This will workI say yes as I have a M7 in 17 fb and it feeds just fine, so a vt should work also
I think you would be fine then with a center feed magMy action is actually a Defiance Model 7 length. It has an M16 style extractor. It is in a similar location as the 221 FB. The ejector is positioned in the center of the other bolt lug instead of at the bottom of it.