Just to add something a little different, I have recently fitted a "barrel weight" to customers F Class gun that he was having trouble getting it shoot consistently (shoot well one day and terrible the next), so we glued on a 600 gram weight on the end of the barrel (flush with the end, not overhanging and not adjustable), well it turned it from very fussy to a rifle with a huge tune window.
Regards
Matt P
Regards
Matt P