You can actually do it on all vendors (i’v tested it) it just depends on which ammo type, if the vendor has multiple ammo types and the first one doesn’t work - then try the second, took me awhile to figure out why it wasn’t working :) Also if you do not have that ammo type in your inventory it will not work > it…

Haha, same thing happened to me, except i wasn’t killed by the raider, i killed myself with a fatman i found doing one of the main story missions. I was like “oh, i think i’m gonna fire this indoors” >sudden death & achievement pop