I have a beat up S&W M&P 38 & a star BM I was thinking about giving a new finish to. how far do I have to take these apart before using duracoat shake n spray? I just don't  want any binding issues or stuck parts.
thanks

IMHO. Pass on the rattlecan on the 38.  Go buy the Duracoat that you need to mix with hardener and thinner.  Get a $10 air brush kit from Harbor Freight and a Can of Air from Hobby lobby. You can spray a thin coat with it.

You will need that on the Cylinder on the 38.  If it is too thick it might cause problems with cylinder rotation.

The BM Just take out the Extractor and Firing pin.   Leave the Sights.   The Frame it isn't had to remove the hammer and thumb safety as well as the magazine release.

Use duct tape to tape off the rails on the frame.

I use Cleaner from Dollar Tree called Awesome Cleaner?  Yellow stuff in a spray bottle. Use a tooth brush, q-tip, scotchbrite pad and hot water to get all the oil off the gun.