Rifle Chamber Insert (Converts rifles to fire pistol cartridges)

By Andrew Willis


Rifle Chamber Insert
Illustration courtesy of The Sportsmen's Guide.

The catalog and Internet company Sportsman's Guide sells a steel cartridge adaptor that lets you fire .32 APC pistol cartridges in your .30-06, .303, or .308 Winchester rifle. This sounded like an interesting thing to try and so, for $14.97 plus shipping, I soon had a cartridge adaptor for .308 Winchester to play with.

The way this thing works is probably self evident from looking at the picture above. What you do is place a .32 APC cartridge in the end of the adaptor. The adaptor is then single-loaded into your rifle for firing. The .32 APC pistol bullet diameter of .311 is close enough to the normal .308 rifle bullet size that it goes through your rifle barrel with no problems. You will normally need to use a pencil to push the spent 32 APC cartridge out of the adaptor base. It does not require much of a push and sometimes they fall out by themselves.

To use the adaptor you will probably need to adjust the adaptor length to fit your chamber by sanding the head with emery cloth, as directed by the instructions enclosed with the adaptor. I used a small square of 120-grit emery cloth. What you do is hold the emery cloth on a hard smooth surface. Then, place the head of the adaptor on it and sand the end using a circular motion. Check it occasionally in your rifle action until the action just closes easily. I suggest you try to remove the circular swirls on the head end before firing it in your rifle by using a finer grade of sandpaper than I did. I believe that swirl marks left on the end of the adaptor were transferred to the end of my bolt during firing.

Even if you have something other than a single shot, you will still have to load and fire the pistol cartridges as you would with a single shot rifle. The pistol round does not have enough power to cycle semi-auto rifles and the pistol cartridge can easily slide out of the adaptor. If you tried to load several adaptors and load them into your magazine, a pistol cartridge would likely fall out while cycling, since the .32 APC cartridge has an easy slip fit in the adaptor. In addition, since the adaptor is shaped like an empty rifle case, it lacks a rounded bullet shape at the end that most guns rely on to guide the cartridge into the chamber.

Finally, you want to avoid the rifle's action throwing your 15-dollar-plus adaptor off into the weeds or onto a hard surface. I let mine hit the concrete once and the cartridge mouth was slightly bent. It straightened out with the next shot, but I concluded that I needed to catch it with my hand as it came out of my rifle's action.

The Sportsman’s Guide product information page says, “If you have a .308, .303 or .30-06., you can make it more 'town-friendly', and practice shoot it for less.” It goes on to state, “The gun becomes low recoil and low noise (similar in volume to a magnum air rifle).”

I disagree with the noise statement. When I fired a Remington UMC practice cartridge, the noise sounded like a regular .22 LR rifle cartridge. I think that the .32 adapter is too loud to be called “town friendly.” Since I had been interested in some quiet backyard shooting, I did some test reloading of .32 APC shells to find out at what point they did become quiet. What I discovered was that I could put no more than 1 grain of Clays powder under a 71 grain metal case bullet fired from my 22" barrel. The average bullet velocity was 637 fps.  At that point, the sound was more of a loud pneumatic blast that lacked the “crack” typical of supersonic bullets. I also tried using a 49 grain “O” buckshot pellet as a projectile, but it lacked the weight necessary to obtain good combustion and the exiting muzzle gasses were louder and had something of a supersonic crack with the same powder load.

Typical muzzle velocity from a pistol for my factory test Remington UMC cartridge is 905 fps according to Remington. The average muzzle velocity from my rifle was 1095 fps. Pistol cartridges are meant to fully combust in pistol length barrels, so the 22" rifle barrel only added around 17% more velocity.

The adaptor detracted from the rifle's accuracy. Typical five shot group sizes at 25 yards measured from 1-½” to 2-¼” using a 71 grain FMJ bullet. That was a little disappointing, as my normal 150 grain .308 Winchester hunting reloads typically shoot ½” three shot groups at that distance. These groups were all fired while sitting at a picnic table and holding the rifle with my elbows rested on the table. 2-¼” group accuracy is bad enough that I would hesitate to use this adaptor for squirrel hunting. I would certainly not go for the head shots that would be normal when using a .22 LR rifle. The point of impact shifted to the right a couple of inches from the settings normal for my deer hunting load, but this is to be expected when changing loads.

Sportsman’s Guide only sells the most popular size cartridge adapters. However, MCA Sports sells 34 adaptors for a variety of .22, .30 and .32 pistol cartridges fired in various rifle cartridges. Incidentally, the Sportsman’s Guide calls this product an "insert," while MCA Sports calls it an "adaptor." I think the adaptor term is more accurate.

Whatever you call it, this device has limited usefulness. Accuracy is reduced and handgun cartridge cost is much higher than plinking with .22 LR cartridges. It could possibly be used for introducing a youth to a larger rifle with negligible recoil if you cannot (or don’t want to) handload low recoil cartridges. However, since the rifle's operation would be as a single shot only, that does not seem like a good training tool. If you want low noise for backyard plinking or pest control, CCI .22 Short or LR CB or Remington .22 LR CBee cartridges seem like a better way to go for less money, more convenience and greater accuracy.




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Copyright 2009 by Andrew Willis. All rights reserved.



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