Joe,
As you are actually lightening the weight of the ejecta/payload by cutting off the petals, I would expect that you are also lowering the pressure being generated, all other factors being equal.
If your curiosity is great enough you might consider sending both loads for testing as long as its the same pressure gun being used for both loads. And keep in mind that pressure guns are like engine dyno's; no two of them read exactly the same even though they are supposedly measuring the same things, so you will get different numbers if you send one load to one place and the other to another or even the same load to two dif. places. You will need to send them to the same place to get meaningful comparative data for that reason and that's all you will get, good comparative data. Actual pressure numbers reported will likely not be absolutely accurate, but close enough and will not alter the findings. Just saying.
Happy New year(!) and we can hope for better bird populations come next fall than this past year has produced. Still time to get plenty of walking in before this season closes;-)
