It's apparently enough of a difference that there are no 10mm chamberings in 9mm sized platforms...2.31mm difference between 10mm and 9mm, really doesn't add a whole lot. Magazine capacity is the exact same as 357 Sig/40S&W.
Last time I looked Academy only had one kind of 10mm and it was way overpriced.....but that may have changed, dunno'.10mm ammo availability isn't a big deal in OKC, you can walk into Academy or H&H and get it without any problems.
For the folks that do not live near one of those places, they are pretty much screwed unless they handload or order online.
But....the 357sig penetrates better than the 135gr .40 offerings, and that is one of the reasons that police agencies like it.I see no real advantage. If you want to shoot a light bullet get the 135 gr .40 S&W. Of course the bullet weights are a little heavier in the .40 so no real direct compassion. I like heavy bullets not lighter....JMO
From the double tap wide site.
357 sig 125 gr. 4" bbl - 1450 fps 584 ft/lb
147 gr. 4" bbl - 1255 fps 514 ft/lb
.40 S&W 135 gr. 4" bbl - 1375 fps 567 ft/lb
155 gr. 4" bbl - 1275 fps 560 ft/lb
I've found the 135gr .40 loads to have more recoil than any of the 357sig loads I've tried.I have and I disagree. Not a whole lot of difference. Lighter bullets recoil less with the same powder same dia bbl. The loads make the difference and you can't get more powder in a .357 sig round since it's a 40 necked down. Really physics don't lie. Same powder in both the .357 sig will have more presure generated just like the presure in a large water main compared to a smaller dia. pipe.
You're right..physics don't lie...and the bottleneck design produces different flame front characteristics which does have an effect.
But, back again to penetration...
The 135gr .40 loads may be good performers directly in bad guys, but I don't have much confidence in them vs. intermediate barriers.
Now, maybe if they utilized sturdier bullet designs in those loads....
The common .40S&W 180gr loads are identical ballistically as the FBI's spec for their formerly issued 10mm.I'm just saying there's hot 40 S&W if you want something hotter than plain Remington 40 Short&Weak.
Personally if I want something hotter than the common 165-155gr loads, I'll just switch calibers.