An Uncompromising Training Tool Nothing improves performance like training, but centerfire ammunition is often prohibitively expensive.That concern is now alleviated by the SIG522. This full-size rifle handles like the centerfire SIG556®, but fires affordable .22LR rimfire ammo. It includes a metal receiver, folding and locking stock, Picatinny rail, and just as importantly, the SIG522 offers you affordability, with familiar handling, acccessory interchangeability and genuine SIG SAUER® quality. Available in 10 or 25 round models. – Reliable blowback operation – Economical .22LR ammunition – Integrated M1913 Picatinny receiver rail for mounting optics – 7075-T6 Aircraft grade aluminum upper receiver with hard coat anodize finish – Lightweight polymer lower.