Your Browser is Outdated
Since this is tagged as fitting the AR-15 based 57X28 it will most likely NOT fit the Ruger 57 handgun. The AR version would mean the CMMG AR-57 Magwell fed AR-15 conversion which has proprietary magazines which means these drum mags will be limited to that firearm. It is cheaper to just buy more of the metal OEM and aftermarket Ruger 57 20 round mags and roll with it.
It appearsthat, by listing description and information, that these will only fit the CMMG Converted AR-15 chambered in 5.7X28 due to the proprietary magazine required by that caliber conversion. You can review the barrel and BCG kits for the AR-15 and compare the information provided at these sites to verify fitment since these drum magazines are relatively new to the market and feed from the bottom using the standard AR magwell where the actual AR-57 57x28 uses P90/PS90 top feeding magazines and eject out of the AR-15 Lower receiver magwell. I have one of the 16" AR-57 top feed carbines and the 50 round OEM and aftermarket mags work very well in it. Took a bit getting used to ejection out of the magwell but adding a gutted and trimmed lip mag to it makes for a great brass catcher to save spent rounds for reloading later.