No, this is for a 308 caliber fn scar. This won't fit your Ruger 57. Sorry but hope this helps.

Kiionte, no this won't work with the Ruger 57.

Kiionte, no, this is for .308 Rifle Caliber. Cheers and stay safe! Ruger 5.7 Magazine Extension (+10rds) here : https://magsupplyusa.com/ruger-57-magazine-extension/

No, this is meant for the SCAR rifle chambered in .308. I don't believe a higher capacity magazine than 30 rounds from FN, Ruger, or Promag for the Ruger 57 or FN Five seveN.