[SVD]

I'm getting the 7-10 hours suggested on a 20oz tank. I did have a tank give me shorter times and it turned out to have a loose safety valve - that little bit sticking out of the front. Once I tightened that up it was fine.

I went by a paintball shop and got the (apparently) standard refill kit for about $40. Had to go to the local welding supply shop for a 20lb tank. Initial cost was, IIRC $236. Refills on it are only about $20. By my math it'll have paid for itself in about 150 refills. Make sure you get a tank that has the dip tube to feed from the bottom (liquid rather than gas). Just tell them what you're doing and they'll make sure you get the right stuff. You also need a scale, btw.

Refills are pretty easy. Put on gloves and goggles. The gloves because venting CO2 can freeze your skin and the goggles so nothing gets blown into your eyes.

Hook your tank up to the refiller gadget, open the 'destination tank' valve on the refiller, hold the tank upside down and open the vent valve on the refiller. If this is the first time with this tank stop, unhook it, and weight it to get the empty weight (the 'tare'), then hook it back up.

Close the vent valve, lay the tank on the scale and either zero out to the weight of the tank + hose or just note the current weight and your 'destination' weight. Gov't recommendations are to underfill by 10% which means no more than 18oz in a 20oz tank or 21oz in your 24oz tank.

Open the valve on the source tank - if your forgot to close the vent valve you'll notice that right away. Watch the weight on your tank as it fills. I only seem to get about 16oz to go in with the way I've got stuff set up but since it's no big deal to refill it's not worth fighting it. When the tank is full / at weight you turn off the source tank valve, the destination tank valve, and then open the vent valve (to vent the pressure in the line). Once the line is clear you can unhook your newly refilled tank and weight it to confirm the fill (that's why you need the empty weight recorded). Whole process takes me less than 10 minutes and I'm still new at it. Keep track of how many fills you've done so you know when your big tank is getting low.

Here in KC it's $4 and a drive to get a tank refilled by someone else. Doing it myself is about $3 so the savings on the CO2 will - eventually - pay for the tank and refill kit. Not having to go anywhere on someone else's schedule - priceless. (OK, I do have to use my lunch hour from the day job to get the big tank refilled but that's actually less bother than taking the small tank to either place near me.)