Thanks everyone. I've taken MANY Marks apart but this one is giving me a hard time. I'll try the freezer trick followed with Kroil. Wish me luck. I've only had to send one back to Ruger but that was a stainless Mark with a jammed mainspring assembly because of a slipped pin.
I've had to employ the plastic mallet thing a few times with a new and really tight Mark II. They wear in a bit after a while.
I have one I bought used that has gotten quite loose. The mainspring housing pin is what really holds it together.
Remove the housing and it darn near falls apart. Still shoots great.
Try a hard rap with the plastic, or wood, mallet before you send it out for a repair it likely doesn't need.
Be aware that you will probably have to drive it back on to the frame again if it is that tight.
Well again! After it warmed back up to room temperature I thought why not give it one more shot. So I got out my dead blow mallet and gave it a whack. The barrel started moving and came right off after a few hits. Only thing I can think of is that the freezing and thawing freed up whatever was hanging up and let loose. ???????
Perhaps the frame warmed up faster than the barrel/receiver, which meant that the frame was just a tiny bit larger and allowed the slightly smaller barrel/receiver to part company. Saved a trip to the barn, anyway, eh?
It had sat overnight so everything should have been the same temperature. Up side is that I finally got to give it a good cleaning. I did have to use force to get everything aligned on reassembly so there is still an issue. I agree about the barn. As nice as the folks at Ruger have been to me (for the most part), I was glad that I didn't have to send it in.
Reminds me I of a gun I had years ago. Semi custom and I had the manufacturer do a trigger job. It was sweet. Come fall I'm at a match and it won't stay cocked. I played with it a bunch, no go. Next day I test it and it worked fine. Go out and try to shoot it and it started acting up again. Had an idea and tested my theory. When the gun got cold it lost engagement. I sent it back to have it checked and the smith told me it was fine. I told him to put it the fridge overnight and try it. He was absolutely amazed.