Thing is, like the M85, the M2 can be fed from either side, but the gun mounts are built to carry an ammo can on the left side only. One quick-and-dirty answer would be to add on a mount for a Russian PK MG on the other side, since they use a righthand-side feed, unlike the US M240, M60 and M249 MGs. There are Navy/Coast Guard twin-.50 mounts that could be copied and fielded, but for use inside a turret, the M85, designed for that purpose, would be a better pick, since it also has a quick-change barrel and a lo/hi rate of fire [500 RPM/1000 RPM each gun- think about 4 of THOSE on a quad .50 mount....] I'm not sure which link the new M312 .50 MG is supposed to use. But supposedly, pasrt of the problem with the Stryker's Remote Weapons System is the ammunition coming partially unlinked in the feed tray as the vehicle moves down the road, from vibration. The M9 link of the M85, which has a tab that snaps into the cartridge case's extractor groove, like a 7,62mm M60 or M249s M13 link, might solve that problem too. And if it did, it'd not only be a quick fix for the Strykers .509 teething problem, but a cheap one...and one that'd add to the firepower [1000 RPM on fast rate] as well. Until the 105-round ammo can rubs out.
But that's still better than a jam in 45 rounds or less.
-archy-/-
One of my uncles crewed on a White halftrack with a quad-50 anti-aircraft mount during his European vacation from Normandy to the Rhein. He said they never had a crack at any Luftwaffe planes--none came close enough---but used their vehicle mostly as direct fire support for grunts. I gathered that it was a bit intimidating to be on the receiving end of four Ma Deuces at once.
Apparently their ride was pretty reliable. Seems like he said their biggest problem was torn up tires from having so damn much shell and bomb fragments to run over--that and almost freezing their 'nads off in the 44-45 winter. But it sure topped being a grunt :]