Well hell, fellers, old Henri Pieper back in the 1880s-90s had his 7-barrel goose rifle in
.22 and .32 rimfire.* It was a single shot rolling block, but with sheet metal speed loaders
probably pretty fast at taking geese out to -- what? 200 meters? Market hunters in those days
(God blast and damn their souls if they had any) weren't bothered by cripples.
Until infantry squads can carry 35mm autocannons in their rucksacks, we might want to
think along Pieper's lines. An extended length 40mm munition for grenade launchers (break
action types, not slide actions I fear) incorporating, say, nine .22 caliber rifled barrels preloaded
with the highest pressure cartridges feasible, could augment the squad's loadout for trips
into FPV country. Three men with underbarrel launchers could keep up a pretty steady fire,
at least against single targets.
Yes, Andy, they could be adapted to use the highest-tech rifle sights money can buy.
* Again, I'm sorry I can't post a link. But Google is still our friend.