Good point: power output has a disproportionate effect on air consumption.
A larger loss of efficiency is likely if the gun has been badly tuned. When the reg was fitted, do you know what other changes were made? If not, can you find out?
As
@sagalout says, sight of chrono readings (MV) for a full string can tell us a lot. Ideally you would need to keep a note of cylinder/bottle pressure as the string progresses. You can take a short cut by interspersing short strings with dry firing, but that won't enable us to assess air consumption. Ideally, to measure air consumption accurately, you need to fit a digital gauge on the gun... well worth investing in one (cheap Chinese will do) if you intend DIY tuning.
Once we see a string we might start asking questions about what parts have been changed/modified.
