cannot say about magnum primers, however I once, due to lack of attention, loaded a bunch of 45ACP with Winchester Large Rifle Primers (Winchester primers were supposedly "hotter" than other brands). My load was 5.2 grains Red Dot with 200 grain SWC (900 ft/sec). To make a long story short, experienced NO problem. Since making that one mistake, I pay more attention to what I'm doing.
They say that "god looks after drunks and fools", but it's best NOT to strain the quality of mercy. The load you mention sounds like it's a lot less than max.