Not counting .22s, I bought my first semi-auto rifle, an M1 carbine, from DCM back in 1963 just for the fun of it. I was a brand new 2LT and did it all by mail just because I could.
I never felt the need of another until Bill Clinton because I do most of my rifle hunting with a Ruger No.1. But no one was going to tell me what to use, so I bought a Browning BAR in 30/06 as a hedge against Bill Clinton's designs. The Browning is a nice rifle, but I still use the Ruger to hunt with. Since then I have added M1 Garands and M1 carbines for the fun of it for competition at the club and to play around with in my retirement.
Then, after years of saying I would never buy an AR15 because of an horrible experience with one in Vietnam, I bought a Rock River AR15 -- M4gery -- at Camp Perry to use in club matches because shooting an M1 Garand left handed in rapid fire is close to impossible. I liked the new AR and bought a Fulton Armory varmint rifle with a fixed stock and floating hand guard last year at Camp Perry to use out West on a prairie dog hunt and to replace the M4gery for club competition. But I really bought the Fulton Armory one because I was sure at the time that Hillary was going to win and try to take all the ARs away and so far I have two grandsons. If any of my granddaughters show an interest in shooting, as their mother did I will add some for them too.
Just for the record, after trying several real assault rifles in combat I found that the M2 Carbine was the best for me. It was a good weapon for an officer or NCO at platoon or company level at the time. I don't claim to know what is best for today's LTs.