Barrel.......... some do, some don't. Crap happens.
or had/has residue builup.
you would be amazed....
Try gettin a rifle barrel cleaned enough to shoot barnes bullets.
once ya do, yes, they will shoot very well indeed.
just an opinion....
and, so far... my glocks seem to shoot okay with the lead bullets I have tried. I do however keep a good eye on it.
hope that helps.