So I don't know where that leaves you with short stroke. I honestly don't know the advantages and disadvantages it has, or why it's considered "the best choice" by the people actually out to win contracts, while DI and long-stroke are exclusively relegated to ARs and AK knockoffs. Anyone know why?
As a somewhat educated guess, advantages of a short-stroke piston are:
- Can be made less sensitive to variations in ammunition. This was first put into practice by "Carbine" Williams, when he invented a tappet gas system. That said, most modern rifles use a gas regulator, so this advantage is not fully utilized.
- Can be easier designed for field-stripping. I would say, Russians were pioneers of it. Tokarev's 3-part short-stroke piston was widely copied, in particular by Germans in G-43. Although, of course, everything can be screwed up. Look how much easier it is to disassemble AK than SKS. One way or the other, a long-stroke system has to be designed so that a long assembly were possible to extract from a receiver, and the short-stroke system does not.
- As was discussed
extensively in this thread, a smaller reciprocating mass helps recoil mitigation for full auto, if it's a design objective at all, of course. Note, by the way, that machine guns tend to have long-stroke systems in part because there's no need to aim their bursts as precisely.
- Although it is no longer a consideration, a short-stroke piston does not conflict with loading by stripper clips (well, conflicts less - just recall how much effort John Garand spent on designing the machine that bent oprods). My recollection is somewhat vague, but I think it was a factor in the design of FAL, which inherited its gas system from SAFN, which was strip-loaded (IIRC).
- Finally, a short-stroke system offers a significant advantage in accuracy when shooting in single shots. I'm sorry to say, this was always a bit of a mystery to me, because the bullet exits the barrel long before either long- or short- stroke piston starts to move. However, it's pretty much a fact. Memoirs of various people all agree that it was a major factor why Dragunov selected it for SVD.