View Full Version : converting 22lr chamber to 22WMR?

September 1, 2010, 01:16 PM
i have a crickett single-shot 22 rifle, with a 1" stainless bull barrel.

i was wondering if the bore for a 22lr is the same diameter as a 22wmr?

would be a handy little backpacking rifle if i could have the chamber opened up to accept 22wmr ammo.

i suppose the bolt face and extractor would have to be compatible too.

any resources for the dimensions of these rounds?

Jim Watson
September 1, 2010, 01:46 PM
The bore is NOT the same.
.22 lr is around .222" groove diameter if not a bit under.
.22 WMR is .224", same as most .22 centerfires.

Is the Cricket strong enough to stand swaging the bullet down? I dunno.

The rim diameter of .22 WRM is larger than .22 lr. Will that mean the firing pin would not hit near enough the edge of the rim for reliable ignition. I dunno, but you should before you start cutting steel.

September 1, 2010, 01:57 PM
In addition to the bore and cartridge dimension issues Jim mentioned, most 22 LR rifles have very poor lockup. Since the 22 WMR operates at much higher pressures than 22 LR, you may run into bolt jamming, extraction difficulties, and possibly rupture a case in firing. FWIW, I have seen very few 22 LR to 22 WMR conversions over the years that worked well, most had one or more of the issues mentioned.

September 1, 2010, 02:04 PM
well, upon looking at the crickett website, they now offer them in 22wmr and 17hmr..

may not be worth the trouble if i can just buy one.

thanks guys, nevertheless

James K
September 1, 2010, 08:13 PM
I don't know about that little Cricket, but most barrels for .22 LR are made of fairly soft steel, while those made for .22 WMR are hardened to stand up to the greater heat, higher velocity, and the jacketed bullet. A .22 LR barrel won't last long firing .22 WMR. That is the main reason why WMR guns cost more than the apparently same gun in .22 LR. And why rechambering a .22 LR to .22 WMR is not advisable.


December 9, 2012, 06:52 AM
This old thread is still often a topic of confusion with theories often more common than real facts. This conversion has been done thousands of times and with a break action gun like my model 24,nothing had to be changed. Even the extractor worked fine with just a little emery paper work. The big concern of most people is the much higher operating pressure of the .22 Mag but it isn't higher. Max pressure levels of both .22LR and .22 Mag are exactly the same at 24000 PSI. Surprised me the heck out of me too. The difference in Rim Dia shouldn't have any effect on misfires.
There is a bore diameter difference of .002" but a bullet swages down in tight bores by the time it travels once its own length. Some have reported less accuracy after the conversion but most don't notice any difference. If the gun isn't accurate to start with, don't expect much improvement after the conversion. The pressure increase due to the smaller bore would much less than expected. 6.72x39 ammo has a .311 bullet but are safe to fire in American made guns with .308 bores. The Ruger Mini 30 is just one example where Ruger has stated it is safe to fire military surplus ammo for the SKS and AK 47 with .311 bullets in the Mini 30 with a .308 bore. I converted my ".22LR over 20Ga model 24" because I often hunted rabbits in open fields including big jacks that would often bolt from too far away for the 20 Ga but frequently would stop running around 100 to 150 yds away and then stand up to look for the danger. Too far for the .22 RF but within reach of the .22 mag with a slight hold over at the longer ranges. The .22 mag is much better for the numerous Coyotes here as well. .22 mag is too expensive for my plinking habits or extended target shooting but inexpensive for hunting and with more than 2X the range and energy of a .22 LR. I wouldn't bother converting a bolt, pump or lever gun. The much longer .22 mag case makes that a very complicated issue. Not a problem with a single shot break action.

December 9, 2012, 11:04 AM
how much does it cost to convert a 22 to 22 mag? i have bought two 22 mag rifles, both were under $200 each with great accuracy allowing me to keep my 22's intact. i have a marlin glenfield model 25 in 22 cal that i bought new in 1969 for $29 that still shoots moa at 100 yards. why would i sacrifice that?

James K
December 10, 2012, 09:07 PM
Maybe there is no problem with single shots, but I suggest not converting old Flobert rifles to .22 WMR.


December 11, 2012, 06:04 PM
This old thread is still often a topic of confusion

Must not be too common an object of confusion if you had to drag up a two year old zombie thread to comment on it.