It is, but the mag cartridge fits the cyl window easily. So a J frame cyl and adjusted bar/cyl gap is the solution.
The I frame cyl is not too short for 22WRF, however. Currently loaded again and offered by major ammo makers. Cheaper than 22 Mag and not as loud! Not a whole lot less power either.
And the best thing is, it's pressure is only 19,000, not 24,000 like 22 LR and Mag.
But stick to an I frame made after 1945, it will have the post war improved steel for the 22 mag. Plus the shorter cyl window of the I frame has a bit greater frame rigidity than the J frame with its 1/8" longer cyl window opening for LR and the Model 51 22 mag. Because the smaller rigidity ratio increases strength of the I frame w/smaller cyl opening, over the J frame w/longer cyl window.
The difference in bore and groove diameters of the 22 LR vs. 22 mag are negligible. Both are given as a range, and the top of the LR range can overlap with the bottom of the Mag range. Therefore not really an issue. If anyone is really worried about this, just lap the barrel a few thousands larger for 22 Mag.
Hope this helps,