"...what bullet weight..." Don't like quoting Wikipedia, but they claim: "The rear tangent sight was graduated for 1893 pattern 7×57mm Mauser cartridges loaded with a 11.2-gram (172.8 gr) long round-nosed bullet from 400 to 2,000 m (437 to 2,187 yd) in 100 m (109 yd) increments."
Prvi loads a 173 grain SP. I'd be loading or using a 139/140 though. Just for the lighter felt recoil.