breechface width?

[greatgoogamooga]

In an earlier post I was diagnosing feeding problems with a 10mm barrel I'm installing on an essex slide/frame. I'm replacing the barrel and while mulling this over in my mind, it occurred to me that the slide is made for a .40 S&W. I know they are supposed to have the same breechface, but the .40 has a rim diameter of .424 and the 10mm's diamter of .425. How wide does the breechface need to be for the 10mm to feed properly?

Maybe I'm just losing too much sleep over .001"

Goog

[1911Tuner]

Don't know much about the 10s and .40s...but I'd want the breechface guide walls to be about .010-.012 inch wider than the nominal print diameter of the cartridge rim.

[stans]

Breechface is the same for 40 S&W and 10mm.