I had the same problem with my finnfire varmint, it's basically the same action, the problem started with cci subs and not being able to close the bolt, after emailing the cci manufacturer their reply was the finnfire has a tight match chamber and the lead and wax build up caused the problem, also because of the match chamber (low free bore,the area ahead of the bullet ogive in a rifle barrel to which there is no rifling) high velocity rimfire ammo should not be used, ie Stingers.
Winchester subs are inconsistant in the quantity of wax they have on them, mostly too much, occasionally leading