I purchased a modern sporting rifle about 1976, and still being on good terms with the ROTC instructor in High School, he invited me to teach a class on it.
So, I walked into school thru one of the many open doors with my rifle in a black Assault Systems case, pulled out the HK91, and gave five classes on it. Gave the history, tore it down, passed it around, seniors and freshmen alike. No problems at all, a small southwestern Missouri town of about 40,000 then. Then, no open carry was allowed by municipal regulation, tho. Now, open loaded carry is legal and fairly common. Just avoid schools, churches, the post office, etc.
Things change. I sold the HK and later built an AR. Much better rifle, and shoots much cleaner, too.