Glocks that have the non-rifled bores can fire lead bullets.
Lead gets left behind.
All normal so far.
But, at any moment,
with no warning, the deposited lead can grow, reducing bore size.
The following bullet may not like that
Some lead-shooters
clean the bore on a rigorous and short rd-ct schedule; safe!
Some don't; not safe.
And some (all too often) learn the hard way......