I have a 527 varmint in .17 hornet. I think they are 1/2" thread. I had mine cut to 20" and re threaded 1/2" then re crowned by DM80. I also had a custom mod done for it by DM80, it is very quiet. I like the calibre a lot it is very flat shooting but can be a little wind affected. Basically i use mine for rabbits etc at night with night vision, with the bonus of if a fox appears it is more than capable of killing it. If i was you i would get Dave to make you a mod for it as his are calibre specific, very quiet, light weight and strippable for cleaning. Oh! and cheaper than other mods that don't work too well.