Sheet metal, as used in this project, can usually be obtained locally. I he 12-gatigc material can, as a rule, lie Inund in sheet metal shops and metal fabrication plants If possible, try to get the type with h role! finish, commonly known as ucold rolled/' This will have a bright finish as opposed to the rough black finish of the "hot rolled" type. It will cost a little more, but the time saved in finishing it will make up for it. Salvage yards are also a good source for this. If you aren't able to obtain it elsewhere, material cut from ulder automobile or light truck frames can he used. The biggest problem with this source is the amount of work it Lakes to geL it. Actually, though, this could be an advantage* since the car frame contains heller material than c ommon sheet metal.
Leaf springs from cars or light trucks can be used lor fUl stock material, and axles from the same source will provide round stock Valve stems salvaged from four-cycle engines, as well as shuck absorber shafts, cuii be used fur small-diameter parts. Most of this material will require annealing to soften it to a point where it can be machined easily. This can be done using a large wood fire as desrrihe.d in several of my other books. If a bluing setup is available, material can
/V fieovy v/$e con be us^d ns n press brnbe to Jem $hee! A .Tîtfiai-c uUing bund suv will save a hi of eHxw yreuse.
FOUR .250" DIAMETER HOLES DRILLED EQUADISTANILY AROUND CIRCUMFERENCE OF RECF'VFR. BARREL BUSHING IS WELDED IN PLACE THROUGH THESE.
BARRF.L BUSHING 1.100" LONG. TURNED TO CLOSt I- I INSIDE RFCEIVFR.
front end of the receiver. <>ne-and-a-quartcr-inch material is slightly small for this since the inside of the receiver measures 1.260 inches. So slightly larger material should he turned to fit. While the hole through the hushing will have a finished diameter of .875 inch, it should he kept smaller and bored to si/e after the hushing is welded in placc. I he bushing should he positioned inside the receiver with .600 inch extending back into the receiver and secured permanently in place by welding through the foui holes and huilding the welds up above the surface far enough that they can he dressed back flush. TIG welding is ideal for this. II this is done properly, no trace of the welds will show.
A cube of steel 1/2 x 1/2 ' x l/2M is likewise welded in place on what will be the exact bottom ccnter of the receiver blank. It should be relieved on all four sides where it joins the receiver and builr hack up above the surface with weld material and machined hack flush. The forward edge should be Hush with the receiver face.
I he assembly is now chucked in the lathe and the barrel bushing bored to -KTS inch. There should he .500 inch of the bushing extending past the front face of the receiver. This is turned lo a diameter of 1.125 inches and threaded 24 threads per inch.
Fur both receivers to mate properly and the inside diameters of both the upper receiver and the lower receiver spring tube to be concentric and parallel, .100 inch of material must he removed from the exact bottom !>ide of the upper receiver. The ccntcrline of the front hinge block is used as a reference point and the flat machined as indicated. Ibis is best done with the nulling machine, using a face mill or other large-diameter end mill. Ilie melius at the bottom rear should be cut to match the contour of the lower receiver as closely as possible. This can be accomplished in several ways. Probably the easiest way is tlirough use of a rotary table in the milling machine. Another way is Lhrough use of a radius-cutting or comer rounding, as some call them—end mill. In lieu of either of these, ir can be formed by hand using .i disc, sander. If care is used and the fit is checked frequently, this method will achieve the same result as the others. It will just take longer.
Whichever method is uscdt when the fit is as close as possible, both receivers should be clamped together and the front hinge pin hole drilled.
Before the hole is drilled, however a bushing is turned to fit the lower receiver front hinge pin hole closely, and a 1/8-inch hole is drilled through the center. This bushing is placed in the front hinge pin hole of the lower receiver, and the hole is drilled through the upper receiver hinge block using .i l/K-inch drill. The receivers are then separated and the hole enlarged to full size using a 1/4-inch drill. Ihc purpose of the drill bushing is to protect the soil aluminum lower receiver from damage caused hy use of a full-size drill or
Drill bushings. Drilling front hingK-pin Me
.Shop built upper, damped to com/uerciul tower wilii hashing in Jrwil pin reMly/or drifting.
mutilation From metal chips or shavings.
II the shop-made steel receiver pictured in the Prefect? is used, the drill bushing is not necessary since the hole is drilled through both receivers simultaneously.
If a new commercial receiver or the shop-made receiver is used, or if you have means to remove the recoil spring tube from your existing receiver, a better fit can sometimes be obtained by turning a close-fitting mandrel to fit inside the upper receiver and using a cap and drawbolt to pull i'L U:ic:k tightly iig.dnsl the lower receiver at the rear end before clamping and drilling. With the cross pin in place, the upper receiver assembly should swivel from the closed position
Pi'sfof upper unit r-rady/or mounting to nlmosI a right angle, llic bottom, front, and rear of the mounting block must be shaped to a half round configuration to permit this.
A bracket Lib accept the rear mounting cross pin is made hv welding a 1/2-inch steel cube to the outside surface of a section of I 1/4-inch-outside-diameter tubing. This should have a wall thickness of .065 inch and a length of .fS25 inch to .650 inch. I he side of the cube adjacent ro the Uihing should be radiuscd to fit the tubing closely with the sides and ends angled. The seam, or joint, is built back above the surface by welding. The weld joints -ire then dressed back Hush with the surface and the block width reduced to ,475 inch.
DRILL AFTER ASSEMBLY
BEVEL FOR WELD KG
REAR MOUNTING BRACKET
Upper receiver wiJi rear mounting brücket in place
A slot to accept this block is cut at the bottom rear of the upper receiver to the dimensions shown in Diagram ff2. The slot to clear the hammer can also be cut at this Lime, as well as the magazine opening, including a slot to provide clearance for the ejector.
II' a commercial lower receiver is used, either a relief cut must be made in the left side of the upper receiver to ele^r the holt hold open release button ur the bolt-hold-opcn device must he removed. This cut tan be located by measuring hark from rhe front fare of the receiver as shown in Diagram #1. A simpler method, however, is to position both receivers in their respective assembled positions and mark around the hold-open button, fhe relief cut is not necessary if the shnp-m.'ide receiver is used. Since the 9mm magazine does not extend ro the rear far enough to activate I he bolt-hold-open, there is no point in putting it in the receiver.
With the completed bracket and the front hinge pin in place, both receivers are clamped together, and, using the bushing as before, the mounting pin hole is drilled. Again, the drill bushing is required onlv ii the commercial aluminum receiver is used. As with thr front hole, both receivers are drilled together when using the shop-made receiver. With both pins then in place, a close fitting assembly without any shake or play should result.
An ejection port is machined in the right side, as shown in Diagram #2. I here arc people who will insist that this port need nut be nearly as big as the one shown. They will tell you thai ir is easier for dirt and debris to get into the large port. They do not tell you that it is also easier for dirt and dehris In yet out ol the large* port. I here is also less chance of empty rases striking the edges of the larger port and falling back in the ac tion, causing the gun to jam. I his has happened on numerous oc casions with small ejection ports. Make your choice.
The lengthwise slot, to accommodate the cocking lever, or charging handle, is eur in the left side in a 10:30 o'clock, or 315', position «45 above the centerline) when viewed from the rear. I he 'dog leg* at the upper rear serves as a safety in the open-bolt version. Although it is not required for the closed holt, it will serve as a bolt-hold open if included
A 1/8-inch-wide slot, .200 inch long, must he rut beginning at the front face of the threaded harrel hushing and on the top centerline. The locating pin on the brccch end of the barrel fits into this and keeps the barrel located in its correct position.
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