When I bought my Comanche this summer the prior owner handed me a Scott Aviation Executive Mark I oxygen tank. It had last been hydrostatically tested in 1972, and it leaked around where the valve goes into the neck of the cylinder. I've had the tank hydro tested and fixed the leak. I've filled it with oxygen and it's been sitting in my bedroom for a month observation period holding 1,800 PSI without evidence of leaks.
I now want to calculate how long this tank will last per person at various altitudes. Unfortunately, I'm unable to figure out the internal volume of the cylinder. I've searched the internet for hours and found no definitive answer.
The cylinder is about 18 inches long and has a diameter of 3.5 inches. It's made of steel (DOT-3AA2100).

Can anyone please help me out by telling me what the internal volume of my cylinder is? There must be a table somewhere listing the various size cylinders Scott sold at the time and their volumes. I believe that the cylinders had different letter designations. I know, from photos on the internet, that size "A" is smaller than mine, but I can't even find out what volume "A" sized Scott cylinders hold.

I've roughly calculated that the cylinder may hold approximately 0.1 cubic feet of water which would translate to about 12 cubic feet of oxygen at 1,800 PSI.

I received a response from Bill McGowan at Zodiac Aerospace:
The cylinder in question holds 11 cubic feet of oxygen at 1,800 PSI
The size "A" cylinders hold 4.25 cubic feet of oxygen at 1,800 PSI