to control headspace, you ABSOLUTELY NEED the cross pin!!! do NOT use set screws! this is a critical safety feature that, if screwed up, can cause serious injury or death.

as far as a fit goes, yours sounds loose. the commies use .003" to .006" INTERFERANCE fits, thus mandating the use of some sort of press or heat/cold fitting.

this is not to say that you have a setup that is too loose. did you bbl. and trunnion come from a matched kit/rifle that was once assembled to each other? i have heard of guys that turned their bbl. journal down too far and had a slip fit in the trunnion and their rifles are holding up...but i would procede very carefully at this point.

although the cross pin controls the majority of forces that affects headspace, the fit in the trunnion helps control front-to-rear bbl. movement AND accuracy by controlling the side-to-side and up-and-down movement as the rifle goes thru temperature cycling.

trust me. as a design engineer with over 23 years of on the job expirience, i can tell you that a thread form will not locate nearly as accurately as a dowel pin.

using a thread form as a locator for controlling the headspace is dangerous. stick with the dowel provided by the factory.

those tight press fits that require a great deal of force to fit the parts together are for a very good reason...they accurately and repeatably control the location of those critcal dimensions. headspace is a very critical location. ±.005" can mean the duifference between a safe firearm and one that is a disaster waiting to happen.