Gary: I don't have much use for a F/F setup, at least on a hunting gun. Knowing only as much about your gun and intended use as you've shared here, I'd suggest you open the bottom barrel (I'm guessing this is an O/U) to Skeet 1 or IC and leave the other barrel alone for a season. It will be a more practical setup and make the gun more valuable to most future owners. If your Merkel is like the one I owned, those original bores are very tight. Have you measured them? TT

"The very acme of duck shooting is a big 10, taking ducks in pass shooting only." - Charles Askins