.22 LR & .22 Mag. Chamber Pressures & Revolver Conversions


May 15, 2008, 05:51 PM
Hello Folks,

I haven't posted in a while, but have a question.

I've been studying chamber pressures for like-caliber rounds and have found the following to be the case:
1. Chamber pressures for the .32 S&W Long are the same for the .32 H&R Mag.
2. Chamber pressures appear to be the same (24,000psi) for the .22 LR and the .22 Mag.

This brings up my question:
Since revolver cylinders in .32 S&W Long can be safely rechambered for .32 H&R Mag., in good quality revolvers, can this not also be safely done in revolver cylinders chambered for .22 rimfire- rechambering to .22 mag.?

Now I know that the .22 rimfire has a .223 bore, while the .22 mag. has a
.224 bore, but for short barreled revolvers, this should not be a problem.

My concern is the cylinders handling the .22 mag. loads. Should they not handle the magnum rounds if the chamber pressures are about the same, particularly in well made guns?

Your informed thoughts are much appreciated.


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May 15, 2008, 06:15 PM
Chamber pressure of the .32 S&W Long and the .32 H&R Mag are not the same.
The former is 15,000 PSI, and the latter is 21,000 CUP.

Second, you are quite correct that the RF pressures are pretty close.

But not if you try to squeeze a Jacketed .22 Mag bullet through a .22 LR barrel designed for lead bullets. Pressure would increase quickly.

The weakest link in the chain is the Magnum rimfire case itself, not the gun. If anything bad were to happen it would be a blown case rim, not a blown up cylinder.

Also, a .22 RF barrel would have the wrong rifling twist and bullet tumbling would be a possibility.

In all, it's probably not a good idea.


May 17, 2008, 10:57 PM
Depends on if it's something that's designed and built to be convertible - there's an awful lot of different .22 LR/.22 mag single-action pistols out there, one of which I own. (FIE Texas Ranger, also sold under a number of different names and apparently now known as the Heritage Arms Rough Rider.)(My mag cylinder is actually off a Quality Firearms Western Ranger, and looks bloody nice.)

I'd suspect a dedicated .22 LR revolver would exhibit much more overpressure in this case, but IANAGunsmith.

May 18, 2008, 11:30 AM
.22/.22 Mag convertible guns have .22 Mag bore diameter & rifling.

That is why they are most generally more accurate with the .22 Mag then with the .22 LR cylinder in place.


May 21, 2008, 05:03 PM
I have seen several Ruger Bearcats with one chamber drilled to .22 mag. They claimed that they worked okay. Perhaps Ruger uses the same size bore for both or splits the difference.

May 21, 2008, 05:33 PM
Nothing personal, but that's about the dumbest thing I ever heard of anyone doing to a gun.

Must be someone local doing it.

Bubba's Bar & Bearcat Boring perhaps?

Even Ruger quickly gave up on the steel-frame .22 Mag Bearcats some years ago after a short production period because of problems.


Jim K
May 22, 2008, 03:17 PM
The main problem with converting any .22 LR gun to .22 Magnum is not pressures (except maybe for some real junk guns) or the barrel bore size. The real problem is that .22 LR barrels were almost universally made from soft steel, which works fine with lead bullets. But the hotter burning powder, higher velocity, and jacketed bullets of the .22 WMR will wreck a .22 LR barrel pretty quickly.


May 24, 2008, 12:36 PM
I suspect most pistols would be made from tougher steel. Many revolvers could be had in iether lr or mag. Just check the cylinder length. As for pressure with the smaller bore and jacketed bullet - surely by the time the bullet has jumped the gap and the forcing cone, pressure would no longer be a consideration? I have heard of quite a few folk who have converted lr rifles into mag. Case failure didn't seem to come up. Just my thoughts.

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