Just got a new MPA 300 Norma Mag today, and did what I've done several times in the past ... I picked up the phone and called Eric at Possum Hollow. He answered on the second ring, took the action and caliber info, asked a couple of good questions, and figured out exactly the bore guide I needed to fit the action in my new rifle. He didn't have any in stock, but told me he'd "make me one" later today and get it shipped out tomorrow. If you're buying bore guides online hoping to get the right one, or if you're not using a bore guide sized specifically for your action ... then you might want to rethink your strategy. Here's his contact info ...