BUILDING SGN-22 the
By Steven Matthews
Part 1
Matthews is at it again with a series of pieces on building a gun from scratch. This time it’s an inexpensive self-ejecting single-shot .22 rifle he calls the SGN-22.
Ready to try building a gun largely from scratch? Here’s a simple self-ejecting single-shot that’s easy and cheap to build.
I
f you have been a regular reader of SGN for the last three years or so, you have probably read some of my gun build articles. If you’ve built some of them, you have learned a lot about firearms fabrication. You may have thought about going a little deeper into firearms building by actually building a gun from homemade parts rather than using a collection of manufactured components. With that in mind, I recently wrote an article series on building a 9mm semi-auto carbine known as the SGN-9 (4/20/08, 5/20/08, 6/20/08, 7/20/08). The SGN-9 was blowback-operated semi-auto 9mm Luger chambered rifle that featured tubular construction and many self-made parts along with some purchased parts. The skills and tools needed to build it went far beyond what was needed to do a simple kit building project. I thought of it as a good beginning project for those who wanted to advance to actually making their own guns rather than just assembling parts made by others. The SGN-9 project required the use of a lathe, milling machine, welder and a multitude of hand tools. It also required extensive hand fitting of parts. While it didn’t seem all that hard for me, since I have been doing hobby gunsmithing for more than 25 years, it may have been intimidating to firsttime builders. So I decided I should try an slightly easier project. Design Parameters I decided to retain the basic look of the SGN-9, since its tubular construction made it easy to build. I would just scale down the size. I also felt this would make it appealing as a “baby brother” to the SGN-9. I decided to scale the project down to .22 Long Rifle. By utilizing the low pressure .22 Long Rifle round, it would make building easier and more be forgiving on issues of strength. I wanted the action to be easy to build and at first thought a bolt-action would be the way to go. The more I thought about designing a locked breech and rotating bolt action, the more I realized that a straight blowback action would be easier to make.
If the builder had a few of the parts lying around, as many hobbyists do (we all have that drawer full of gun parts!) and really scrimped on finishing, the cost could be very low. If, however, you had to buy everything, the cost would be at the high end of the price range. I had some of the parts so this project cost me about $125. Once I had the basic design and parts selection figured out, I had to figure the easiest way to build the project. I have a well-equipped hobby machine shop, so I can make just about anything, but I wanted this project to be able to be made with the minimum of specialized tools. The methods and tools are what I consider the bare minimum. Many operations and procedures are highly improvised gunsmithing. If you have better tooling and methods, by all means use them. The more tools you have, the easier the project will be. Some may look at features of this project and say there is a better way to do it and they may be right, but I designed this project for those minimum of tools and skill. As far as equipment goes, the minimum needed is a small drill press, arc welder (MIG type preferred), basic home workshop hand tools, a small powered hand grinder like an air grinder or Dremel tool, a good set of dial calipers, and a small hobby lathe.
Magazine feed, however, would make it harder to make, and the original idea was to make it as easy to build as possible. That’s when I got the idea to make it a straight blowback type like an autoloader, but to leave off the magazine to ease the build process. The added benefit would be self-ejection of the fired case. The unlocked breeching system would be very forgiving and the home builder wouldn’t have to worry about the action giving way when the bolt was locked in place and fired if they didn’t build it just right. This is not an original idea. If you read Tom Gaylord’s article on the Wham-O guns (9/20/08 issue), they, along with the H&R Sahara, were self-ejecting single-shots. For the fire control system I decided to use the AR-15 fire control group since it had worked well on the SGN-9 project. I would just scale it down to fit in the smaller trigger housing of the new project. Using a manufactured fire control group would ease the build for those not ready to make hammers and triggers from scratch. This project would require a specialized bolt I’d design myself. This, along with the receiver and trigger housing, would be the main self-made components of the project. The self-made bolt could be made from about $10 worth of materials and would be as easy to build as I could make it. I wanted a readily available barrel that was inexpensive and I found one that fit the bill perfectly. The SGN-9 project cost about $175-$250 to make and I wanted this project to be less expensive. The parts required are minimal: a Ruger 10/22 barrel, an What I came up with could be AR-15 trigger assembly and pistol grip, and some steel built from $75 to $175 depending stock and tubing. This is a very cheap rifle to make. on how frugal the builder was in obtaining the necessary materials.
This job is easier with a milling machine, but Matthews says a cutoff wheel and a Dremel tool will cut the ejection port into the steel tubing that will be the receiver.
Small table-top metalworking lathes adequate for this project are available from suppliers like Grizzly Tools or Harbor Freight for as little as $350, so this project may be the incentive to buy this versatile machine tool. For those who don’t have a lathe and don’t want to buy one, there is an option. A couple of the lathe operations can be hired out and the remainder can be done on the “poor man’s lathe.” You can shape many small items with nothing more than a drill press to spin the parts and some files to shape them. This improvised turning method is a lot of work, but you can get quality results if you have the skill and are patient. I have made many small round parts over the years before I had a lathe with nothing more than files and a drill press to spin them. Since this project would look like a scaled down version of the SGN-9, I decided to name it the SGN-22. Parts Acquisition The first part needed for this project is a barrel. There is one common and readily available barrel that is perfect for this project. The large numbers of hobbyists customizing the Ruger 10/22 with special barrels mean there are many take off/used surplus barrels for sale. At the last gun show I attended before I started this project, there were a half-dozen used barrels to choose from. Prices ranged from $10 to $35.
