I've found most of the Savage rifes don't pattern the two barrels together. In other words if you have the windage set on the rifle, the shotgun barrel may very well pattern far right or far left.

I owned a Saur 12x12x.243 that had all three barrel regulated well. But as with any quality drilling, you're talking a pile of money.

A friend of mine had a vrilling (four barrel gun) for a number of years.