Barrels

Obtaining a suitable barrel is relatively easy at this time, but this situation could change for the worse in the near future.

.22 barrel blanks are readily obtainable from any of the barrel manufacturers. And most gun shops sell used .22 rimfire barrels at a cheap price. A 3V4 inch section of barrel is all that is needed for these plans.

The .32 ACP jacketed bullet usually measures .311 -.312 inch, which means a barrel with a groove diameter of .311 inch will serve nicely for the .32 ACP. A rifle barrel from a .303 British, 7.65 Belgian (or Argentine) Mauser, or 7.7 Jap are of the proper correct groove diameterto serve beautifully for the .32 ACP.

As with the .32, the .380 designation does not indicate this load's exact bullet diameter. Like most other .38's, the bullet actually measures .355 inch. So any barrel intended for the .35 caliber rifle cartridges—the .357 magnum, or 9mm Luger—is suitable for use as the barrel for the .380 pistol.

While many commercial .380 pistol barrels have a groove diameter as large as .362 inch, the use of bullets larger than .355 inch is usually not possible. A larger diameter bullet will bulge its case to the extent that the cartridge will not even enter the chamber. So nothing is gained by having a groove diameter larger than the .356 -.357 inch, which is standard in commercial barrels.

The internal dimensions of .22 caliber barrels and commercial barrels are usually fairly consistent. Military rifle barrels vary considerably, so it is a good idea to "slug" any such barrel before you use it, to determine its exact groove diameter. Do this by first finding a lead slug slightly larger than the groove diameter of the barrel in question. Drive the slug through the bore from chamber to muzzle, using a blunt-ended rod. Catch the slug as it is pushed out the muzzle end, or let it fall on something soft. Dropping it on a hard surface may deform it, spoiling any chance of an

3.500"

BARBEt ASSEMBLY

Brevete Pistol

Above: barrel with front and rear retainers disassembled. The rear retainer in particular must be tightly fitted; otherwise the pistol will shoot inaccurately, due to "play" between the receiver and the barrel retainer(s).

Below: barrel with front and rear retainers screwed in place. The front retainer is checkered for easy removal and appearance.

accurate measurement. By carefully measuring the slug with a micrometer or vernier caliper, the barrel's exact bore and groove diameter can be determined.

Also, the rate of twist of a prospective barrel can be easily determined. Insert a tight-fitting brass brush or a patch through the slotted end of a cleaning rod, and push it into the barrel's bore. Make a mark on one side of the rod, then push or pull it through the bore until the mark on the rod rotates one complete turn, measuring the distance that the rod travelled to complete one revolution. This figure will indicate the barrel's rate of twist.

In other words, if you moved the cleaning rod ten inches to cause one complete rotation of the mark, your barrel has a twist of one turn in ten inches.

If you accept the advice of certain "experts," finding a barrel with the proper rate of twist could present a problem.

Why? Because they believe that heavier bullets require a faster rifling twist than lighter bullets of the same caliber. Also, consider that the heavier bullet usually has a slower velocity than its lighter counterpart. These experts warn that a too-rapid rate of twist will result in bullets that spin erratically, or "yaw."

Checking a gun data book shows that the .22 long rifle, .32 ACP, and .380 ACP all "require" a rifling twist of one turn in 16 inches. But of the three, only the .22 barrel is readily available with this specification. All of the military surplus barrels previously recommended for the .32 ACP or .380 ACP have a rate of twist less than one in 16 inches, with a few exceptions. This means that one must either order this barrel especially from a manufacturer, or rifle it personally.

But before you go to the trouble, refer back to the data book's handgun section. Now let's make some interesting comparisons between the ACP's and Lugers.

The statistics show that the .32 ACP with its one in 16 barrel uses a 77 grain bullet which travels at 900 f.p.s. The .30 Luger, on the other hand, uses a heavier 93 grain bullet travelling at a faster 1220 f.p.s., but has a barrel twist rate of only one in 9.85 inches! Statistics also correspond similarly between the .380 ACP and 9mm Luger.

These figures suggest that the military surplus barrels suitable for use in the .32 ACP/.380 ACP designs presented here might work well after all. And this proved to be the case.

For my own .32 ACP barrel, I used a piece from a 7.65 Argentine Mauser barrel. It has a twist rate of one in 9.8 inches. My .380 ACP barrel is a section of .35 caliber commercial barrel, with a twist rate of one in 12 inches. Standard Remington 513T rifle barrel is used in my .22 pistol.

After my three home-made pistols were finished and assembled, a group of seasoned handgunners and I test-fired them for accuracy. At the same time, we also test-

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BARREL CALIBER MEASUREMENTS

fired some comparable commercial pistols. When the tests were completed, we found that my home workshop guns were at least as accurate as the commercial models, and in some cases, even more accurate. I attribute this to the fact that the barrel and sights on my pistol design remain stationary, while the others did not use this design feature.

In the event that you cannot obtain a suitable length of barrel, or you feel that you must have a rate of twist that is not at hand, it will be necessary to bore, ream, and rifle your own barrel.

One point I will repeat is that you must use the best steel possible for your barrel. Military rifle barrels are still probably the best source for your barrel, even though it will be reamed to a larger size and rifled with a different twist.

