Open Question: How many PSI of propane to achieve 103mL of it?

I'm working on my spud gun and adding a fuel meter to get consistent firing. Given various numbers (fuel ratio, chamber size, etc) I need 103mL of propane for an ideal firing. The volume of the meter is about 125mL with a basic PSI gauge on it. What pressure should I be shooting for to get that amount of propane that I need?

Also, if you're into this and know of a good fuel:air ratio for propane, feel free to share. I'm using 4.2% by volume for my calculations.

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