It wouldn't work.
When you fire off a ball, it has reached maximum velocity by the time it has reached the last few inches of the barrel. When a ball is fired through the flatline (attached normally, not on the end of another barrel) the ball is accelerated through the flatline and is given backspin (magnus effect) which allows it to "float" further downfield. The ball rolls along the top of the curved barrel WHILE accelerating out the end of the barrel.
Trying to shoot with the setup as illustrated in the OP, would basically be firing a ball into a flatline, and the ball trying to bounce around inside the curved flatline pipe. I think it would be an exercise in futility, and a messy one at that.
But, I have been proven wrong many times in the past. Give it a go.
If you do try it, can you take video footage of the maiden voyage? I'd like to see that.
