Duracoat will not burnish with use and will wear badly on load bearing surfaces. By "wear badly", I mean that it will flake off. To make matters worse, the flakes are large enough to gum up the works. Duracoat aka Polane was never intended as a finish on wearing surfaces.
This photo shows the worn off flakes of duracoat aka Polane built up in internals areas of this SIG.
A "wear in" finish like Gunkote or Molly Resin will burnish to a matching fit. Burnishing means that it will wear without flaking or peeling. Gunkote or similar finishes can be applied to all of the internals, slide/frame rails, barrel exteriors, etc. with no problems since it will burnish to a perfect matching fit.
SIG's lock up pretty tight on the barrel near the muzzle and will show wear there pretty quickly. Unless your barrel is rusty, duracoat aka Polane can and will make it worse.
Duracoat aka Polane may be fine for some things (dump truck & garbage truck sides, traffic barricades, etc) but it was never designed as a finish for the close tolerance parts found in a firearm. Keep yer powder, Mac.
Tuff-Gun Finishes. The Name Says It All.
Mac's Shootin' Irons
http://www.shootiniron.com