The fellow with whom I spoke in one of the armorer recerts mentioned that in the original M&P's the slide & barrel started to unlock when the bullet was typically only up to several inches out of the muzzle, but in the 2.0 the bullet is significantly further. He offered some numbers, but I don't think I wrote them down, as that sort of trivia is unnecessary from an armorer's perspective, albeit sometimes interesting trivia for owners and enthusiasts.
I'd also not be surprised to discover that sometimes a particular set of tolerances might produce some unexpected issues that are better addressed with some different parts, like a new barrel, perhaps. Or some revised specs/tolerances (new twist rate?). Remember reading about S&W replacing barrels now and again when guns were sent back for complaints about horrible accuracy?
Also, remember that delayed unlocking was something the engineers introduced in the metal-framed TSW's, claiming that it also helped reduce felt recoil compared to the standard 3rd gen's.
Lots of folks like to talk about "match-grade accuracy". The M&P, like the Glock and most other
standard plastic pistols, was designed as a service-grade gun.
Longer, heavier slides and slightly lighter triggers in some of the "Practical", "Pro series", etc models may make guns easier to run in some competition venues, but it's not like they advertise them to be able to consistently produce groups of less than 2" at 50 meters.
There are probably always going to be compromises involved in deciding whether someone wants a "combat/service" pistol capable of excellent reliability, especially under adverse, extended conditions ... or a comp gun built to tolerances that are much, much tighter, capable of match-grade accuracy, but maybe not able to always run so well in less-than-optimal conditions.
I'll offer that today's engineers and engineering, with CAD and advanced CNC capabilities, are offering us some phenomenal advances over the state-of-the-art for standard/service grade pistols I was owning and using through the 70's and 80's.
