One way or the other, the differences are not huge. 16" carbines work just fine, it's just that the midlength system is slightly more gentle on the action.
If we're talking a 16" barrel, here's how it breaks down:
Midlength Pros:
More gentle cycling, which results in less wear and tear on the gun, which result sin increased lifespan and durability. Be advised, in order to see any sort of a difference, though, you need to be putting a LOT of rounds through the gun, probably more than most of us will ever put through our rifles.
Longer sight radius, which enhances practical accuracy with iron sights.
Longer rails for mounting doodads, if you go that route.
Ability to use a bayonet, if you get a FSB with bayo lug.
Aesthetics (subjective)
Midlength Cons:
Generally, more makers produce car-length uppers and parts, so selection of middy uppers, rifles and parts is smaller.
The midlength weighs slightly more, and the extra weight (and the constant weight of the FSB) is out towards the nose of the rifle. However, this difference is REALLY REALLY small, and should probably be treated more as theoretical than actual.
Cost: since the middy is a rarer bird, getting one set up the way you want it will probably cost a bit more than a comparable car-length rifle.
So, the upsides are really small, but the downsides are even smaller. If you're running a 16" barreled gun, there's not any real reason not to go with a midlength.
Mike
Sadly, I've only been out to shoot it once since putting it together around a Doublestar lower from Bud's. But I love it so far. I hope to get out next weekend to get the irons fine tuned. As someone else said, it is a tad barrel heavy, but it is not objectionable.
