As to shot in a rifled barrel, it does not work well with the modern faster twist rifles but you could be surprised. When we get to the 1-48 inch twists and slower in a BP rilfe it may not be so pronounced. Straight rifling has been used in shotguns. Shot could cause leading. A 50 is a 32 gauge and would likely work with up to about 60 grains of powder/same measure shot. I would not expect to pick running squirrels out of treetops with it but it might work up close. Squirrels can be barked but it is as easy to head shoot one. I tried it once and the squirrel jumped up in the air and called me everything he could think of in squirrel chatter and ran off before I could reload. I thought the situation so humorous my speed loading was slightly impaired. You can use toilet paper, paper towels, wasps nest or whatever for wadding. Sounds like you need a fowler.
DP