I've got a 1896 Swedish Mauser that I had rebarrelled a while back.  If I let it get completely cool between shots, it groups great.  "Completely cool" means "let it set 20 minutes between shots."  If I don't, it strings vertically.  Some barrel preload fixes that, but I'd really rather leave it free-floated.  Barrel preload is tough to maintain consistently, and if you don't, the zero wanders.

At this point I'm willing to try cryogenically treating the barreled action to see if that will stabilize it.

Anybody had this done?  Did it improve things?  Did it have any effect at all?

... Yes, only because of anecdotal evidence and the bargain afforded me. It's a sub-MOA M700 but I have no idea whether or nor the cryogenic treatment contributed to it.

... The thesis on it sounds convincing.

I had a Ruger 77 .30-06 that would do vertical strings until the barrel was warmed up. Had Vollmers cryo freeze it and it would shoot the same point of aim from cold to hot after that. I don't think it is the be all trick, but it did help that rifle. If you do do it, be sure that you remove ALL springs as the freezing process will ruin them.

My CMP "Danish" Garand has a very nice Danish barrel. The problem was that it was all over the paper.  I couldn't call a shot. Bushel basket sized groups.

I bought three books on how to accurize it but nothing worked. I even put the 4 jaw chuck on the lathe and re-crowned.  No effect.

I sent the barreled action in for cyro treatment. It was back in a week and I reassembled it.  Now, if I am out of the X- Ring, it is my own fault.  

For carefully prepared target barrels, there may not be any noticible change.  In my case the cyro helped a lot.

Thanks.  I think I'm gonna do it.