Maybe a Snub Pistol example

[aramis]

By technical terms the CAR-15 was NOT a submachine gun. One of the key definitions of submachine guns is the use of a pistol-caliber cartridge.

It was, however, used as a functional replacement for the M-3 Submachinegun. There are those arguing that it doesn't, but the role of the SMG at introduction was to provide a shorter-than-rifle weapon for tankers, and as a squad support weapon. The CAR-15 was morphed into the XM177, which spawned the M4 Carbine and GAU-5A ACDW (air crew defense weapon)
The GAU-5A folds... at the breech.

There have been AR15 pistol modifications/variants around for decades. Typically 10-16" barrels, standard AR15 upper and lower, and no shoulder stock or a folding one. Most look much like the XM177

One thing that's not accounted for here is the atmosphere the gun is fired in. Z-G on a starship with a standard atmosphere present will recoil differently than the same weapon fired on a airless moon. Why? Because the gas (assuming a chemical reaction firing sequence) will have different characteristics in terms of expansion and the resulting force from that. If there's no air pressure fighting its expansion, it will have a different force on recoil than if there is an atmosphere present.

Yep. As will deck friction in gravity vs lack thereof in zero-G.

 

[whartung]

Why? Because the gas (assuming a chemical reaction firing sequence) will have different characteristics in terms of expansion and the resulting force from that.

I'm sure there may be some difference, the question is would it even be noticeable.

 

[Condottiere]

Lower barrel - okay, so the snub revolver suddenly makes sense, if you're going to cap ammunition capacity.

And then you have the derringer variant.

 

[Diveguy]

Gas piston isn't going to reduce the felt recoil in zero-G, as in zero-G, the amount of gas escaping is going to generate the same vector either way..

A muzzle brake will reduce, but physically is unlikely to be able to completely compensate even the majority of the recoil.

When you fire a round, the total forces pushing back must meet or exceed the force on the bullet. (That's basic physics.)
The only way to cancel the rearward forces energy are to have energy pulling it forward or to transfer the rearward forces to a larger object. A piston's not going to do that. (It might cycle the Cylinder, tho'. )

Felt recoil is a function of energy over time; it's literally acceleration. And, given that it's off the axis of the support, it wants to rotate the support... we call that "muzzle climb"... A counter-bolt piston could be used to reduce muzzle climb... but the snub as drawn doesn't support that.

For zero G, if you're braced in place, you transfer force normally. If not braced, you're going to convert that force to speed. It's going to be off-center. And it's not going to be that much different between 500J across 0.05 sec or across 0.2 sec. It's still 500 J offcenter acceleration.

Physics-wise, you're not wrong at all sir.

Although, YES, you can compensate for some transferred recoil with a piston and/or buffer assembly absorbing some of that momentum. In fact, it's not a new technology to do so, and firearms like the AR-platform use the buffer tube to do some of this (although it has other functions as well).

No arguments on the Zero-G in real world. I was speaking more to the "handwavium" concept we're inherently looking at in Traveller. We already do it with heat dissipation, detection ranges, FTL, etc - my thought was simply putting it in terms of the snub pistol design and why it might be as such.

 

[Diveguy]

It was, however, used as a functional replacement for the M-3 Submachinegun. There are those arguing that it doesn't, but the role of the SMG at introduction was to provide a shorter-than-rifle weapon for tankers, and as a squad support weapon. The CAR-15 was morphed into the XM177, which spawned the M4 Carbine and GAU-5A ACDW (air crew defense weapon)
The GAU-5A folds... at the breech.

There have been AR15 pistol modifications/variants around for decades. Typically 10-16" barrels, standard AR15 upper and lower, and no shoulder stock or a folding one. Most look much like the XM177

Yep. As will deck friction in gravity vs lack thereof in zero-G.

Don't forget the short-lived abortion that was the M231 Port Firing Weapon for the Bradley.

My point was that terms matter. Yes, the CAR-15 and iterations were built to serve a similar function to the M-3 submachine gun, that doesn't mean they're the same thing. No more than calling the .30 M1 Carbine a SMG because of role.

It's the same as the whole "assault rifle" term that gets thrown around in the US - where, in fact, actual "assault rifles" as defined (intermediate cartridge, select fire, magazine fed) are so statistically small in both possession and criminal use as to not even be a rounding error.