Hi Rayg, Whether this helps a trials rifle I don't know but here goes.
You probably know my no1mk6 screw is no longer the same thread and the usual cut off screw won't do the job, but my solution thats works fine was to take the threads off with a dremel/file and just push the screw in the hole. To make it sit deeper than flush, which it needs to keep the far end of the screw in its bush/hole end I put a little ball of paper on the screw head and let the fore end close up on it. To get it back out it either falls out, or a magnet draws it out, with the cut off open so there's little tension on the screw. It even saves the original thread in the rifle for the future insertion of the correct unit.

Thanks to all for the suggestions about the trials cut off, I've been under the weather for a bit, so now I'm back to making a decision.