I have not seen any comparison of same bullet velocity using pyrodex loose powder and using 777.I know their is a big difference in black powder and pyrodex in velocity with same bullet, but havent come any info on this situation.
If you're lucky enough to be on private land and can leave your stand up during the off season you can tie an old piece of cloth or something of the sort to your stand. I like to use an old camo bandana that I have. That way the deer get used to the movement and eventually don't bother even looking up when there is slight movement. This may just give you the time to draw your bow or raise your gun without being detected.