Help with shot count and refill bottle

[shrive81]

Hey guys,

so getting a new setup together for PCP shooting and going to have the FX M4 with the 580cc bottle. I have few 45minute SCBA bottles that i can use for filling was just wondering how much shooting "roughly" you are getting out of a gun with one SCBA bottle at the field. When i use the calculator if i use a 300bar bottle on the gun it says it will only fill it 1 time at 150 bar. Just wondering how much shooting i can plan in getting...


Thanks in advance this is a whole new world for me and appreciate the help

 

[jland48]

Hey guys,

so getting a new setup together for PCP shooting and going to have the FX M4 with the 580cc bottle. I have few 45minute SCBA bottles that i can use for filling was just wondering how much shooting "roughly" you are getting out of a gun with one SCBA bottle at the field. When i use the calculator if i use a 300bar bottle on the gun it says it will only fill it 1 time at 150 bar. Just wondering how much shooting i can plan in getting...


Thanks in advance this is a whole new world for me and appreciate the help

Most PCP guns require more air to shoot continuously than you will be able to supply with your bottles. I would suggest you get a compressor for this. Something like a GX-cs3 would work well and is fairly inexpensive.

 

[AlanMcD]

Calculators don't work too well when the fill level is basically at the same level as the full tank. You get very few (if any) full fills from the tank, and then you get ever decreasing partial fills when you top off . . .

I prefer to look at it another way: when you connect the tanks for a fill, you have a 580cc tank at lower pressure connected to a ~6800cc tank (your 45 minute SCBA) at higher pressure for a total system volume of 7380ccs of air to balance out when the valve opens. And the big tank is 11.7 times the volume of the little tank. You'll need to identify the equation that leads to equalized pressure, and then solve for the variable to figure out the pressure the system will equalize at when the fill is done. It looks like this:

Pressure in big tank minus "X" = pressure in gun's tank plus 11.7 x "X",

Thus "X" = (starting pressure in big tank - starting pressure in little tank) / 12.7

Then plug the value of X back into the equation and you'll see what the fill level will be when done - and of course this would have to be done for each new fill. For example, lets assume the SCBA tank is at 300 bar and the gun's tank is at 150 bar when you go for a refill, and you want to refill as high as you can:
X = (300-150)/12.7 = 11.8, and then
Ending pressure of the system would be 300-11.8x1= 288 bar for the SCBA (and of course 150-11.8*11.7=288 bar for the gun's tank).

You'll lose a bit of air when you vent, but your start point for the next fill is about 288 bar. You can repeat this to see how far you think it would be worth while to keep filling . . . . (spoiler alert - the next fill will get you to ~277 bar, then about ~267 on the one after that)

You can use any pressure unit you want for this but you have to be consistent through the whole calculation - the value for "X" will be different under different units, and thus you can't mix them.

Hope that helps.

 

[Peashooter]

I use to be able to shoot a whole month on a 300 BAR 12 Liter dive bottle, and firering quite a few .177 shots in the process, already back then 1000 shots in a day at the range was no problem.
Shooting tethered also mean i shoot my bottles lower, CUZ using like 80 - 90 BAR regulated pressure to shoot with i can shoot my main bottle down to 150 BAR or less.

If you are filling your rifle bottle and then disconnecting, you ideally want to fill it to the max pressure to have your ideal / MAX shot count, and so i assume you will be prompted to fill your main bottle at a higher pressure, which by no means is a problem if you have your own compressor, but going to some shop to get it done is a buzz kill, or it was for me.
Also dive shops here dont really want to touch 300 BAR bottles.

I now generally use a 9 Liter carbon fiber bottle, CUZ my steel / carbon bottle are too damn heavy to lug around.
But i also have my own compressor to fill my tanks now.

If you are shooting a .30 rifle,,,,, well you will be using a lot more air than i am.

Spoiler i can shoot with like 40 - 50 BAR pressure and still get my .177 pellets up to their ideal marching speed, a 700 mm long barrel help with that.