WRSI helmets come with a bunch of padded shims. I was right in between the two sizes, so I got a med/large and shimmed it up nicely. WRSI are great helmets, mine has taken multiple impacts and is still as good as new.
Most adults with a normal to large head use the bigger size. The smaller size is meant to fit people with very small heads, including children. I have a slightly smaller than average circumference head, and the large size was the correct choice. I used the thickest padding on the sides and front, and thinner padding on the top to make room for a skull cap. Fits like a dream.
Hmm. I wear a size 7 (ballcap - new era? on field hats), so I have a smaller than average cabeza. If you (airborne) are wearing 7 1/4 and have the thickest shims in the helmet...I'm not sure what to get. Thin pads in the small/medium?