The standards for F/Tr are Nightforce 8-32x and 12-42 BR. Others certainly use the NXS models, but they are heavier, and have 1/4 moa adjustment, as opposed to the 1/8's the BRs have. Sightron's new 10-50, and 8-32 models seem to be getting good reviews, but I havn't used them. There are still quite a few 8.5-25 Leupolds on the line as well. They are a good option if your rifle is on the heavy side and you need to come in under 18.2 lbs. I'm pretty sure I saw a used 8-32 NF BR in the EE for a decent price yesterday.