So, in the time between the suppressor design that I am doing for work, I decided to go after a semi clandestine manufactured SMG. The criteria driving the design is that round tube is incredibly common in SMG designs, so I wanted to avoid that and use rectangular tube and bar stock. This minimizes the operations that require a lathe, and while they ideally would be done on a mill, they can be accomplished with a drill press and hand tools if you have the patience. Some of these parts are innocuous enough that they could also be farmed out to local machine shops without raising eyebrows. Strangely, one of the larger issues that has faced clandestine small arms manufacturing is an acceptable human interface. Other people solve this by traditional methods such as carved wood grips, or cast/molded plastics, but that is a time consuming process to make a part that should be very simple. My solution was to use handlebar grips from a bicycle. They are already designed to provide a griping surface for your hands, and they are common enough and varied enough that you could will not have a problem sourcing them.
As far as the design goes, it is still a work in progress. The receiver is pretty much dialed in, as are the trunnions, the barrel, barrel retention system, etc. The FCG has been a sticking points, as designing them is probably my greatest weak point when it comes to arms design. As the FCG is horribly incomplete, the bolt may similarly undergo changes. It is currently planned to have a linear hammer, but that is still in the works. I have only begun to consider what to do for the stock, and the forearm will probably come last. The design uses Uzi magazines, and I'm toying with the idea of being able to change magazine compatibility by having alternate lower receivers.
There are two primary versions; the 9" barrel original design, and the 5" barrel design.
Charging handle/bolt/action spring interface
Early receiver, designed to be cut out of 1x2" 11ga rec steel tube. The notches near the trunnion and front barrel support are to allow the components to be welded together.
charging handle and barrel retention system details. The action spring guide rod runs through the front barrel support and in conjunction with the receiver it locks the barrel retainer plate in place. The retention plate slips into a grove cut into the barrel. This prevents the barrel from moving backwards out of the receiver, while the square section at the breech of the barrel nests in the trunnion to prevent forward movement. The barrel is not rigidly fixed to the receiver, but this is acceptable considering the intended applications of the weapon.
have question about 12.7x99 AP M2 cartridge WWII time books gives muzzle velocity for AP M2 - 895 m/s for 45in barrel, modern days firing tables and manuals gives 856 m/s for 45in barrel, which is correct, or both correct but 1st for WWII and 2nd for modern dayes cartridges ?