I've been busy in the Blow Tube making also......
One for the Rolling Block
And one for the Sharps and 1885 Winchester
I started out with a 45-70 case as Mac describes in his article. And a 44Mag case is used to step it down to the plastic tube.
First, drill out the 45-70 case to the outside diameter of your 44mag case
Then drill out the inside of the 44Mag case to the major diameter and grind most of the rim off the case. Leave a very little lip so it won't pull out of the 45-70 case.
Slide the 44Mag into the 45-70 and super glue the seam (or you could just as easily solder it) It is a very tight fit and Super Glue will hold it fast.
Slip a piece of 3/8ID plastic hose over the 44Mag case and you are done. You might need to heat the tubing up a bit with a low temp heat gun as it is a very tight fit on the 44 Mag case.
For the Remington Rolling Block I had to make a modification because the 45-70 barely fits over the hammer on these rifles with out the extension. So it needed to turn a corner.
A short piece of copper tubing bent 90 degrees and super glued into the 45-70 case solved this issue.
At the other end I built up the diameter of the copper tubing with a 38 Special case and a 41 Magnum case. One inside the other. Super Glued together.
Now to go moisten some black powder fouling!