Carbine gas vs mid-length gas...

I did search for this info, but I couldn't find any authoritative discussions...

I don't want to pay the tax for an SBR, and I don't want anything permanently attached to the barrel, so I'm only considering 16" barrels. Given that, which is better and why? I remember reading that the mid-length may absorb a little more recoil, making it a bit more manageable - is that true? If I had two uppers, one mid-length and one carbine length, that I used on the same lower (don't ask why - this is a theoretical question to help me understand the differences), would I need a different buffer for each upper?

I have a hundred questions that all get at the same goal - please help me to understand the difference so that I may choose the one that will be most reliable & will work best for my needs.

Thanks!

If going 16" and you have the choice, midlength is THE way.

https://www.m4carbine.net/showthread.php?t=7009

I own both (Colt 6920 & a colt lower/SDI recce upper that I got from talon arms) and enjoy the milder recoil of the 16 inch middy. The recce build has a Magpul SPR stock which allows me to use a A2 buffer, so that, with the mid-length, practicing precision slow fire, makes it an all day, very mild shooter. Both are configured for different reasons and use. Once I'm settled in, I don't mind the recoil of the 6920 either as it is not a mule kicker. The recoil doesn't bother me until after shooting 500 rnds or more in a few hours time or during a class and not until the next morning (Gotta work on those push-ups!). On the 6920, the rubber padded LMT stock helps quite a bit and so does the H buffer. They do have rubber pads to ease the recoil on a standard stock. I bought it last year because I joined this forum and wanted one for my birthday, before the prices went through the roof.

As far as using different uppers on the same lower, sounds good to me, just run with an H, H2 or a 9mm buffer (IIRC), it's close to the weight of an A2 buffer, slows down the cyclic rate and dampens perceived recoil, so you'll have the best of both worlds. I like both for different reasons, but if I had to keep one, I'd keep the Middy!;)