so far i've been playing my 50 cal. at pretty low levels, and to get a heavy distortion sound i've got to jack the gain knob to 9 or 10, with the master and lead master both around 1.5-2

is it typical that if the gain needs to be at 9-10 at low volumes, that as i turn the amp up louder i'll have to keep the gain knob jacked? and is it typical of amps to need the gain knob cranked this high?
no. You'll get more distortion the more you drive your power tubes. A lot of people don't realize that a lot of the size of the sound of an amp comes from sheer volume, not from jacking the gain. But yeah, you'll find yourself turning the gain down as you turn the volume up. Some Boogies also have push-pull knobs that are for low-volume use, but are unnecessary at higher volumes.
Hi, I'm Peter
not sure what your amp has but for main i usually crank the pre gain for good distortion and use the post gain for how much volume i want
Gibson SG's Rock
You obviously own a Peavey. Mesa Boogies don't work that way. A .50 Caliber is a type of Mesa Boogie combo amp. Does your Boogie have both a gain and drive control?
Hi, I'm Peter
yeah, i have my gain cranked at low volumes. As you turn it up natural gain starts to kick in and you suddenly don't need that much dist. Your sound gets muddy and washy when there's a jacked gain knob at high levels on most of them "metal" amps. I'm talkin about tube and valve heads ofcourse. So yeah, more vol. means less gain in the sense of a good guitar tone.