Lower Receiver

As stated earlier, this book was originally intended to encompass only an upper receiver assembly and magazine adapter, which, when installed on a commercial lower receiver assembly, made possible the pistol caliber conversion. But when it became likely that further manufacture of commercial lower receivers would be prohibited when the so-called "( rime Bill" became law, existing lower receivers escalated rapidly in price. Ihe last time I checked, the asking price Lor one of these had gone from around $60 to more than $400. With this—as well as a probable scarcity—in mind, I decided that a shop-made lower receiver was desirable. The design shown here is intended to conform closely to the commercial configuration and use commercial or surplus parts. Since ii is made entirely of stccL it is somewhat heavier than the original alloy job, hut it is also quite a bit sturdier.

I have attempted to show here bol h a receiver made especially lor the sohraliher conversion unit and one that will accommodate the original full size. military-caliber upper receiver. These differ mainly in the length of the magazine opening and the addition of the bolt hold open device and original magazine latch on the full-size job. Ihe magazine is made just long enough to accept the pistoJ-caliber magazine. a3^d the magazine latch is moved to the lower side and just behind the opening in the same position as with the magazine adapter used with the commercial receiver.

I also used headless screws instead of push pins to hold both receivers together. This not only eliminates the small springs and detents used in the original, but it is more dependable. While disassembv does require a screwdriver and a couplc of minutes of time, it is unlikely that the gun will he rendered dysfunctional due to the push pins being lost, as has happened in the past with the originals.

Construction is begun by cutting the two sheet metal parts from 12•gauge sheet metal to the dimensions shown in the diagrams. Note that two sets of patterns are shown in this chapter. The one is intended for use with the pistol-caliber receiver only and is somewhat simpler to construct than the other, which intended for use in ihe same manner as the full-length-

magazine original.

If the .223 version is used, an offset slot must be formed to clear the raised magazine catch located on the left side of the magazine. Ibis is done by milling a slot .065 inch deep and .710 inch wide in a piece of heavy steel plate. This forms ihe female portion of a form die. With the sheet metal panel located in position over the-slot. a .500-inch-wide piece ol bar stock, used here us a male die, is positioned on the opposite

1.450"

1.450"

Wide Welding Flush

SHOP MADE LOWER RECEIVER SHOWING EJECTOR LOCATION

3/8" HOLES TO BE WELDED FLUSH DURING ASSEM81 Y

Wide Welding Flush

FRONT LOWER RECEIVER PATTERN

REAR LOWER RECEIVER PATTERN

.680"

1.260"

LOWER RECEIVfcR

LOWER RECEIVfcR

Lower Receiver Blueprint

Sheet nielui pans arc cut to sirc and shape

One side folded around form block.

Rear Receiver For Argo

Pn't is reversed in vise ond i}\e vppvzile side /older/.

Part* of rear receiver finer and ¿tocfc mounting bracket

Pn't is reversed in vise ond i}\e vppvzile side /older/.

side of the sheet metal and pressed, squeezed, or hammered until ihe slot is formed. The photographs »hove should clarify this. While the required slot probably could he milled into the side of the magazine well, eliminating the forming

Part* of rear receiver finer and ¿tocfc mounting bracket die process, the remaining metal thickness would only be some .040 inch. I he formed slot will retain its original thickness of .100 inch plus, which will be considerably stiller and stronger, making the extra work worthwhile.

Sheet nielui pans arc cut to sirc and shape

One side folded around form block.

Lower Receiver

LOWER RECEIVER COMPONENTS

STOCK MOUNTING 3RACKET

FRONT HINGr. BLOCK

STOCK MOUNTING 3RACKET

FRONT HINGr. BLOCK

Homemade Trigger Guard Assembly
FRONT : RIGGER GUARD AND MAGAZINE RELEASE HOUSING

GRIP MOUNTING BRACKETAND REAR TRIGGER GUARD

FRONT LOWER RECEIVER PATTERN

Homemade Hammer

Components clomped lo^tiwr for welding.

Weldad info singie unii

Components clomped lo^tiwr for welding.

