I think it depends on the cartridge. .223/5.56 and .300 BO use normal AR mags. I think 350 Legend does, too. 7.62x39 uses Mini-30 magazines. Some of the others use AICS magazines.
Hopefully, the gen II's will eschew Ruger's proprietary magazine.
https://shopruger.com/Magazines/products/2151/
https://shopruger.com/Ruger-American...uctinfo/90747/
https://shopruger.com/Ruger-American...uctinfo/90746/