Table Of Contents

Materials and Tools • 1 Upper Receiver • 9 Bolt • 17 Barrel -25 Barrel Shroud, Stock, and Grip • 31 Sights • 41 Lower Receiver • 5 i Magazines • 73 Small Parts • 83 Filling and Assembly • 95 Heat-Treating and Finishing • 99 Firing and Adjusting • 103


11 my memory serves me correctly» it was in early 1980 that someone suggested lu ine that a Mrnrn conversion unit to mate with and mount on aci AR-15 ur M16 lower receiver assembly would be desirable. A hit of research on my pari indicated thai there was indeed a market For such a conversion»

At the time I thought it best to use square tubing for the upper receiver sincc it was possible to get more weight inlo a square boll of the maximum permissible len&tli than a round one. A bushing whs welded into the front end of the receiver tube and ho red and threaded to ac:c:ept a removable barrel. This was held in place by a barrel-retaining nut that screwed on to the barrel bushing against the flanged barrel, holding it securely in place, litis same method is used on the version described in this book.

1 made up a magazine adaptor, which not only reduced the size of the magazine well to just accept a 9mm magazine (1 used Slen magazines) hut also served as a mounting bracket for the ejector and housed the magazine latch. A combination earning handle and rear sight assembly was formed from sheet metal and welded in place to match a surplus M16 front sight assembly obtained Ircirn one: of the surplus military parts companies that flourished ai I he time.

After some slight modifications and adjustments the assembled rifle, or carbinc as

Spring Recoil Brackets
5mm piM'ol version. Alude in the early JVtttte. Hi/Ie version with folding stock from same period.


some would call it, performed quite well (well enough, in lact, thai I managed to sell one to almost everyone who tried it). These were made in both 9mm and .45 caliber.

Since the bolt and recoil springs were completely housed in the upper receiver rather than extending back into the liuttstock as the original parrs did. these units were adaptable to folding stocks as well as pistol versions.

At that time there were several companies manufacturing lower receivers lor these guns. Ihese were intended, as now, to be used with military surplus parts to assemble AR-15 or M16 rifles. They ranged from excellent quality to pure junk One such gun. which was equipped with .1 cast aluminum receiver, was accidentally knocked over onto the floor from a leaning position against the wall and broke into two parts. Naturally, I didn't use any more of or install my parts on them, In addition. I soon discov ered that dimension % varied considerably between the various brands especially the magazine openings.

This did not actually present a problem as long as I was dealing with lower assemblies belonging to local customers. Ihey brought them to my shop arid 1 assembled the units, fitting the parts as required. The only trouble I experienced was with one would-be customer. This punk was a native of New York City, come down to our part of the country to enlighten us poor, ignorant hillbillies as to how the outside world behaved. He was one of these people who talked all the time, and when he did let anyone else get in a few words he didn't hear anything they said since his mind was occupied with what he was going to say next. This guy bought several of these units from me and ruined even' one of them. In spite of what I told him to the contrary, he tried everything he could think of to modify tlieni to fire full automatic and otherwise "improve" them. I finally got all I could stand of him and ran him off. He

Photo Ar15and M16 Lowers
FulMcngtf* view showing una mounted on Colt-made lower.
Expedient Firearm
Mounted 0/1 shop made receiver.


Although ar the time this book was written il was perfectly legal for an individual to manufacture a firearm for personal use. experimental purposes, or research and development, it is likely that new laws have been added since. Il i* probably still legal for the upper receiver assemblies described in this book to be built ami assembled on an existing lower receiver. However, if the lower receiver, as described herein, is used, an illegal firearm will result. It is die readers obligation to carefully research all pertinent laws before any such construction is attempted.

Technical data presented here, particularly data on ammunition and on the construction, use, adjustment, and alteration of firearms, inevitably reflects the authors individual beliefs and experiences with particular firearms, equipment, and components under specific circumstances ihai ihe reader cannot duplicate exactly. The information in this book should therefore be used for guidance only and approached with great caution. Neither the author, publisher, nor distributors assume any responsibility for the use or misuse of information contained in this book. Thh book is presented for academic stiuly only;

call me everv loul name lie could think of. eventually telling me that the unit I sent him wasn't worth a damn. When I finally managed to get in a word. I asked him if he had read the instruction sheet.

