The man i got them from said .308 but didnt know what other than NOT an AR10. The mag will easily hold a 30 06 . I have been lookinh but can't seembto find a solid lead. The Made in USA stamp looks familiar but if i remember it was not a high quality mag i saw it on. It is a big mag with a 7/8" wide and 3 3/8" long. Long shot but maybe someone has had one before. Thanks, Danny