Does anyone know if you can swap/convert barrels in the SD line of S&W pistols?  I know that you can readily do this in the M&P series and it works really well, but a friend asked if you can drop a SD9VE 9mm barrel into an SD40VE to shoot 9mm ammo and I didn't know the answer.  Anybody have direct experience with this conversion?

More than likely no you cannot just drop the 9 barrel in a 40 it will require a conversion barrel.

Not much really exist as far as aftermarket support for that line of pistol so it may be hard to come by.

No you can't swap the barrels, the 40 is wider.

Smith and Wesson forums

The barrels do not drop in, but complete slides do interchange on the frames.   SD40VE complete slides pop up all the time on Gunbroker.

I bought a SD9VE and then bought a complete SD40VE slide off Gunbroker and now I can swap them out.

The 9mm frame has spacer rails in the magwell so a .40 mag will have a very hard time forcing its way in there. I used a razor blade from a utility knife and a sharp chisel and cut the plastic spacer rails out of the magwell of my 9mm lower and now I can use both .40 and .9mm mags and slides. If you start with a .40 magwell you do not need to trim the spacers out.

This is the same in the M&P line, but you can use 9mm barrels in the 40 slide.  The barrel hood just doesn't have a tight fit.  40 in a 9mm doesn't work.

Thanks for the info on the frame/mag well.  Very good to know upfront