Re-visiting here with notes for my own reference as well as for others:
Internal volume of 30 lb R22 is about 1/2 cubes including expansion space (calculated)
Tare weight of bar handle jug at 0psig : 6.13 lbs

About 13oz left at 70 psig (almost 3% of 30 lbs)
2.3 oz at 0 psig
1.2 oz at 15" Hg

On a side note, unopened National brand 410A (25 lbs) was found to weigh 33lbs 6oz