That's the minimum. Depending on how the upper is set up, you could need new handguards or rails.
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I'm sorta "that guy", in that I've never shot or handled a middie.. but I knew I wanted to pickup a 2nd AR, and I knew I wanted something very different than the 6940 I bought as my first AR.
All of my buddies already had middies, so I decided to jump on the train. While jumping on the middy train though, I tried to do it right this (or atleast better). 14.5" barrel (I've read the 14.5" barrel will do anything a 16" would), LW profile (lighter & supposedly better balance vs. Gov). 12" RIS-II rail (can get my support hand much further out than the short rail on my 6940). Final mods will be a GF charging handle & pinned Battle Comp.
Im still waiting on the build from Smartgunner, should be here in about a month or so. But Im expecting it to look, handle, shoot, recoil and even sound much differently than my stock 6940. Im pretty excited to see the difference and think it makes for a great 2nd rifle! Might even SBR the lower.
You mentioned that your Carbine has a MOE handguard, which IMO weighs almost nothing. It is nearly all plastic and short (approx. 7 inches). On the other hand you have a middy with a VTAC extreme (probably 11 inches) and made of aluminum. So there is a huge wieght difference there. Spend a few bucks on the MOE middy and see if that makes a difference. But I am not sure as to how much effort it would be to do that swap.
But I think it is not the gas system that is causing the muzzle heaviness. It is likely the different handguards.
My personal opinion is 14.5" and less barrels are carbine length, 16" are midlength and 20" are rifle.
My 6920 has a genuine Colt M4 barrel and a pinned Blackout on it, my 16" midlength is a BCM BFH lightweight and my rifles are all retro 20" barrel 603 and 604 clones, plus an SP1. :D
From your poll thread it's the giant flashlight you have mounted on it (with no comparable light on the carbine). If both rifles had that light on them, they'd be equal (or with a nod towards the middy). My 16" LW middy is handier than my wife's 6920 (16" carbine) because of the barrel profile and the fact that I grip it further on the barrel.
I'll admit I was that guy. I just got it last spring so I wasn't quite keepin up with the jones'. I needed (subjective) a second and picked up the middy to see what it was all about. With the LW profile and just a DD rear sight it's nice and light. Most likely that's why I don't notice it shooting any softer. Just a phantom on the end of it for now. It will be my training gun this year. It'll get a small light and probably an H1, maybe a Sparc depending on Vortex's warranty, and that's it.