Plastic tip pellets are a gimmick to sell pellets to airgunners who don't know that they are not as good for accuracy as round nosed pellets, especially as distance increases. There are various shapes and head configurations in airgun pellets and most pellets are comparatively accurate at shorter ranges. In 10m airgun competition, for example, flat nose pellets are used because they punch clean, round holes and as a result are easier to score. Other designs, such as "pointy" pellets and hollow points are less accurate than the standard round nose pellets and this becomes more and more important as distance increases.
In any event, with the relatively slow speeds of airgun pellets, its doubtful that a plastic tip on a hunting pellet makes a significant difference in pellet expansion upon striking quarry at longer ranges.
I just quickly browsed the offerings of a couple pellet manufacturers (Gamo and RWS) and I'm not seeing anything in the literature to suggest that plastic tipped pellets confer an accuracy advantage. RWS does not even offer a plastic tipped pellet. They do, however, offer a pointed lead-tip hollow point. The advantage of these designs are, according to the manufacturers, focused on terminal ballistic performance, particularly with reference to penetration. Given a lead pellet fired from an airgun is a relatively light and low speed projectile, it does make sense to have a pointed tip to aid in penetration, as the pellets simply do not have the supporting mass behind them to punch into all intended live quarry targets with the other, wider tipped designs. As to whether the tip makes a difference in expansion for airgun pellets, that doesn't seem to be the primary design intent. In centerfire applications, it is also debatable whether or not a tipped bullet offers greater expansion compared to a conventional hollow point. It seems to be intended to provide a combination of penetration and good expansion at extended ranges and the subsequent lower velocity of the projectile. Obviously, nobody is taking 500 yard shots at game with an air rifle... nor are plastic tipped pellets a direct comparison to a ballistic tip centerfire bullet, but what I am seeing for both is that blend of penetration and expansion.
Does the shape of a bullet affect its cycling in a semi-auto? I don't know. For whatever reason, there aren't any "ballistic tip" .22LR or even Stinger rounds available, are there? It's certainly not because no one at the ammo makers never considered the idea.
Yes, the bullet shape certainly can affect cycling in a semi-auto (and some bolt actions, for that matter, I've had the flat nosed Eley hang up when magazine fed in my CZ 455). Narrow, pointy bullets should feed more reliably in any action, as they afford more clearance for the bullet nose over the magazine lip and feed ramp of the rifle. My father's Remington 7400 .270 rifle notoriously jammed when attempting to feed soft point ammo from the magazine, with the larger nose of the bullet catching on the feed ramp. A switch to ballistic tip ammo solved the issue, as the extra couple mm of clearance allowed the nose to pass over the feed ramp, and feeding was smooth from there as the side of the bullet will not catch on the ramp.
Ammo makers will certainly entertain any idea that will help them sell more ammo, won't they? Case and point with the new SK Long Range Match
That's a gimmick if there ever was one. I'm sure ammo makers have floated the idea of ballistic tip .22 LR ammo, perhaps even prototype tested it as well, but likely found no advantage in either external or terminal ballistic performance to justify the manufacturing costs for what would likely be a niche, low-volume market. As .22LRGuy points out, hollow pointed ammo does what he needs it to.
