As far as taking a shoulder blade shot and breaking the deer down, I see no problem with the bullet and powder charge you're using to get the job done. Poster Omega showed that moose shoulder blade broken by the same bullet and a little more powder. I am sure what you have loaded would blow that out without a problem.

Another shot I like is when they quarter to tuck it behind one shoulder through the vitals and into the off shoulder. Many times that will knock them off their feet also.

Neck shots at long distances are risky and especially with a muzzleloader, and spine shots are tuff to judge on a big buck. I think what you're planning will work fine.