^^ M ou can make a lower receiver, con-^kf sisting of a trigger housing and mag-■ azine well, from 14-gauge sheet I metal. It can be cut in one piece and bent around a form block. This requires welding a seam along the bottom. Or it can be made in two parts, which are considerably easier to form but require welding the same seam as before plus another down the front of the magazine well.
Regardless of which method is used, you have to make up a form block .900-inch thick, 1 1/2 inches wide, and 7 inches long. This will likely require cutting 1-inch-thick material thinner since material as thin as this is sometimes hard to find. It may be easier to bolt, rivet, or weld together a 3/8-inch thickness and a 1/2-inch thickness with an .025-inch shim in between; .22-gauge sheet metal is almost right for this.
Lay out a full-size pattern, or template, using the dimensions shown in the drawing. This is then scribed directly on the sheet metal and a full-sized blank cut to shape. This metal is too thick to cut with hand shears, so a fine tooth band saw should be used. It can be done with a hand hacksaw as a last resort, but it won't be fun.
If you use the one-piece blank, bend the magazine well portion around the form block by clamping the blank and form hlnck in a heavy vise and bending the exposed side to shape with a block and heavy hammer. The opposite side can't be formed completely in the vise. But it can be started and partially formed and then finished with the hammer after removal from the vise. The ends of the two-piece blanks are bent at right angles either by the same hammer-and-vise method or through the use of a sheet-metal brake. The seam should be welded, using the form block as a spacer, before proceeding further.
Now that the two pieces are welded together, this blank is, for all practical purposes, the same as the one-piece job, and they are both treated the same from here on in. Turn the blank upside down and clamp it in the vise with the form block between the two sides. You should block up the area between the vise slide and the form block to keep it from moving downward in the vise. Then, using a heavy hammer and block, fold the lower
Cut from 14 ga.sheet, two required
Cut out to permit Safety to function, if closed bolt version is used Slot is 1.875"long by .375" wide / A5Q,
Lovoer receiver template.
Receiver End Cap
End Cap .250" Thick
Lower receiver components.
sides over, forming the bottom of the lower receiver. Now weld the seam with the form block kept in placc w hilc the welding is done. Unsupported sheet metal has a bad habit of changing shape when heated.
Cut a back plate to size and weld in place across the back of the magazine housing. If a milling machine is available, this can be made with the magazine release housing integral. If not, you will need to use a sheet-metal plate welded across the back and to fold the housing from sheet metal and weld it in place. A slot must be cut through the back plate to allow the magazine release to engage the magazine. Weld a similar filler plate in place at the extreme rear end of the trigger housing.
Magazine Housing Back Plate. Weld in Place
Front Hinge Block. Weld in place.
Weld a 3/4-inch steel cube to the upper front of the assembly. The edges should be beveled and welded all the way around and built up above the surface, depositing enough extra metal to form a concave fillet around both sides and the bottom. Slot this block on the top center to accept the front mounting lug of the upper receiver.
The upper surface of the assembly should now be machined flat and square and cut on the inside to a concave cross section to match the radius of the upper receiver. This includes the block welded to the front end. The easiest way to do this is with a ball cutter in the milling machine, but it could be done with files if required. Now slot the front block to accept the front receiver lug using a 1/4-inch end mill.
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