I don't see why it wouldn't hit a usable velocity, it just may not be super efficient.
I really like the very feed, you rarely see a vert hopper feed Sheridan, I think they look great! About the only ones I have seen have been Semi auto conversions.
Is the seam on the barrel where it is spliced together or just a finish mark? I know you have lots of tricks up your sleeve so that seam I see on the barrel makes me wonder. The stepped bottom tube looks pretty cool too