That's OK John.all done now and all went well.what made it easier i clamped gun in vice with wooden off cuts and towel to protect stock from damage,made it so much easier.I countersunk pilot hole and first tried an old type hand drill without much luck and then successfully used a small lithion screwdriver with drill bit and built up size of pilot hole starting with 2mm.Threadlocked the swivel,screwed it in as much with hand and finished off by placing small file into swivel and slowly turning until home.so jobs a good one,alls left to do is zero her in.