The Ruger 10/22 barrel should be a tight fit in the receiver tube. You may need to heat the tube for a shrink fit or ream it slightly on the inside. Then pin the barrel.
I found one with a poor exterior finish that was excellent inside for $10. Since I was going to be doing a finish job on this project, the $10 barrel was perfect. The Ruger 10/22 barrel is 18.5 inches long and features a 3/4" smooth shank sized at . 685-.687" diameter. This shank will fit in a 1-inch diameter by .156" wall piece of 4130 chrome-moly seamless tubing quite well. I decided to use this size for the receiver just for that reason. This type of high strength tubing is available from many steel suppliers and also from aircraft suppliers such as Wicks Aircraft. You will need a couple feet of this tubing for this project, but you really should buy extra in case you make mistakes and have to make a part over. It is priced at about $6.50 per foot. For a barrel shroud, I was going to use the same outside diameter, but didn’t want it to be that heavy. The widest part of the 10/22 barrel is .930-.935" diameter and I found that 1-inch by .035" wall chrome-moly tubing would be just about right for the purpose. It would slide right over the barrel at the breech end. About one foot would be right for the project, but luckily I took my own advice and ordered extra. I made a couple mistakes and needed the extra material. This size tubing runs about $3 per foot. For bolt fabrication, I bought a couple feet of 3/4" 4130 chrome-moly rod, also available where you find the tubing. I especially recommend buying extra bolt raw material since the bolt is very easy to screw up and it may take more than one attempt to get it right. You only need a foot for the project but you never know! This rod is about $3 per foot. A faux flash suppressor will be made from a 21/2-inch piece of 7/8" x .120" wall chrome-moly tubing, but any type of steel would be fine if you can find this size. The trigger housing for the SGN-22 will be made from a 6-inch piece of 3/4 x 11/2 x 3/32 (approximate thickness) wall rectangular mild steel tubing that should be available from local structural steel suppliers. A foot or two of this material should only run you a couple bucks. A couple feet of 1/2 x 3/16" flat steel will be used to make part of our stock. It should run you less than $1. The buttplate can be fabricated out of a 6-inch piece of
The barrel shroud is made from 4130 thin wall tubing. The hole size and spacing is up to you, but use a drill press and vise to keep the holes aligned and spaced.
Plug weld the shroud to the barrel itself, then weld it to the receiver tube to fill the joint. Use several small welds with cooling time between them to avoid overheating.
11/2 x 3/16" flat steel, also priced under a dollar. I used a couple pieces (one piece of 3/4" rod and one piece of 1/2" flat stock) of scrap aluminum that I bought at the scrap yard for a couple dollars to make the faux magazine and the recoil spring plunger. Since the magazine is fake, you could make it out of anything you want-wood or plastic or even steel if you don’t mind the weight. You will also need a couple more miscellaneous pieces of steel and some screws and pins. To ease the build process, I used several factory-made parts. I got several DPMS-made AR-15 parts from Brownells, an excellent source for gun parts, both original equipment and custom. You need these AR-15 parts for this project: hammer, trigger, disconnector, the springs for these parts, safety/selector lever, firing pin, pistol grip and two hammer/trigger pins. These parts can be bought individually, but it’s usually cheaper to by one of the sub-assembly parts kits and save the leftover parts for future projects. A few of the other parts can also be obtained from Brownells. I used a Weaver #81 scope base to attach a scope and vertical foregrip. Since this rifle features a straight-line stock, I used tall extension scope rings to raise the scope high enough. I also selected a Pachmayr RP250 black recoil pad. Since my eyes aren’t what they used to be (getting old stinks!) I ordered a compact 4X scope from SGN advertiser CDNN . This imported scope was only $18. Disclaimer Before we get into the actual building of this project, it’s time for the customary legal disclaimer since I am just a hobbyist gunsmith and am simply documenting my own amateur efforts. This article is not a step-by-step build tutorial. It
This should not discourage potential builders, it’s all part of learning gunsmithing. One learns very little by just reading an instruction sheet that says place part B into slot C followed by part A. That is simply “assembling,” not building a gun. When you make, fit and modify your own parts you become intimately familiar with your project and are learning gunsmithing skills far beyond a simple assembly job. This learning process has inherent dangers associated with it since firearms are sometimes dangerous items. You must accept and understand the hazards involved in building and using firearms. If you do not understand what you are doing you will be putting yourself at risk and you should not do this project. Neither SGN/ Intermedia or the author assume any responsibility for the construction, use, legality or safety of your self-made project. It’s your project and you, the builder, assume full responsibility for your own project.
