I googled, went to LWs website, read at least 3 reviews, etc.I did your Googling for you.
16", same as their regular barrels.
And this helps just how?
1 in 12It was not very easy to find, I just had the time to fool with it. I should have linked the location, but I didn't and I don't want to repeat the search.
I note that Apex is having Plastic M&P barrels made up by Barsto with 10 twist. They say that the torque reaction of the fast twist firms up the lockup and improves accuracy.
I finally found out what the difference is between a Sig P210 standard barrel and their "lead bullet barrel." The standard has a 10 twist, the lead bullet special 20.