I have several 5 round mags for my M1-A. One of them fits flush with the stock, but I has no markings on it. Think I traded a 5 round AR mag for it.
I have a Vltor Modstock which I love. Ordered it from SKD Tactical. Great customer service
http://www.skdtac.com/Vltor_M14_M1A_..._p/vlt.204.htm