That looks like a good idea except for the barrel length. The .22 magnum is notorious for requiring a long barrel for anything like normal performance.
Out of a 4 inch it would be hardly better than a .2LR. I would have a tremendous muzzle blast tho.
I have .22WMR in a 6.5” Ruger revolver. You can definitely tell the difference from 22LR at that length.