"To hell with any instruction sheet," he retorted. Tin a federally licensed gunsmith, and I don't need an instruction sheet. The damn parts don't Pit.M

Ahout this time 1 lost my temper too. and I proceeded to inform him that possession nf a federal firearms license was not an indication of either intelligence or ability 1 told him that most of the names he had called me not only applied to him too, but his mother and wife as well. 1 his got his attention, so I told him I would send along another, slightly smaller magazine adaptor and another instruction sheet, which I insisted lie read. To his credit, several days later I received a letter from him stating that he had made it work and apologizing for his previous conduct.

But such incidents happened too often. It took too much time to straighten out the problems, which were not my fault in the first place. I turned the entire operation over to a friend of mine and went on to other things.

Several years later I designed and built a few of the round-reeeivered versions similar to those described in this hook. These were made in both lJmm and .45 versions and included the open-bolt

Open Bolt M16 Lower

9mni conversion (pUto/ version).

-'h>- KACh pistol version described herein. This open-bolt version has interchangeable trigger parts that pivot on the same cross pins ¿in the original parts and will fire both as a full or semiautomatic. 1 made and sold several of these, but after a time— even though I was only furnishing parts I became concerned about their legality and discontinued them as well.

Several months ago. as I prepared to put this book together, I built a nen upper receiver assembly and a magazine adaptor in the rifJe version that used the standard lower receiver assembly. 1 also built a nen open-bolt pistol assembly using my own parts in rhe trigger mechanism as before. These were fabricated primarily for photographic purposes, to use in illustrating this book. These parts included several slight improvements (?) over the older versions and functioned quite well when atLached to a standard lower receiver.

Then, just about the time 1 was putting the finishing touches on the book, another setback occurred. Congress passed the so-called "Crime Bill" of 1904. and suddenly lower receivers, which had been selling for $60 to $80 each, skyrocketed to an asking price of more than $4(K). Even worse, no more can he produced.

Realizing the problem this would cause if the time ever came when one was compelled to build such a gun or remain defenseless, I went back and designed and built a substitute lower that is made using formed sheet metal with wcldcd-in gussets and ends. The result is actually quite a bit sturdier than the original, although heavier. It dues, however, provide an alternative that will allow the builder to construct the entire gun from raw materials.

The guru then, as described in this book, can In- built as either a rifle or pistol, open or closed holt, semi- or full automatic, and with either a self-contained bolt and recoil spring assembly ur a heavier bolt that uses the original recoil spri ng/bi ilfer assembly.

As things stand at present, it is likely that any version of this gun would be illegal if manufactured in its entirety. However, if the c losed-bolt version of the upper receiver assembly is used with an existing lower receiver, it would probably be considered a legal gun. Just how this makes either version any more or less lethal and dangerous than the other is beyond me. But the dimwits we pay to dream up such rules seem to think that those, laws will, in some fashion, reduce crime.

It is strongly recommended that readers carefully research all laws concerning building or possessing such a firearm before finishing and assembling the gun. Unfinished parts are not supposed to be illegal, but this too may change. Rc careful.


Sheet metal, as used in this project, can usually be obtained locally, lhe 12-gouge material can, as a rule*. he lountd in sheet metal shops and metal fabrication plants If possible, try to get the type with h rolcl finish, eommonly known as "cold rolled/' This will have a bright finish as opposed to the rough black finish of the "hot rolled" type. Il 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 il elsewhere, material cut from ulder automobile or light tniek frames ean 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 better material than c ommon sheet metal.

Leaf springs from cars or light trucks can be used lor Hal stock material, and axlrs Irom lhe same source will provide round stock. Valve stems salvaged from four-cycle engines, as well as shuck absorber shafts, can be used for 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 mv other books. If a bluing setup ts available, material can

Magazine Band BushingMagazine Band Bushing
A metal-culling band som- will save a let ofrüy.jw graue.

\ heavy vise eon be OStfd os n press broke lojonn sheef mitai parts among othe* uses.


M16 Barrel Machine Drawing






M79 Receiver Drawing


front end of I lie 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 bushing will have a finished diameter of .875 inch, it should hi' kept smaller and bored to si/e after the bushing is welded in placc. Ihe bushing should be positioned inside the receiver with .600 inch extending back into the receivei and sccurcd permanently in place by welding through the loui holes and building the welds up above the surface far enough thai they can be 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 1/2* is likewise welded in placc on what will be the exact bottom ccntcr of the receiver blank. It should be relieved on all four sides where it joins the receiver and builr hack up above the surfacc with weld material and machined back flush. The forward edge should be Hush with the receiver face.

