I had just sent a note to Bill K about a 4.6X30MM case I just necked up to 20 caliber. EASY transition and it looks real good too.
You'll need to build a dummy round for specs, ship it off and have a reamer cut, then invest in a 20 caliber barrel to be chambered. Just a matter of investing more money.
Makes going with a factory round like the .221 Fireball look better all the time.
Going to the 20 VT is pretty easy. You'll need a reamer to cut a chamber in your chosen barrel. Then you'll need dies. Brass is pretty easy to come by. I just take my fired fireball brass, neck it down to 20 in the VT die and it's good to go. And as mentioned, when you drop down in caliber, pressures jump up REAL FAST!! So you end up starting all over again. More to learn.
Once you have to beat your bolt open on an over pressured case, you just learned the hard way. Better than having to replace your gun or seek medical attention.
