In the future will we see grunts use 50cal assault rifles that use telescopic ammo?
The main feature of telescopic ammo is its compact shape, which is not really very relevant to small arms.
Very simply, if you look at the 12.7mm round, it is a metal tube with a bottle neck and a projectile that sticks out the front.
ie:
The projectile sticking out the front makes the entire round quite long but more importantly it makes it an odd shape as it is narrow at the front and wider at the rear so there is a lot of wasted empty space around the front of the round that is just empty space.
Very simply a telescoped version of this round would take the original dimensions of 12.7 x 108mm and move the projectile to inside the tube case that is slightly lengthened... so say a 125mm long case that is a pure cylinder with the projectile inside.
For the armour piercing round that internal projectile will be a long narrow dart shape with a sabot to fill the barrel tube, so the standard AP round will be APFSDS. The standard ball round will be similar to the standard ball projectile, but when you stack these rounds that are pure cylinders there wont be any wasted empty space at the projectile end. Using more modern and more powerful propellants the round might even be actually shorter than the original case length of 108mm, which makes the new round much more compact as the original rounds case was 108mm plus the length of the projectile.
Another advantage of telescopic rounds is that if we take the example above of a telescopic version of the 12.7 x 108mm... if the shell case was 17mm across at the base then a weapon designed to fire the original rounds in 12.7mm calibre would just need a slightly larger calibre barrel to fire new 16mm calibre projectiles using the same gun, the same ammo feed, the same bolt the same everything... except of course the slightly larger calibre barrel.
The difference in not huge in 12.7mm calibre, but imagine a large round like the 57mm round used in the S-60 gun...
Without measuring precisely using the 410mm long case of the round next to it the 347mm case of the 57mm round... the gap between the top of the case to the top of the case of the 410mm is about 60mm and with your fingers and that gap you can measure about two of those lengths as the rough projectile length of the 57mm round beyond the shell case.
This means that the 57mm shell has a 347mm long shell case and the projectile sticks a further 120mm beyond that so you will be needing at least a 460mm length space to store a round. Note also that the shell case is much wider than the actual calibre of the round.
Converting this round to a telescopic round you could probably make the shell case slightly narrower, yet extend the case to about 380-400mm with the projectile contained inside the case. This make the round smaller and more efficient in size, yet with modern powders and explosives and AP penetrators you will have a much more powerful and more effective round.
With the change of barrel calibre you could later upgrade the round to a 65mm or even 70mm calibre for a larger HE round.
Another important factor is that the larger the calibre the more energy you can push down it without the problems of bore erosion.
This means whatever performance you can get from an APFSDS round in 57mm calibre, you can get even better performance from a 70mm calibre version... with a change in ammo and barrel.
Obviously it would be critical that you make it so that you cant load a 70mm round into a 57mm gun... perhaps a small cutout at the front that wont allow 70mm rounds to be properly chambered in 57mm guns would be the best solution.
BTW how is the Ash-12,7 light enough to be handheld?Does it use ultralight materials?
The ASh-12 does not use standard 12.7 x 108mm rounds. It uses a special 12.7 x 55mm round in both subsonic and supersonic varieties.
It is a manual loading weapon... a straight pull bolt action, so it does not have a gas system... which probably saves weight.