Obviously you're aiming to catch the bounces in flight vs. examining evidence of a bounce post shot.
I'd start with the later.
In a good setup my bet is 2 bounces...first right after the hopup nub...the second close afterwards and then I'm guessing it's stabilized and/or doesn't get a third bounce before it's gone from the barrel.
You could cheat and coat the inner surface of the barrel with a thin flim (say Molybendum)...then shoot a bunch of shots and look for discolouration patterns (it'll turn more silver as it's impacted). You could also capture BB's after the shot and if they had black marks on them then they've hit the barrel somewhere.
You don't even need a clear barrel to see that...just don't get any on your hopup rubber. I'd see coating the entire barrel...then cleaning the first inch of it (or just past the hopup cutout)...then assemble, clamp you gun in a vise and shoot. You can get powdered Moly at shooting places.
I'd stay simple and just setup for one set of tests....one standard barrel length (say 363mm) with 0.20's @ 350fps. Detail and publish the test setup and results and put it out there for peer review. Filter through the reviews and adjust testing from there.
Best of luck with this.