Re: Schmidt & Bender Parallax vs. Non-Parallax
The 12X scope with parallax set for 300 will work well at long range. There is very little adjustment between 300 and infinity on S&B scopes; the amount of parallax error will be small.
The problem will be load development at 100yds. That will be a PITA as shooting small groups will be difficult. Do load development at 300 yds and be happy. I'd use the scope without hesitation.