Took me quite a few reads to actually get what you're doing to test the length of the vehicle. I had to laugh a bit to be honest, it looks like the poor man's equivalent to analyse the velocity by analyzing frames in a video. At the same time it is super creative.
Anyway, the way I thought about this initially was closer to your second suggestion. Basically count how many shots have missed and how many hit with a modified unit (0 accuracy, 0 horizontal scatter, no impact etc). Based on the scatter angle and the ratio of hit shots, you should be able to estimate the length. Are you really sure you need so many repetitions? By gut feeling I would have assumed that probably 100 would already be at least okay, although I have not tried to estimate this with a calculation.
However, I had a second idea:
We could take a bunch of standardized vehicles (0 accuracy etc as above...) that just differ in their scatter angle. Each will then shoot at a target at fixed distance. If the scatter angle is too small, all shots will hit. If it is too large, there will be misses. At range 40, each 1° increment in the scatter stat would correspond to 0,35m in vehicle width. So depending on how the angle increments are set up, it would probably be possible to nail the width down by 0,2-0,3 meters.
On the other hand, I think your second method is probably more straight forward. I'd just take less shots, should be good enough. Especially if you can cross check with similarly sized units. If the test gives you similar results for the P4 and T34, I wouldn't worry too much about it.
As to the ROF being a bit off for some units, I used an old formula to calculate the average time between shots that might be somewhat inaccurate, especially in light of what you dug up recently in your ROF thread. I don't think the deviation is too great (maybe a frame more or less here and there), but I'll probably try to update this in a future release...
Or are you specifically talking about the delays in the 'Head-to-head' tab? These are randomized between the theoretical min and max values on purpose to give the sim a more realistic 'feel'.
Yes, I was mostly asking about the head-to-head tab. If you'd have taken the average reload time, it could make the difference between consistently shooting 0,1 seconds earlier than the opponent which would lead to a clear victory. The randomization doesn't solve this, but at least will give some more realistic picture of the real variance.