My Delta Elite is on its way back to me as we speak, after spending some time at the Colt Custom Shop.  Among other things, I had a .40 barrel fitted and is coming with one Wilson mag.  I expect to use a different recoil spring with it.  Don't know, yet, if the .40 barrel will have its own bushing.  I loose too much brass shooting action pistol during the summer, and I have close to 5000 rounds of .40 brass, so. . .  Brent says it runs like a scalded dog with both 10mm and .40 and is as accurate as all get out, so am anxious for the Fed Ex truck to stop at my house!

To the OP, I would say to get the most out of your .40 barrel, have it fitted by a good gunsmith.

If you want some slower loads for general plinking, Universal Clays works well and meters just fine through my Dillon.  but for full power loads, I like Longshot.