[acrosome]

Originally Posted by Icelander

Bulk -5* if I can find a plausible way to combine a folding stock with good shooting at over half a mile), so the barrel can be up to 22" or so if necessary.

Ugh. I know of AR15's with alternate recoil systems that allow foldable stocks (the SIG-Sauer MCX comes to mind but there are others) but not AR10s. Let me look around. FALs have a reputation for poor accuracy, but maybe some HK rifle? Gunsmithing either of those is somewhat more complicated than an AR, though.

Oh, the SCAR-H has a folding stock, and the US military is adopting a marksman version. (And there is even talk of adopting a 6.5mm caliber...) Would that work for you? The US special ops community seem to have decided that he SCAR-L isn't all it was cracked up to be (some sort of issue with short-stroking in certain situations) but they still like the SCAR-H.

And there is this thing.

Originally Posted by Icelander

I'm currently studying all sorts of ballistics reports looking to see if I can find a round that will perform well at up to 1,000 yards from a 14.5" barrel. That would be for a Bulk -4 'do anything' super-carbine. What's really crucial is that it retains velocity well enough not to enter the transonic range until after the 1,000 yard point.

I don't want to go all negative on you, but... that's a tall order. :)

Originally Posted by Icelander

What really surprised me when I started looking into the issue is that overall length often limits the use of the longer, heavier, more aerodynamic bullets available in a given caliber in semi-automatic, magazine-fed rifles.

So, yeah, there are .308 Winchester and .30-06 handloads with very good ballistics and many semi-automatic battle rifles exist in these calibers, but if you load the 190-220 grain bullets that allow for high SD and BC and good long-range performance, you can't feed them from magazines or chamber them reliably in anything but what is effectively a new design of a semi-automatic, one bearing only a superficial similarity to the original weapon.*

This makes various rounds in 6-6.5 designed for modern propellants and long, low-drag bullets attractive.

You're preaching to the choir, Brother. I'm a 6.5mm fanboi. My .260 is like shooting a laser.

Originally Posted by Icelander

I'm really looking for a 'super-5.56mm carbine', something designed for optimal long range performance from a 14.5-inch barrel AR-15 platform.

Originally Posted by Icelander

I'm trying to find some good cartridges for accuracy and nice ballistic qualities at very long range which aren't all that much larger than .308 Winchester, or, at the very least, have been proven to work reliably in some design of double-stacked magazines that could be copied by a qualified gunsmith character (Armoury at skill 14+, as noted several will have skill 16-18).

Also a tall order. That's sort of contrary to the whole point of a short 14.5-inch barrel, and the people who have designed rounds for them (e.g. 6.8mm SPC) definitely had different goals. I really can't think of a round with that design goal. Even .224 Valkyrie was made for longer barrels. I think the closest you can get (or at least the best I can think of off the top of my head) is an AR10 or SCAR-H in some 6.5mm caliber. And since a fair number of the special people are carrying 7.62mm rifles nowadays I don't think that's much of a stretch.

If you want the accuracy at those ranges, you're simply going to need a long range rifle.