I was recently at my partners Auntie and Uncles place and her Uncle offered to show me his antique guns he had on display. He had an old musket of some sort and a Martini action Enfield, both of which had the barrels welded up to could never be shot again. He then took me out to his garage where he had a deactivated Bren gun, which was a lot of fun to play with. He told me that it was deactivated so couldn't be used, but the action and trigger and everything worked fine. I assume that all it was missing was a firing pin, but it seems a bit dangerous only having the firing pin missing to prevent it from shooting. Is removing the firing pin all that you have to do to deactivate a firearm?