Cool indeed but a few differences to what I was thinking. Those
mods use tiny batts due to the size the builder was going for...I was intending to use an
actual .50 BMG casing rather than the lathe machined aluminum he went with.

The .50 BMG casing alone can hold an 18650 with room to spare and that doesn't include the "bullet" aka mouth piece. A .50 BMG is almost 5.5 inches long from the tip of the bullet to the bottom of the casing and has an interior diameter of about 3/4"! In that picture I posted, the 3rd from the left is the .308 Winchester that JR based his design from...the one on the far left is the .50 BMG

For comparison to a PV, that's 1/4" longer than my 1000mAh Inferno with a 3.5mL clearomizer with a swisher sweets style plastic tip on it and also more than twice as wide.