I had an awesome fantasy today: what if someone took a Noreen Bad News .338 Lapua Ultra Long Range Rifle (http://www.onlylongrange.com/badnews.asp) and scaled it down to a close-range/checkpoint rifle? Please try to refrain from telling me how impractical and ridiculous this is; I am fully aware. I just think it would be a really cool experiment that would once again exemplify the versatility of the AR platform. The .338 Lapua Magnum cartridge has incredible accuracy, penetration and knockdown power. Noreen had a really cool idea when they made a semi-automatic precision rifle that utilized the .338, and I think it would be really cool if that same technology were used to make a PDW variant. Lethality would no longer be an issue at checkpoints, as well as other anti-material, close-quarter scenarios. Sure, you can argue that the .458 SOCOM and the .50 Beowulf have the edge in portability and practicality, but can they be counted on to accurately engage targets past 200 yards? The .338 Lapua can easily do that, even with a super-short barrel. Again, this is just for fun. Bear with me for a while.
1. How short can a .338 Lapua barrel be? You know, before you start getting serious ballistic issues. I know that the Desert Tactical Arms Stealth Recon Scout Covert (DTA SRS Covert) was originally offered in .338 Lapua Magnum, and that rifle had a 16" barrel. I'm sure it would be possible to go shorter than that! I would love to be able to go as short as possible. Does anyone know how short that could theoretically be?
2. I don't want to get into a DI vs Piston debate, but I think that for this particular setup a short-stroke gas piston system is the better call. It's what the Bad News uses, at least. I don't know enough about the .338 Lapua to know how long of a gas system it would need for a DI setup, but I think it would be especially dangerous in an SBR configuration, reliability-wise. If the 5.56 gas tube starts acting up once you go shorter than a 10.5" barrel, think of what the .338 would do under similar circumstances. LWRC, POF, Robinson Arms, and Adams Arms all make ~7" SBRs, and they all use utilize a piston system. A piston is just safer for an untested setup.
3. The muzzle brake would have to be very effective at taming recoil. I can only imagine what shooting this thing standing up would be like. It would be very loud and flashy as well, but remember that this is not a design centered around practicality.
4. The stock, unlike the Bad News, would not be a PRS-style design. More like a Magpul CTR. Something very compact and lightweight. I also don't think this weapon should have a quad-rail either; it's gonna be unusually heavy as it is. The fore end should be as lightweight as possible to compensate for the heavier magazine, ammo, etc. Think of the NGA X7/X8 and you'll get the idea. This rifle doesn't need to be overly customizable; it's just a giant boomstick.
In conclusion, this setup would be possibly one of the most specialized AR-style weapon systems on the market. In other words, it would suck at everything except a few key areas. It wold be a badass PDW, capable of taking out threats well beyond the range of current models. It would also be able to thoroughly penetrate body armor (even Dragon Skin, possibly), as well as vehicles, cinder blocks and sandbags. The .338 Lapua Magnum leaves nothing to be desired when it comes to lethality.
Am I just way out there? Or does anyone else think this would be cool? Not practical, mind you, but cool.