Originally Posted by robkarrob

Sorry Lost Lake, but the bolt face is the same for both models. There is only .035 inch (1/32 inch or 1/64 inch per side) difference between the diameter of the cartridge rims. The slides are exactly the same except that the width of the slot, where the barrel tang fits. This slot is at the top rear of the bolt face and is narrower on the 9mm slide than on the 40 slide. The slide markings are different (Shield 9 or Shield 40). Everything else is the same, extractor, ejector in the lower housing, recoil springs, etc. 40 into the 9mm will work with just a little metal removal from the tang on the 40 barrel.

The following photos show what area on the 40 barrel needs to be reduced, so it will fit into the 9mm slide. You grind the tang, on the 40 barrel, so it will fit into the 9mm slide opening, which is narrower than the 40 slide width opening. The fit is even better than the 9mm barrel swapped into the 40 slide, since by grinding the tang, you make the 40 barrel a perfect fit. There is a little extra side to side play with the 9mm barrel in the 40 slide, as you can see by the photo dimensions. This extra play does not cause any issues in the 40 to 9mm swap, and does not affect accuracy at all. Your width should be similar to mine. The 40 barrel needs to be reduced .026 inch, .013 per side. Then the 40 barrel will drop into the 9mm slide. All else works perfect, recoil springs, extractor, and the ejector. Then all you need are the 40 magazines.