Jim Tayor, your father's 22 SA with the one 22M

I now Ruger over the years has issues a couple of differing bore sizes to help the issue. In my experience a tigher hole taking an oversized slug fared ok. It's the opposite that gives me issues. Or a tight cylinder that squeezes the bullet down a couple thousandths before it even gets to the barrel to rattle down a lose bore.

The little Colts are pretty but not well known for accuracy compared to some. I'd love to hear from those with more experience. I think Woody has at least one.

Plus rimfires can simply be finicky with ammo. You might expand your testing and try others, take notes! The Armscore 22 WMR is really good and I like Winchester too.

a 22 magnum bullet that is the culprit. The 22 LR bore size (If I remember right) is .218 to .219 whereas the 22 magnum bore size is in the .222 to .224 range. It doesn't sound like much but in a lot of cases where you have 2 cylinders of different calibers (22 LR is .222 bullet and the 22 Magnum bullet is .224) one cylinder will often shoot much better than the other and it is not unusual for one to keyhole a bit.
There could be another issue there, rough mouths on the cylinder, oversize cylinder mouth or way undersize, etc. Without seeing the gun I couldn't do more than guess, but in my humble experience Colt barrel bores have been a bit tight for caliber and that could be your problem. If I had the gun I would clean it up good and put it on gunbroker and sell it for a good price. That gun should be in a collector's stash. Then pick up a good Ruger Single Six. Just a thought.

If you have Gary put a linger throat in it like his big bore ones, it will usually clean it up. Oversize bullets work best that way. I am in the Republc of California right now and can't write too mich.