I tightened it very tight with a good, wide-bitted screwdriver, but it has loosiened on me two or three times now at the range where it is fired about 30-35 times. I will admit that the.416 Taylor rounds are putting the action to the heavy test, even though I am getting no pressure signs on my easily extracted cases. The latest is that the bolt head retainer pin broke in half which I will easily replace. Thanks for all the suggestions. I'm sure they will solve the problem with the bolt assembly screw.