Bartholomew Roberts : Yes; but in a package that is at least 5" shorter (assuming a folder AK). Remember you are comparing full-size AK performance to SBR .308 performance. If I take 5" off an AK barrel, the already rainbow like trajectory of the 7.62x39 is not going to improve. On the other hand, the 7.62x51 will still be effective at 300m. The AR can hit just fine at 300m with the short barrel; but it loses a lot of effectiveness with the loss of velocity and you'll never get it as compact as a folder SBR because of the buffer tube.
The reason we have different outlooks is because you are only considering the ballistic performance. I am considering the ballistic performance for its size.
I'm considering its ballistic potential for its size, it's just that an AKM with a folding stock is pretty damn short even if its barrel is a little bit longer that what your SBR's barrel would be (11 inches vs. 16 right?). The main purpose for an SBR is to clear rooms without your barrel leading you through the doorway and its ease of getting in and out of cramped vehicles without it smacking into anything on its way out or into the vehicle isn't it?
I realize what it's for and I understand the fact that you'd be getting a powerful carbine in a really short and handy package, I guess that the AK folding stock is just short enough for me without spending an extra $1000 or so just for the weapon alone, without even going into the added expense of .308/7.62X51 ammo right now. I can't even afford to shoot my .308's right now due to the prices of ammo going up. Perhaps you're better off financially than I am though, I'm just a lowly EMT and $450 for a 1000 rds (.308) vs. $158 for a 1000 rds (7.62X39) makes a big difference to me.
I'd probaly get an .308 SBR myself if you could just get them off the shelf by filling out a regular 4473 the way you would with a regular firearm and if it didn't cost so much.
To me it just isn't worth it merely because of the paperwork and legal hassles of getting a NFA weapon and the extra money that it would cost, not because it's a bad idea on the basis of what it's for or because of its use potential. To me it doesn't really do anything that a $450 AK couldn't do in just a slightly larger package, but mostly it's just about the money and the hassle for me.
I just guess that I don't have that much trouble being able to do either of those things with an AK if I needed to. Those Krink AK's do okay even though the barrels just as short (I've fired some of the AK "pistols" using a sling to steady it by pushing forward although I personally don't own one myself), especially for engagement distances that are usually across the street. If I remember right projectiles from a 7.62X39 are going about 2100 FPS from a Krink. Perhaps I'm wrong, but talk of good groups with a carbine that's got an 11 inch barrel at 300 yards seems somewhat optimistic to me. Then again I don't have much experience with short barreled firearms with a stock as that's what I can get without a tax stamp and without too much hassle.
An SBR seems like it would be basically for across the street and across the room distances and you'd have it in .308 for a little more thump and penetration through building materials and vehicles, I just can't actually see it making very good groups at a couple hundred yards.