Nice original rilfe. You might want to ensure you have the correct bolt head for the No4 MkI* that has the bevelled front and rear edges on the bolthead guide. It looks like you the unbevelled kind that was used on the standard No4 with bolt head release via the catch. The kind you appear to have is known to sometimes 'jump' up enough on opening or closing the bolt to hit the edges of the bolt head release slot and damage the edges of the bolt head guide.

I think I posted a closeup of that somewhere a while back.