For what?
You have a choice between Federal and Federal. Nobody else appears to make a magnum match primer.
In any case, magnum primers are about the powder used and the weather. They burn a bit hotter for a bit longer and are for lighting hard to ignite powders and for extreme cold weather shooting. You don't need 'em unless your manual says to use 'em.
Mind you, anybody who was out shooting in those -60 wind chills AB had a few weeks back is a sick puppy. The -40 the Queen's Service had me out camping in, long ago, was bad enough. Silly buggers gave us fresh rations too. Whacking a tomato with a pick axe handle didn't even mark the love fruit. Like hitting a friggin' rock.