I said assuming I guessed correctly, which would be around 50% of the time. Add on top of that, I personally was a piss-poor marksman, so take away 2/3rds to 3/4ths for me screwing up the lead. Also, you're assuming I had a guns solution, saw all of them, and ample time to react on 13 targets.
In the K4, how many kills I LANDED varied greatly. I'd have some sorties with 8+ kills, others I would land just assists, and others I would die without having had a guns solution.
Also, the way I was taught the K4 meant that when I got to businesses, there were far more crossing shots than 6 o'clock or low angle deflection shots. Bear in mind that most aircraft have wingspans in the 30+ foot range, and the MK 108 acts almost like a shotgun at times.
I was just surprised the guns had that much dispersion, although actually thinking on it and comparing it to in game observations, its about right.