40 shots is good. Charge the Marauder Rifle with about 1-2 ounces at a time. Anymore and you will chance blowing out liquid CO2 (wasting).
They don't fill tanks with liquid CO2 all the way, for safety reasons, they have to allow for expansion and contraction at different temperatures (higher temperature = higher pressure).
CO2 is
more temperature sensitive when compared to air
http://www.weatherquestions.com/air_components.jpg or Nitrogen only. This can cause
Point Of Impact changes when shooting at different temperatures. Where your POI may be on at say a 60 degree day, the pellet will probably impact higher on a 90 degree day, and vice versa. Knowing that, you can then compensate by adding UP or DOWN clicks on your scope as needed, or by aiming a little higher or lower. Knowing how much comes with experience.
If you can find a used bulk tank, like some restaurants or convenience stores use, something like these:
http://www.micromatic.com/beer-question ... id-89.htmlyou can have them refilled at your local fire extinguisher shop for about $1.20 per pound. These tanks can be heavy, so try to find one locally to avoid shipping charges. These tanks can last a very long time before needing to be refilled.
Since CO2 is denser than air or nitrogen alone, you will need to open up your Valve Metering Screw (see owners manual
http://www.crosman.com/pdf/manuals/BP17 ... -%20OM.pdf) Remove the stock, then with a 5/64" hex wrench,
first remove the jam set screw by turning it
Counter Clockwise,
then turn the V.M.S. screw
Clockwise (be sure to count the number of turns so you can adjust back to the same setting later if you need to) until it stops, then turn the screw Counter Clockwise 4-1/2 turns, now the flow should be fully unrestricted.
I would also recommend making hammer stroke and hammer preload adjustments in order to prevent excess noise and waste of the CO2. If you don't have a chronograph, I would recommend a setting (remember to count the turns and make a note in case you want to return to the factory settings) of CCW until stops, on the Hammer Spring Preload (1/4") and 12 CW on the Hammer Stroke (1/8"). If you want to increase the velocity, adjust the Hammer Spring Preload CW 1/2 turn at a time but no more than 2 total. Again without the aid of a chronograph, you will have to decide what is acceptable.
Hope this helps