" to help clean the insides of the bolt carrier and star chamber"
in those 2 applications, it wont hurt anything.... just dont use it in the barrel at all...
that said, the star chamber should be cleanable with break cleaner and no brush...
if the other person has no access to the gun IE: its locked up and they dont have a key, then the courts have ruled that is kosher...
but if not secured, then they "do" have access...
as for a "buddy"... no different then a "buddy" walking into a gun shop or gun show or a shooting range...
British sniper in Afghanistan kills six Taliban with one bullet - Telegraph
The 20-year-old marksman, a Lance Corporal in the Coldstream Guards, hit his target from 930 yards (850 metres) away, killing the suicide bomber and five others around him caught in the blast. :p
338 AI
EDIT"...
i use JB on a patch, wrapped around a 410 shotgun swab chucked into a cordless drill... i also do then when i have a die that starts scratch the brass from a build up of small brass "chips" that embed in the die...
ive used 748 for 223 since i started loading in 1994... great powder... kinda slow on the heavy bullets, but will still shoot well.
works best for speeds in the 40-60gr loads