I had the same problem with my Winchester 96 12 gauge O/U. Remove the butt stock and open the action slowly; the ejector for the bottom barrel will kick before the action is opened far enough to cock the bottom barrel.
I was easing my gun open to catch the empty shell at the trap field and frequently (about 20% of the time) had subsequent FTF of the lower barrel. Now I deliberately open my gun fully and it only occurs about once in 6 or 7 rounds of trap.
Winchester 96 and (original) 101 were made by Olin-Koshenda in Japan.
Bob
