Newbie question but here it goes - I just picked up the 10FCP in .308. I keep seeing references to the 10FCP-K and don't see the difference. Mine has the accustock and accutrigger w/muzzle brake and fluted barrel. Can you explain the "K"?

Also looking for higher capacity magazines. Please provide the link to the SSS mag site mentioned. Have done searches with no luck. Thanks.