Tactless remarks about black American's old musket (11)
I believe the answer is:
blunderbuss
'old musket' is the definition.
(I've seen this before)
'tactless remarks about black american's' is the wordplay.
'tactless remarks' becomes 'blunders' (blunder can mean a thoughtless remark).
'about' is an insertion indicator.
'black' becomes 'b' (as in pencil classifications).
'american' becomes 'us' (abbreviation for United States).
'b'+'us'='bus'
'blunders' placed around 'bus' is 'BLUNDERBUSS'.
(Other definitions for blunderbuss that I've seen before include "Early form of gun" , "Old musket" , "Weapon" , "Short large-bore musket with flared muzzle" , "one was fired" .)