I watched a guy load a full 15 round magazine with empty .357 Sig brass. He then inserted the mag and proceeded to pull back the slide fifteen times while empties fed into and then ejected with not a single jam. I would say the bottleneck cartridge has the least chance of feed related jamming of the two. Also, some of the loadings for .357 Sig make truth of the original concept of making an auto version of the .357 magnum. If the gun is made strong enough to handle it then it will reproduce some of the warmer 125 gr .357 magnum loadings just fine. The trouble lies in the fact that most of the guns chambered in .357 Sig weren’t originally designed for that much recoil. So some of the guns started to eat their frames.

BUT…

With modern bullets and powders there are plenty of 9mm, .40SW, and .45ACP loadings that are testing in ballistics gelatin tests that have penetration and “wound cavity” channels very similar to the 125gr .357 magnum when viewed side by side. So the .357Sig may be doomed if only by a why bother kind of attitude. That is why I think its biggest benefit may be the ease of feeding from a magazine. It does need a proper bullet selection though as not just any 9mm bullet will seat correctly on the short neck.

Oh, and I find the Lee Bottle Neck .357Sig Factory Crimp Die finishes off the loading of this ammo to near perfection.