I copy you 100% on UTG as it equates to the powder burner uses. But I have to say, I LIKE there rings!!
The XS-25 has a scope stop to prevent walking.I was a bit confused when I first opened this post. I read that you were looking for upgrades to a Mike Mellick fully tuned XS-25. I thought to myself..."how could one improve on a MM tune". Then I realized you were talking about a scope .... LOLWe bought 2 of MM full tuned XS-25 and love them. He detuned Betty Lou's for easier cocking effort and did a perfect job. I actually opened mine and chopped about 3 coils off of my spring as well. Not near as easy as hers though. We haven't done any chrony testing but I start a 12 day holiday break on Wednesday and plan to catch up on all my projects.
make sure you tighten the mount very well. mine sheared the stop right of. also, i don't think that williams sight will fit the curved dovetail of the 25
Sorry, I made my post thinking the XS 25 was a clone of the Diana 34. The 34 has no hole for a scope stop pin. Set up your mount and torque to factory specs. You should be fine.