Ihe assembly is now chuekcd in the lache and the barrel bushing bored to .K75 inch. There should he .500 inch of the bushing extending past the front face of the receiver. This is turned to a diameter of 1.1 25 inches and threaded 24 threads per inch.

For 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 side of the upper receiver. The ccntcrline of the front hinge block is used as a reference point and the flat machined as indicated. I bis is best done with the milling machine« using a face mill or other large-diameter end mill. Ilie radius at the bottom rear should be cut to rnaieh the contour of the lower receiver as closely as possible. This can be accomplished in several ways. Probably the easiest way is through use of a rotary table in the milling machine. Another way is Lhrough use of a radius-cutting or corner rounding, as some call ihem—end mill. In lieu of either of those, ir can be formed by hand using .i disc sander. If care is used and the fir is chocked frequently, this method will achieve the same result as the others. It will just take longer.

Ildrrcf bushing end from hinge hiiw h are vw/ded in pii*cc
M16 Lower Receiver Milling Blueprints
VV'Vidi / ig con 11 I

Whichever method is used, when the fit is as close as possible, both receivers should be clamped together and the fronr hinge pin hole drilled.

Before the hole is drilled, however, a hushing 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 placcd in the front hinge pin hole of the lower receiver, and the hole is drilled through the upper receiver hinge block using a I/R-inch drill. The rcccivcrs are then separated and the hole enlarged lu full size using a 1/4-inch drill. I he purpose of the drill bushing is to protect the soil aluminum lower receiver from damage caused by use of a lull-sizc drill or

Tji Hole Chart
DWlImg jrrjMÎ htrigK-pip liofe
Tji Hole ChartTji Hole Chart

Shop-built upper, cfarnpou lo com;ui>r<;itiI lower vv/tJi hashing in Jrwtl pui Tuile, warty for dril'tag.

mutilation From metal clups or shavings.

II the shop-made steel receiver pictured in the Preface 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 rube 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 eap and drav\bolt to pull ¡L l>:tc:k tightly Hgninsl i he 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'srôf upper unit, reach/for mounting.

to almost a right angle. Ilic bottom, front, and rear of the mounting block must be shaped to a half round configuration to permit this.

A bracket Lo accept the rear mounting cross pin is made by welding a 1/2-inch steel cube to the outside surface of a section of I l/4-ineh-out side-diameter tubing. This should have a wall thickness of .065 inch and a length of .fS25 inch lo .650 inch. The side of the cube adjacent to the tubing should be radiuscd to fit the tubing, closely with the sides and ends angled. The seam» ot joint, is built back above the surface by Welding. The weld joints are then dressed back flush with the surface and the block width reduced to .475 inch.

.250" DIA


Upper Receiver Diagram
Lower Receiver Dimensions




Lower Receiver Dimensions

Cut near center to dear bolt release.

Side Diagram Lower
Completed receiver assembly.
Magazine Release Assembly

Lpper receiver with rear mounting bruiiccl i/i place

A slot to accept this block is cut at the bottom rear of the upper rcccivcr to rhe dimensions shown in Diagram ff2. The slot to clcar the hammer can also be cut at this Lime, as well as the magazine owning, including a slot to provide clearance for »he ejector.

II" a commercial lower receiver is used, cither a relief cut must be m ule iri the left side of the upper receiver to ele^r rhe holt hold open release bulton or (he bolt-hold-open device must be removed. This cut can be located l>y measuring bark from rhe front face nf the receiver as shown in Diagram ft 1. A simpler method, however, is lo position both receivers in their respective assembled positions and mark around the hold-open button. The relief cut is not necessary if the shnp-made receiver is used. Since the 9 mm magazine docs not evtend ro the rear far enough lo activate I lie bolt-hold-open, there is no point in pulling it in the receiver.

With the completed bracket and Lhe 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 the 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.

Barrel Schematic

Shi is cut /or barrel-positioning pin

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 yon that it is easier for dirt and debris to get into the large port. Thcv do not tell you that it is also easier for dirt and debris to gt%t out ol I he large port. I here is also less chance of cmptv rases striking the edges of the larger port and falling back in the action, causing the gun to jam. I his has happened on numerous occasions with small cjcction ports. Make your choice.

The lengthwise slot, to accommodate the cocking lever, or charging handle, is cut 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 bolt, it will serve as a bolt-hold open if included

A 1/8-inch-wide slot, .200 inch long, must be c ut beginning at the front face of the threaded barrel hushing and on the top centerline. The locating pin on the breech end of the barrel fits into this and keeps the barrel located in its correct position.

+1 0


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