Conversation so far:
when was the 30 round m16 magazine introduced
Production of the 30 round magazine for the M16 started late 1967 but did not fully replace the 20 round magazine until the mid 1970s.
how much do standard usgi aluminum 30 round m16 magazines weigh
Standard USGI aluminum 30 round M16 magazines weigh 0.24 lb empty

Question: how long are the magazines
Self-contained rewrite: how long are the 30 round m16 magazines