But there is a long answer too. Go to The UL website and do a search on categories QBWY and CEYY. This will give you a list of companies that have boxes listed for use in rated walls. If you follow those links and look at information for various boxes, you will find that many of them are listed for use at less than the 24 inch spacing under various conditions without putty pads.
If you do a search on category CLIV you will get a list of companies that have listed putty pads (known as "wall opening protective materials"). Be sure to look at the "guide information" link in that list. The links to the various companies will give you information on the use of their pads.
also pay close attention to drywall installation restrictions for tolerances in openings, as back-to-back applications are tape-to-tape for blow through, like having open joints back to back.
