I have a Colt LE6920 I purchased about a year ago, of course with the carbine length gas system. I thought I had the last AR I’d ever need, but reading about these midlength gas systems has started to make me doubt. If I really want a top of the line AR, should I have gone with midlength? Now I’m considering getting a BCM middie upper, but then I’d be tempted to just get a whole new middie rifle and leave the Colt as is. And THEN I started lookin at Mk12 uppers with 18” barrels and rifle length gas systems, which should be even more reliable and durable than the midlength. However, perhaps an 18” barrel isn’t optimal for home defense/general use, which is what my main “go to” AR is slated for. I do like the idea of a Mk12 upper though. There’s actual data by the military showing the advantages of rifle length gas over carbine, unlike middie. Are the advantages of the mid length enough to get a new midlength carbine/upper? Or would I be better off spending the money on ammo and practicing with the Colt? It’s never had any problems, but I’m going to a 1,500 round carbine class soon.