Knifemaker, you are right. The .22 Mag has the same bore diameter as .22 centerfire barrels. The reamer pilot diameter is .218". Pilot diameter for .22lr is .216". I talked to several people after doing the first one, which I screwed up. The consensus is that .22 Mag chamberings in .22 lr bores are safe and frequently very accurate.
I have verified the safety, but not the accuracy. I fired (2) five shot strings late last week, doing barrel break-in, neither of which were very accurate. 1 moa to 1 1/4 moa at 100 yds. I still have 4 more types/brands of ammo to test, so am not discouraged yet. If the barrel doesn't shoot any of them well, I'll rechamber it to .22 K-Hornet and try again. I have a.216" pilot for it also.
I didn't follow up on the thread sooner because I haven't had a chance to shoot it. I plan to just take a couple of rifles to the range and give them a good test, including chronographing velocities. When I know more, I'll do a better job of updating.
7mmSendero, I've just started follow-up testing on a Marlin 917VS after doing some badly needed stock and trigger work on it. So far, it's not very promising either.
Tom