Early ‘80s, ours had metal poured down the barrel and the bolts welded shut.
This was in Washington DC public HS, up unil 1965 when I graduated.
At the start of the school year we were issued our rifles with sn numbers recorded.
We were taught to field strip them, but for the trigger group. During the week, using our free period or before/after classes, we were expected to clean them for weekly inspection. We were responsible for them after checking them out from the armory.
Only once was a rifle missing from the armory after pre-school drill. Before first period class, school was locked down. The Army Major advisor and our student commanding officers went straight to the students locker where they found it. Dofus had been dicking around late for class and rather than returning it to the armory. Next day in the stadium, the Major, using salty language for that era, introduced the offenders platoon to “high port” running drill, 3x around the track. Lesson learned by all.