[Icelander]

Originally Posted by acrosome

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.

Well, for an AR-15 type rifle, you can always put a Law Tactical folding stock adapter on it. See manufacturer's page. They appear to work adequately enough.

You can actually mount them on AR-10 rifles as well. That may or may not work as well as mounting them on the AR-15 platform.

My main concern here is that even if adding such an adapter has little impact on accuracy at typical shooting ranges, precision rifles are usually engineered to avoid any possibility of give or loose tolerances. Pretty much any stock will be sufficient for minute-of-bad-guy at under 100 yards and any reasonably well-designed one will suffice for the same accuracy at up to 300 yards. But I haven't seen many precision rifles meant to shoot out to 1,000 yards or even further that don't have stocks designed expressly for that purpose, with zero possibility that the stock will move slightly around while the shooter is aiming.

Let's say that if I were to allow that a folding stock could coexist with the best possible GURPS Acc allowed at a given Bulk, I'd probably want it to be a very solidly engineered one. A $200-$260 piece of metal that is essentially a work-around for a rifle that isn't designed for a folding stock may qualify, but I'd want convincing that it was the absolute top of the line in mechanisms that allow weapons to be carried at one Bulk lower.

Of course, just having a master gunsmith build essentially the same doodad, but with much more care and precision, at a cost matching Fine or Very Fine (Accurate), i.e. $350 for a Fine version (allowing use with Fine (Accurate) rifles) and around $1,000 for a Very Fine one (ditto for Very Fine (Accurate), might be plausible enough.

Originally Posted by acrosome

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.

Oh, indeed.

Something based on this, but in 6.5 Creedmoor, might be the gold standard for a DMR for supersoldiers who still have access to governmentally supported Tier One special operations units level resources.

In other words, the secret black ops people from the (almost certainly*) still extant DoD supersoldier program, who oppose the Onyx Rain faction trying to contain the fallout from the failed Jade Serenity program from the 90s. The scarily competent, precision-gengineered modern supersoldiers who will one day be sent to kill the outmoded, unpredictably powered PCs, their friends, their allies and even their enemies.

*By every narrative law of both technothriller and superhero fiction.

Originally Posted by acrosome

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

Everything I've found strongly supports a 6.5mm bullet of 123-142 grains, fired from a casing that will feed in a weapon designed for the 7.62x51mm NATO with minimal changes as the optimal choice for a supersoldier designated marksman rifle, i.e. the Bulk -5 rifle with a barrel of 18"-22". There might be arguments in favour of a 6mm bullet in 103-115 grains fired from a similar casing, though.

I'm still trying to find the optimal chambering for the 'do everything' super carbine, i.e. Bulk -4 or -4*, with a barrel no longer than 14.5" (see later reply to Douglas Cole about the possibilities of a bullpup for that role for an alternate build, though).

Leading candidates for a load so far are: a) some variety of 5.56x45mm, using one of the more modern loads with a fairly high BC bullet of 73-77 grains; b) .224 Valkyrie; or c) a handload or even a wildcat cartridge firing a either a .224 caliber bullet in 73-100 grains or a 6mm bullet in 80-105 grains from a casing that will feed in an AR-15 platform carbine.

Originally Posted by acrosome

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

Originally Posted by acrosome

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.

Oh, I know it's a tall order.

To be clear, I'm not expecting to be able to match the ballistics of a 6.5 Creedmoor from a 22" barrel precision rifle with any kind of handy AR-15 type carbine. Rather, I'm designing two different types of weapons, for two different (albeit somewhat similar) tactical roles.[1]

First, I'm looking for a designated marksman rifle with no more than Bulk -5, with better performance at 900-1,000+ yards than the 7.62x51mm (flatter trajectory, less wind drift and a longer range until it goes transonic), semi-automatic or otherwise allowing RoF 2+, with a detachable magazine capacity of 10+ (the higher the better, but much more than 20-rd would probably impact Bulk). This can be a rifle with a barrel length of up to 22", or even a couple of inches more, depending on ergonomics and design.

I think I've already found the desired chambering, in 6.5 Creedmoor, but am still looking at what necking down to 6mm gives me (for one, allowing longer bullets to feed more reliably in semi-autos, it seems).

Second, I'm looking for a 'do anything' super-carbine. This would have Bulk -4 or even Bulk -4* and would ideally be close to the handling of the M4, various shorter 'Recce rifles' or the HK416/HK417 or FN SCAR-L/SCAR-H with the regular barrels. If possible, of course, matching the OAL and handling of something like the CQC barrels of the FN SCAR and HK416/HK417 or the Colt Commando, Mk 18 and similar short M4 types would be magical, but such short barrels would lose far too much velocity.

In a perfect world, it would remain comfortably supersonic until at least 1,000 yards and be able to shoot accurately until that range. If that turns out to be impossible, it still has to beat the effective range of the 5.56x45mm NATO from a 20" barrel rifle, which a number of loadings in several chamberings can actually do, even from shorter barrels.

Obviously, the reason to carry such a weapon at all, instead of a precision rifle, is that it would be lighter, handier, more concealable and more useful at typical short combat ranges. So it needs RoF 3+, Shots 30+ and all that typical assault rifle/carbine good stuff. But because the shooter might well have the ability to make accurate shots at up to 1,000 yards if the mechanical accuracy and the external ballistics of his weapon system allow, it makes sense to think about allowing the carbine carried to have an alternate role as a long-distance platform out to the longest range practical without compromising other desired characteristics.

[1] Technically, I'd also like a third weapon system, a real supersoldier sniper round, well outranging the 6.5 Creedmoor. Semi-automatic, Shots 8-10(3), Bulk -5 (unlikely) or Bulk -6. Magnum 7mm, .30 caliber or .338 caliber.

Originally Posted by acrosome

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.

Agreed.

From 24" and 26" test barrels, 6.5 Creedmoor loads are often accurate at well over 1,000 yards and remain comfortably supersonic until entering the transonic zone at between 1,150 yards and 1,700 yards, depending on the bullet used and how hot the load is.

From a 22" barrel, accurate shooting with several well regarded loadings at up to 1,400 yards, at which time it goes transonic, is well within the realms of possibility (at least as far as the weapon system goes, most human shooters will never care about this level of performance).

Even with a 16.5" barrel, it seems that 1,000-1,100 yards before the bullet goes transonic might be reasonable. I still haven't found good data for shorter barrels than that, probably for the reason that it would require an obsessive enthusiast willing to go through government paperwork for a range toy with little obvious utility.

Originally Posted by acrosome

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

Yes, but what is the best performance I can get at 800-1,000 yards from a 14-inch barrel? And what chambering ought I be statting for that performance?

Look at it like this, I'm statting both the DMR carried by supersoldier marksmen that will be able to make very accurate shots at out to 1,200+ yards (maybe out to ca 1,500 yards) and the carbines that will have shorter effective ranges, but still outrange most weapons carried by human soldiers, because the 'typical' supersoldiers can still shoot more precisely offhand than most human snipers manage from a stable position.