" Are they most common in 99H?"
I've collected data on every 99-H that I could read a serial number on over the last several years (229, so far) and the calibers are as follows:
30-30 = 50% 20 years
303 = 35% 20 years
250 = 10% 8 years
300 = 5% 2 years
PS...anyone who has added one to their collection please let me know. I would like to add the details to my list.