I use foster slugs in my Savage 220F just for trigger time in spring and summer. It's a pain to clean before deer season but the cost difference makes up for it.
I would not use foster slugs to even get on paper as you will have to unfoul your rifling before using sabots. Use the rounds you're going to hunt with. Start at 25 yds and work your way out to 100, adjusting as you go. I shoot Hornady SSTs 3" high at 100 and dead on at 150, 6-8" low at 200.
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