Drill rows of holes in a length of tubing, then file out the remainder to make a muzzle brake. It then can be silver-soldered to the barrel after removing the finish.
will only cover the high points of the build process. I will give some general dimensions and procedures, but the builder will have to supplement the project with his own gunsmithing skills and knowledge. As in any self-built project there will be builder-induced variations or mistakes that will have to be compensated for. If one part is made slightly out of spec. another part may have to be heavily modified to make the project work correctly. This is part of the “art” of gunsmithing. Hand-made parts by their very nature generally need to be hand-fitted for proper function.
The recess for the cartridge head must be precisely located in the bolt face. A lathe is best, but a drill press will do. Drilling to the proper depth is critical.
Receiver Fabrication and Barrel Installation The receiver of the SGN-22 will be made from 1-inch by .156" wall 4130 seamless chrome-moly tubing. You will need a piece about 20 inches long. This is slightly overlong, so that when the project nears completion, you can cut the receiver/stock to the preferred length of pull. Be sure to square the ends after cutting, since you will be measuring from the ends. While the specifications for this tube would indicate an internal diameter of .688", there are manufacturing tolerances to consider. Your actual size may vary a couple thousandths from the stated size and this will need to be compensated for during building. The first step is to cut an ejection/loading port in the receiver tube. This cutout needs to be large enough for the user to comfortably insert a cartridge. Since I have fat fingers, I made this port roughly 13/4 inches long by 11/16" wide. I located it about 3/4" back from the front of the tube. This will result in the rear of the barrel being just about even with the front edge of the port. This port can be cut out with a milling machine or by hand with a Dremel type tool with cutting disc. Once cut, smooth up all edges. The barrel can now be installed in the front of the receiver tube. The shank of the barrel needs to fit snugly into the tube. Manufacturing tolerances in the barrel and tubing mean your barrel may fit just right or be too loose or too tight. Mine was a little loose, since my tubing measured .687" and my barrel shank was .685". To get a snug fit, I had two options: either shim the shank with .001" shim stock or shrink the tube. I chose to shrink the tube diameter a couple thousandths. This is easily done by placing the end of the tube in a vise and lightly clamping it in place. One side of the last 3/4" of the clamped tube was heated red hot with a torch. This heating expands the tube wall and since it is clamped, it can’t expand and therefore swells slightly and thickens. When the tube cools, the wall contracts, and since it is now slightly thicker, the diameter is slightly reduced when cool. This is only a few thousandths of an inch but that is all that is needed on this project. This brought mine to a good snug fit. This isn’t a real precise method, but it does work. If it shrinks too much, file, ream, grind or sand it to the right size. If, on the other hand, yours is too tight to begin with, you will just have to file your barrel shank a little smaller or open up the tube diameter a little by grinding, filing, etc. You can also just lightly heat the tube with a torch to expand it,
A milling machine makes cutting the hammer slot in the bolt a lot easier, but you can do it by drilling a series of holes and filing out the spaces between them.
then insert the barrel while the tube is hot, When you insert the barrel into the receiver tube, you will need to index the barrel to locate the extractor groove in the right place. Install your barrel so that the extractor notch in the face of the barrel is about 1/8" above the bottom edge of the ejection port. This should leave adequate clearance to keep the ejected case from striking the receiver when being ejected from the gun. Once the barrel is in the correct position, the barrel needs to be locked in place. I pinned my barrel in place by drilling a 5/16" hole through the receiver wall and about .100" into the barrel shank. Be sure you don’t drill too deep and drill into the chamber. I tapped in a tight-fitting pin and then cut it flush with the receiver and welded over it to permanently lock it in place. I then ground it flush to the receiver tube. I also used the barrel shroud installation the further to lock the barrel in place. I made a ventilated barrel shroud out of a 7-inch piece of 1-inch by .035" wall tubing. The hole size and spacing can be to your preference. My tubing was a little undersized, so I had to reduce the barrel diameter slightly to get the shroud to slide over the barrel. At the rear of the shroud, I drilled two 5/16" holes on opposite sides so I could plug weld the shroud to the barrel. The shroud was slid over the barrel till it was about 1/8" from the front of the receiver. This thin groove will be a weld groove. Before doing any welding, be sure your shroud is oriented correctly so the holes look good. Also be sure the barrel is centered in the shroud. You don’t want your holes to be running off at odd angles or have uneven gaps between the barrel and shroud. Plug weld the two holes to secure the shroud to the barrel. Use only enough weld heat to lightly penetrate the barrel and allow it to cool before you do the other hole to keep heat down. Now weld the shroud to the front of the receiver tube. Weld in the groove and use enough weld heat only lightly to penetrate the barrel surface. Only weld about a half-inch at a time and allow for cooling before doing more welding. After welding, grind down all the welds smooth with the receiver and shroud. The shroud is now attached to the barrel and to the receiver, so this is further locking the barrel to the receiver tube. This, along with the pressed-in pin, is more than adequate for a rimfire. Next month (4/20 issue): Building the bolt.
