New to ARs here. I ordered a Seekins SP-10 in 6.5 CM yesterday. I believe it comes with a 20 round magazine. I want a magazine that will permit shooting from a bench without protruding lower than the grip. I understand the rim of 6.5 CM is same as 308 so the mags are the same? Will a 10 round PMAG work with no feeding issues? I attached a picture of one to be specific. Thanks in advance.