Sticking with the "most accurate" load is always a good idea, but you might be using a lot more powder than you feel is really necessary. But you also read about the danger of cutting things back too far and the ball/bullet could "bounce" off of a hard surface. Just like a BB gun when you were a kid... and we all know how hard those BB's can hit, even though you see it coming back at you it's hard to get out of the way. OUCH!
Forget velocity if you don't have a chronograph. It doesn't mean as much as the results do in the woods (or field). What you want is a load that will just punch through a 1 x 4 board (which is 3/4" thick) at a range of about 100ft, and that will also prevent the "bouncing ball" problem.
At that 33yd range, if your gun can't group better than about 1 1/2", then you're going to miss a lot of squirrels' heads. There is what I do with using a large bore for squirrels--now as far as the actual powder charge?--you'll have to try and work the load up (or down) to produce those results. If the typical distance that you get shots at squirrels is longer or shorter, then use "that distance" for your test groups and board penetration.
It's still a whole lot easier to use a .32 or .36 cal BP gun for the squirrels, but if you have a .50 that's accurate, there's no problem with doing that--'cept you'll use more powder and lead to get the same job done. It's still a whole lot of fun to use what you have, and you also get that extra practice in with your big game muzzleloader too.
Good luck and have fun!
WV_Hillbilly