Ok, a bit of guns stuff - lovely...
What's interesting (at least to some of us) is how conservative the US have been for some years as far guns are concerned. Having settled on gatlings in the 1960s, they have stuck with that basic design since. The core of the current M61 can be traced right back to 1930s designs or even earlier. They have always valued a high sustained rate of fire over just about any other parameter, and their aircraft have been large enough to carry the guns (and large ammo tanks) that resulted. The other side of the coin is that they have not, for many years now, had many teams capable of designing a decent gas or recoil powered gun or cannon. Mind you, nor has the UK - we are still using 1930s technology Browning M2s).
The Russians, by contrast, took a very different approach, and have appeared to go for guns and cannon that are as self contained as possible so that they can be used in a variety of platforms. They have also had very talented design teams that could produce clever stuff. So, self powered gatlings....
The 'Hind' was, for many years, armed with a 4 barrel .50 calibre gatling in the chin turret - the Yak B gun. It makes an interesting comparison with, say, the M3M .50 Browning design we still use. Lighter, fabulous rate of fire, and ever so simple - but clever. Basically, ports in the barrels allow gas to be tapped off to drive a sleeve around all four barrels that moves fore and aft - working a bit like a pump screwdriver, this sleeve then rotates the barrel group to feed new rounds in, and the gun stays going. It's started by a coiled spring up the centre of the four barrels, and if that doesn't work, there are three starter cartridges fired electrically to get things going.
The bigger russian gatlings show, however, that staying self powered brings problems. The challenges of using gas power at 23mm and then 30mm are FAR harder than at 12.7mm, and there are big issues with recoil loads and other stuff. They were not able to simply 'scale up' the 12.7mm design, and the larger gatlings had reliability issues as well. If you don't go with multiple barrels, then revolvers are need for high rates of fire. But, revolvers can be very hard work to make effectively, which I believe is why the US have stayed with the Gatling.
So... the russians went for a gas powered design in the Flanker, but discarded revolvers and went for a more conventional 'linear' design with a fore and aft moving bolt and breech. It's a bit like a 30mm GPMG. They sacrificed muzzle velocity and rate of fire in favour of a heavy 30mm shell, and I have a suspicion that they have some form of advanced gunsight to improve kill probability. But the biggest win is weight - the gun weighs just over 100 pounds, and is called the 'Ballerina' - slim, light but powerful.
There IS a half way house, and that's the larget gun ever fitted to a helicopter - the Russian twin barrelled Gsh-30-2 automatic cannon fitted externally on some Hinds. One gun, two barrels, operated by combination of gas and recoil, huge great 30mm high velocity rounds like the A-10. And weighs a fraction of the A-10 gun.
You may have guessed that I am a bit interested in this stuff - mainly because it's an area where you get a lot of interplay between requirements, technology, pure engineering, dogma and politics. The decision to remove the gun from the Harrier GR5 and then the Typhoon was driven by one RAF senior officer who had decided that 'guns were outmoded'. The debates on the F-35 programme over guns were no less emotive and not much better informed.
Courtney, hope this helps a bit
Best regards
Engines