If you have not had the slide lock back with rounds in the mag when shooting the 10, you should not have that problem with the 40 S&W. However, it could be that one of the bullets from the 40s might be kicking the slide lock up enough to lock back the slide. The magazine floor plate does this when the mag is empty but if you are using the 10mm mags it is possible that one of the shorter rounds (40s) could be activating the slide lock prematurely.
With a 40 S&W in a 1911 I think I would try a 18 lb recoil spring. The 45 usually comes with a 16-18 lb spring but factory springs are so mass produced that one must wonder if they spring tension is consistent. Wolff Springs makes springs, and that's all they make. I would trust their spring weight consistency more than a factory spring.
Barrel tolerance fit specs??? I would say that if it fits well enough to allow manual chambering and extraction (lock back the slide, insert a loaded mag, release slide to chamber a round, manually eject) with about the same degree of smoothness as the factory 10mm bbl then you have a adeqaute fit. However, this might make the real expert gun builders, like SharonAnne, nutz, and I hope she comes back to straighten me out or better clarify your questions.
It could also be that the pistol now needs some more 'break-in' to get the barrel to seat properly in the slide. But I do believe the magazine locking back the slide while it is still loaded may be more a result of the shorter oal of the 40 in a 10mm mag. jmtcw.