- Leupold® Cross-Slot mounting systems feature Weaver-style rings that work with both Weaver or Picatinny rails with 1-piece and 2-piece bases available for many popular rifles. This model is designed to fit a Nosler M21 and is ideal for standard to magnum calibers. Our Cross-Slot mounts include the PRW2, QRW2, LRW, and Open Range series and deliver unmatched durability and strength. The PRW2 mounts are very popular since many rifles come with Weaver-style bases or cross-slot rails. QRW2s also work with cross-slot bases and offers the same features as our QR™ mounts, including +/- ¼ MOA accuracy when removing and replacing your optic.