The total capacity should be 9-10. The rounds end up with the case head into the notch in the rear of the magazine yielding even greater OALs.
I've shot more that a few coyotes with the 75 AMAX from 16" AR with a MV of ~ 2500. They were all less than 300. More like 250 or less. It killed them dead just fine. They are not explosive on prairie dogs like the VMAX, but they all died too. The most amazing thing was shooting them at mag length with a HEAVY compressed charge of Varget and the bullets took a HUGE jump just fine. When the planets are aligned, that little rifle shoots 1/3 MOA groups with that load.
If you look carefully at Steve's mag, the two pieces are clamshelled together different than most, making it easier for OAL modification.