The ammo you are referring to is for snakes. You'll often see it referred to as snake loads. It is only effective to about three to for feet because the shot is encapsulated in a plastic capsule (kind of like the old Contac cold medicine capsules---remember those?) and the rifling imparts a spin to the capsule and the shot does a swirling spiral out the bore. That's why shotguns are smoothbores. The round is intended for folks who encounter snakes so close you cannot escape them and your only hope is to shoot the snake without risking a rebound, richochet, or a miss (a miss that would then, theoretically, upset the snake more, thusly ensuring you got bit.) I've done a lot of experiments with snake loads and never seen them produce a consistant pattern past four feet. There will usually not be enough recoil from a snake load to reciprocate the bolt or slide on a semiautomatic weapon. Even further, the plastic cpsule will often crack on the feed ramp and spill "dust" shot (usually #9 or smaller) into all the nooks and crannies of the weapon. Truth be known, snake shot is best used in a revolver. Most woodsmen load one or two chambers of a revolver with snake loads and the rest with appropriate loads for two or four legged predators. Of course in winter, the snake loads become unneccesary. If you are in heavy snake country, I would think you would be better advised to carry a .410 "snake charmer"; that is a cut-down to legal limit single shot .410 shotgun. I know that in Southern California wilderness areas, rattlesnakes are very thick. Cabela's has snake boots for $129 a pair and I would suggest those as well. Sankes, though, are very shy creatures who hunt primarily at night. You might see them during the day sunning themselves, but they will often give warnng if you walk slowly and with consideration as to the other denizens of the locale. I will say this, though: If you are close enough to a rattler to need snake shot to escape, you are absolutely going to get bit if you move your feet an inch. You might get bit making a play for the gun. Most people who get bit either step on the snake (again, not looking where their feet are going) or by climbing rocks and putting their ands into an area they cannot see.
One more thing is that there used to be .22 rimfire shotshells that were called "bird loads." One thing to bear in mind about so-called "bird" loads is that nearly all passerine birds (songbirds) are protected by Federal law (The Migratory Bird Act) and may not be used for "target practice." To do so is a felony and is punishable by imprisonment.To illustrate this point better, a raven is a passerine and is protected by the Migratory Bird Act. So is a blue jay.
Anyway, that's what I know about them.
Those that beat their swords into plowshares will plow for those that don't