Surplus 7mm barrels can readily be reamed and rifled for the .32. Any of the .30, 7.65, 7.7, or 8mm barrels can be reamed and rifled to the proper dimensions for the .380.

Lacking suitable barrels to rework, you will have to make your barrel from "scratch"; i.e., a good quality piece of steel rod. Car and truck axle lengths are likely sources for good quality steel of this type, as are steering sector shafts, transmission shafts, and others. Don't try to use iron bolts or similar hardware. A weapon constructed from such material would present a definite safety hazard.

Sufficient instruction is given in these volumes to enable anyone capable of drilling, reaming, and rifling a useable barrel to do so. A couple of extra tips on this process follow.

First, since the finished barrel for the autoloading pistol is only 3Vi inches long, extremely long shanked drills and reamers are not required to make it. Barrel blanks should be at least four inches long, to allow any "bell mouth" to be removed when the barrel is finished.

When drilling a barrel blank, either from an undersized surplus barrel or a completely new one, always start with undersized drills and reamers and enlarge this bore by using progressively larger diameter drills and/or reamers. For the .32 ACP barrel, an "M" drill measuring .295 inch is the largest drill used if a reamer of the correct bore diameter (.303 inch) is available. The "M" drill is followed by a 19/64 inch reamer which should ream the bore to .2969 inch (or .297 inch). But that is still .006 inch too small, so another reamer must be found for the next step. If no such reamer is available, an "N" drill will bore the diameter to .302 inch. Finish by giving the bore a careful lapping to remove tool marks left by the drill to produce a satisfactory bore of .304 inch to .306 inch in diameter.

For the .380 barrel, an 11/32 inch drill having a diameter of .3438 inch (or .344 inch) is the largest drill used, and is followed by a .350 inch reamer. Here again, if no reamer is available, an "S" drill will bore it to .348 inch. Lapping then increases the bore diameter to the required .350 inch, or slightly larger.

Finally, I again stress the importance of using sharp, properly-ground drills and plenty of lubricant. Be certain to feed any drill into the bore very slowly, using a tail-stock chuck in the lathe. Otherwise, the drill will make the bore oversize to begin with. If this is the case, you might as well start over, using the proper techniques as stated, and measuring carefully until the proper bore diameter is obtained. The barrel is rifled as described in Volume One.

After the barrel is rifled, the outside is turned to a smooth-finished diameter of 9/16 inch (.5625 inch), and cut to the finished length of 3Vi> inches. Both ends are then threaded, either with a suitable die, or by cutting the threads in a lathe. The breech end is threaded the same, except to a length of .500 inch. These thread dimensions and the outside diameter of the barrel are used simply to enable the threading to be done easily with a pre-manu-factured tap and die set. On the other hand, if the threading is done with a lathe, these dimensions can be varied to suit you. Do not reduce the diameter of the .380 barrel much. The thicker it is, the better.

A muzzle cap or barrel retainer is made from one inch O.D. round stock to the dimensions shown, and threaded to screw onto the barrel's muzzle. A retainer is also made at the same time to thread tightly onto the breech end of the barrel. First, turn a single piece of stock (for both retainers) to the correct outside diameter. Bore this piece with a 27/64 inch drill, then thread it with a 9/16 * 18 tap. One end of the piece is knurled, since it will be the muzzle cap. A lip is cut in the muzzle cap to fit inside the slide body, as shown in the diagram, and any excess steel trimmed off. Cut the breech end retainerto length from the remaining rod, and screw it tightly onto the chamber end of the barrel. The sides of this retainer are cut to the size and shape shown in the diagram. The muzzle end of the barrel should be smoothly finished, and its inside edge rounded slightly or crowned.

Obtain a finish-chamber reamer ground to the proper dimensions for the desired caliber. A chamber is cut in the breech end of the barrel deep enough to allow the breech block to just contact the breech end of the barrel, with a maximum length cartridge case or headspace gauge in the chamber. Round the lower edge of this chamber slightly to allow cartridges to feed smoothly into it from the magazine.

Suitable chamber reamers are available from reamer makers such as the Clymer Manufacturing Company and several others. Reamers can be made by turning drill rod to the dimensions shown for each caliber, then grinding and filing the body of this reamer blank to just under half diameter. After properly hardening and stoning its flat side as smooth as possible, the home-made chamber reamer is finished. Since it has only one cutting edge, it must be used slowly and carefully. But it will cut a serviceable chamber.

To complete the barrel assembly, find or make a recoil spring with an inside diameter of sufficient size to slip freely over the barrel, but small enough to fit inside the slide body, again without binding. Presently, suitable recoil springs are available at hardware stores. If this situation should change, suitable springs can be wound as described in Chapter Three. Wind the .380 spring from .0425 inch wire into 14 to 16 coils with an uncompressed length of 3 inches - 31/« inches. Springs for the .22 and .32 can be somewhat smaller and lighter.

I suggest that you start with a spring that is longer than necessary, then cut to proper working length after test-firing the gun.

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  • Faramond
    How thick does a .380 barrel need to be to be threaded?
    2 years ago

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