Jake bring it up the camp during the early ML season and I'll bring up some of my handloads both 139 gr and 154 gr and see how it shoots them. We can set up a table and chair and get close to 100 yards.
My grandson has a Savage 16 and I have a Browning Micro Hunter - both in 7-08. His shoots the 154 gr best but and mine likes the 139s.
About your shotgun...I played with various slugs with an open sighted 87 smooth bore and it shot the Federal Tru Ball the best.