Accuracy wouldn't exactly be the purpose of them, that'd be the DMR's job. If you'd prefer I could go with another primary weapon instead of the second SMG, maybe the [url=http://halo.wikia.com/wiki/M319_Individual_Grenade_Launcher]M319 Grenade Launcher[/url]? If not I'll just go with the Magnum like you.

EDIT: Two ideas I'm currently toying with would increase the effectiveness of the SMG'S however.