That sounds good, but uh....A 12 ga shotgun loaded with 3" #4 Buckshot will send 42 .243 projectiles each time you pull the trigger. With 5 rounds, that is 210 projectiles!
An AR15 will send ONE .223 round each time you pull the trigger. With a 30 round mag., that is 30 projectiles.
To each his own. If you want a shotgun with five rounds of buckshot, go for it. I tend to believe more rounds keeps me in the fight longer. So have at it with your five shots. Chances are that may be all you need. I'll take my chances with four 30 round mags of .223 and 51 rounds of 9MM.