Weldad info singie unii

Images Homemade Lower Recievers

RELIEVED FOR WELDING

.oOCJ" UN

.oOCJ" UN

RELIEVED FOR WELDING

SlDh

REAR

Diagram

FRONT HINGE BLOCK

Cu o

Cu o

Welding M16 Lower

in rvi

en cr

ct o itj

a in

a in

\ s

/l

yS 1

1

1 1

'J

c cr

Diagram

Ruth sheet melal sections arc damped against form blocks in a lat^e vise and formed wit h a heavv hammer. As I have stated before, the form block should be supported with I docks heLween the vise cross arm and bottom of the form block to prevent the work from bring driven downward below the vise jaws while ¡1 is being formed with the hammer In practice the sheet metal blank is clamped against the form block with the material required to form one side projecting above the form block and vise jaws. Tin: side thus extending iv bent down against the form block. This done, the blank is turned over and again secured in the vise. The remaining side, now extending above the vise jaws and form block, is bent at a right angle as before. Both blanks are formed in the same manner.

The formed blanks .ire positioned at right angles to each other with the top edges even and in a straight line. If the short magazine version is used, three 1/4-inch holes are drilled through each side of the magazine box part, as shown. Both parts are clamped together with the form blocks in place. The vertical seams at the rear of the magazine box are welded, preferably by the TIG process, and the four holes welded shut. Ihese should be built up above the surface and dressed hark flush, if this is done properly, no evidence of the welds will show.

A rectangular block. 5/8" x 7/8" x 1 1/8", is welded to the upper front side to form the front mounting pin base (hinge block). This block should be beveled deeply on the sides adjacent to the front face of the receiver to alJow a heavy, deep weld joint. When this shop-made lower receiver is compared to an original receiver it will be noted that the mounting bracket, or front hinge pin base as it is sometimes known, is quite a bit larger and thicker. Ibis will add a small amount of weight, hut it ako adds quite a lot of strength, making it well worthwhile as far as I am concerned.

A filler block is made up as shown in Diagram r '22 to be welded in place at the rcai of the magazine opening. Ihc longer version is to be used with the pistol-caliber magazines and is made from 7/8-inch material. I he inside has all the metal possible removed to save weight, and the rear purtion is shaped to match the original as closely as possible. I he long maga7ine version is made by welding a plate made frcim I 2-gauge sheet metal across the back of the magazine opening ami welding or silver-soldering a shaped filler block to litis plate. This too is shaped to match the contour of the original as closely as possible.

The welded seams should he dressed smooth and flush with the surface wherever possible, this is done pnor to installing the iiller block at the rear end of the receiver so that the receiver can be mounted in the milling machine without interference from protruding weld joints and the top side milled Hat. Tin: front block is cut back to the magazine opening with a V4-inch radius to match the upper receiver contour. A l/2-ineh slots 5/8 inch deep, is cut in the center of the front block to accept the front mounting pin bracket of the upper receiver. Roth receivers should now fit together closely. If they do not, check for high spots or burrs that are causing the interference and remove them.

liotli receivers are clamped together and the front hinge pin hole is drilled through them simultaneously with a 7/32 (.2l88)-inch drill (after locating and starting the hole with a center drill). I bis is followed by a 1/4-inch drill through one side only of the lower receiver and the upper bracket. The remaining smaller hole is tapped using a 1/4 x 28 tap. This is assuming that you will use the headless screws instead ol pins to hold the assemblies together. Otherwise you should drill the hole completely through with the 1/4-inch drill, install the spring and detent to hold it in place, and use the standard push pin.

A filler block to be installed at the extreme rear of the receiver is cut from 7/8-inch steel plate to the shape and dimensions shown in Diagram ¿22. ilere again, this part should match the contour of the original as closely as possible. As much material as possible should be cut Irom the inside of this part to reduce weight.

A round section, composed of the same material as the bolr(s) were made from» is turned to a diameter ol 1.375 inches and an overall length of 1.350 inches. I he inside is bored to a diameter of .990 and threaded with a 1.065-inch -b>- 16-TPI thread. I his threaded sleeve is then clamped on the top side of the filler block and welded in place. The lop edges of the filler block should ha*e been beveled prior to welding, permitting a deeper, heavier weld joint. 'I he resulting welds must be dressed back flush with the surface before the work proceeds further.

Lower Receiver Blueprint

Magazine rear filler.

1.250"

FRONT VIEW

How Rifling Machine Working

insiiie is bored out iu reduce weight.

TOP VIEW

TOP VIEW

DRILL .217" TAP 1/4x28

DRILL .217" TAP 1/4x28

M16 Lower Receiver Dimensions

REAR

.100"

SIDE VIEW

REAR

.650"

Diegrair i

SIDE VIEW

1

-

.375" "1

GRIP MOUNTNG BRACKET AND REAR END OF TRIGGER GUARD

THREAD 1.87" X 16

THREAD 1.87" X 16

How Rifling Machine Working

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