Caliber Conversions

[PzGren]

I have always been fascinated with caliber conversions to switch from centerfire to rimfire.

I have a revolver conversion that changes .357/.38 caliber revolvers with 2 to 6 inch barrels to .22 l.r. Accuracy isn't bad but POI is drastically changed.



I have a Colt conversion unit with the floating chamber that is only marginally accurate and the floating chamber gets very dirty, even with copper plated ammo. It is a complete upper with its own extractor / ejector in simple blowback design and a reduced power recoil spring.



I also have a .22 conversion for the Swiss P210s. The quality is excellent, as can be expected from SIG. The slide is lightened and the ejector is located on the top of the magazine. Accuracy is pretty good.

Finally, we get to the Walther P38/P1. When Walther developed the conversion, they decided to use a barrel insert, that fits into the standard 9mm barrel, which has the locking block mounted to it. The slide was lightened and the conversion was cut inside, so that the locking block could not engage. The front of the slide has a cut out on the bridge to easily identify it as a .22 conversion. The ejector is also mounted on the mag. Accuracy is not bad and POI is right on.



There are also 4mm M20 conversions but the ammo is more expensive than centerfire. This one is a simple insert for 9mm pistols.


I also have a couple of conversions for shotguns and a 12gauge to .38 Special has POI spot on and is accurate but for the price of it, it also should be.



Does anybody else enjoy conversions as an understudy to a centerfire pistol?

[jetinteriorguy]

One thing I don’t quite get with the revolver conversion, how do you ding the rim with the firing pin when it’s designed to hit in the middle?

[JimCunn]

I also like caliber conversions.
My Uberti 1860 Army .45 acp Conversion.
Oops. Can't upload photo.

[Jim Watson]

I had a Colt Conversion, replaced with an ACE and a Nelson conversion, far superior in accuracy and reliability. Only point of the ACE is that the floating chamber gives a bit of recoil.

I have an AR .22 LR conversion; the .222" lead bullet in a .224" fast twist barrel ain't much. I have heard of rimfire uppers being built around the conversion bolt but with correct barrel.


I think I know what is going on in that revolver conversion but will wait for Pz to explain.

[PzGren]

A photo says more than a thousand words.



I also have a CMMG conversion for the AR. Accuracy is about tennis ball size at 25 yards. Making it minute of family sized pizza at 100.

[PzGren]

Here is a photo of the P1 conversion. The BMI stamp and army proof marks are visible, as is the ejector.



This is a comparison of a standard P1 slide and the .22 slide. The .22 is not cut for the locking block.

[44 AMP]

For me, the best caliber conversion pistol is the Contender. Take off what ever centerfire barrel you're using, put on the rimfire barrel, flip the firing pin to rimfire and you're done.

Also since the sights are on the barrel, there is never any change in POI, vs POA once you have it sighted in.

[jetinteriorguy]

Originally Posted by PzGren

A photo says more than a thousand words.



I also have a CMMG conversion for the AR. Accuracy is about tennis ball size at 25 yards. Making it minute of family sized pizza at 100.

Ah thanks, the picture posted in the first post sort of threw me. I thought the brass part in the cylinder adapter was the base of the .22 case and was dinged in the middle, but it’s just the part that is struck by the firing pin actuating the striker for the rim of the case.

[ballardw]

Does the Rock Island 22TCM / 9MM count as a conversion when they are shipped as such from the factory?

[DaleA]

I have a Colt conversion unit with the floating chamber that is only marginally accurate and the floating chamber gets very dirty, even with copper plated ammo.

I encountered similar problems.

With lead nose .22LR the floating chamber jams completely with less than a box (50 rounds) fired. Strangely, even with the floating chamber completely jammed up the gun still fired and cycled normally. I believe The American Rifleman had an article about beveling the floating chamber so it doesn't shave lead and jam up. I took my conversion unit to a smith who said they took a very little amount of metal off and told me to bring it back and they would bevel it more if it still had the problem. It still had/has the problem but I got a Ruger Mark II and never took the conversion unit back.

Also strange was the best accuracy I got was with Remington standard velocity even though IIRC the manual said use high powered .22LR(i.e. regular .22LR, not Stingers or other super high powered rounds.) (Note: My memory might be wrong about what the manual said though.)

[alistair]

Someone gave me one of these; converts 12gauge shotgun to shoot .22

https://www.gunadapters.com/12-gauge...venger-series/

[44 AMP]

Others might define it differently, but to me a caliber conversion replaces part(s) of the gun, with other parts to fire the new caliber.

Parts that are inserted into the unaltered gun I consider to be "adaptors". Very common for shotguns (once upon a time) also works with other guns, where a chamber adaptor takes the place of the normal cartridge, allowing the firing of a sub caliber round.