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that's not what long stroke actually means.
I just like to stir the pot a bit. Rather than further hijack the excellent XCR to SCAR-L comparative review thread, I decided to start fresh.

It sounds like you (Mikey) might ascribe to the definition "long stroke: piston moves the same distance as the bolt carrier (or just operating group), whether it's attached or not." I know this is a very common definition, and it makes good sense. I have yet to find the source for this definition, though.

For discussion's sake, the alternative definition is along the lines "long stroke: piston moves under pressure the same or nearly the same as the length of the operating group." ...where the key words are "under pressure". This definition also seems to make good sense.

And for comparison, the former (like Mikey) would say "short stroke: piston moves less than the distance of the operating group" (or perhaps some percentage less?), and the latter would say "short stroke: piston is under pressure less than the length of the operating group, and the rest of the group's movement is due to momentum."

The key difference is really the definition of stroke. Is the piston's movement itself the stroke, or is the stroke merely the distance that the piston is being accelerated? Both seem reasonable. Both have supporters, though I imagine that more people ascribe to the former.

Most rifles are generally agreed to be long stroke, like the Garand, or short stroke, like the M1 Carbine or AR-18. The discussion seems to center around the AK and the XCR, as both the former and latter sets of definitions would include these two.

So, is there a mechanical engineering dictionary we can go to to determine which is actually correct? Do other dictionaries agree? Chime in; lets see what comes to the top.
 

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No idea but basically a short stroke involves a short tap to the operating rod which then imparts momentum to the bolt group and drives the action rearward. the movement of the piston stroke is usually shorter than the cartridge and in many cases is 1/2" or less.

Long stroke involved the whole piston moving back as a part of the reciprocating mass. with a long stroke the piston and oprod are usually one piece and fixed to the bolt carrier.

The pressure increases in the system while a bullet is in the barrel, once it has left the pressure usually decreases and whether the piston is continually driven by pressure or momentum depends on the gas system. Is is a relief systsem where excess gas is vented as in the FAL or is it a captured gas system like the LW etc... ( Most gas systems vent to some degree)
 

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No idea but basically a short stroke involves a short tap to the operating rod which then imparts momentum to the bolt group and drives the action rearward. the movement of the piston stroke is usually shorter than the cartridge and in many cases is 1/2" or less.

Long stroke involved the whole piston moving back as a part of the reciprocating mass. with a long stroke the piston and oprod are usually one piece and fixed to the bolt carrier.
Simple. There is some retard revisionist movement trying to redefine the AK action as short stroke because the gas only hits the piston head for less than a second, or something equally inane... ???

Long stoke, Piston and carrier connected and moving in unison

Short Stroke, piston and carrier not connected, piston transfers energy to carrier to cycling the weapon
 

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I've always used the terms to reference how far the piston travels in relation to the carrier.

In an AK, or XCR, the piston is attached to the carrier, and travels with it through the full length of a round cycling the action. "long stroke".

In a rifle like the FAL, the piston is not attached to the carrier, and stops moving rearward before the carrier does. The piston imparts motion to the carrier, but then the piston stops moving rearward. The carrier continues moving rearward to its rear-most point without the piston. "short stroke'.
 

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All correct, I'm just not sure if there is one definitive description.
 
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