BackCountry cross-slot bases are machined from 7075-T6 aircraft-grade aluminum for lightweight, rugged performance. Fits both Picatinny and Weaver-style rings. This model will fit a Winchester XPR Long Action with 20 MOA.BackCountry cross-slot bases are machined from 7075-T6 aircraft-grade aluminum for lightweight, rugged performance. Fits both picatinny and weaver-style rings. Available with zero elevation or 20-MOA for long-range shooting. Features: These 1-piece bases feature a 20 MOA slope for long range shooting applications