and compact. I don’t want to have to assemble parts in the field because of the risk of losing something. And I’m willing to give up creature comforts in pursuit of the major goals.

Time for a 3D Model!

I use the free version of Onshape for creating 3D models, and creating mechanical drawings from the models. For me, the latter feature is important as I don’t have a computer in the shop, and the machines are manual anyway. So I need good old mechanical drawings for the metal bits.

The design is inspired by the collapsing stock of the H&K MP5 submachine gun. The rods supporting the shoulder stock slide alongside the receiver tube of the gun to collapse the stock, and pulls out and locks into place to shoot.

I designed a plastic, 3D-printed shoulder pad. A pair of aluminum rods give the stock its length. I will notch the rods in several places so the stock can be locked into position. And I designed a latch mechanism to lock onto the notches, and attach the whole assembly to the pistol. The latch replaces a plug at the back of the pistol.

This is the design I came up with.

Time to start building! Stay tuned!