[Unclenick]

The flash brightness is mainly about the aluminum content. CCI went to it (or, more of it) in their magnum primers in 1989 because that aluminum spark shower seemed to improve ignition of the spherical powders then in use, as did the high temperature from using a barium oxidizer.

The only technical difference between magnum and standard primers is that the magnum primers make a larger volume of gas. This is to establish adequate start pressure in large cases. It also helps in a more medium size case when there is extra space due to low loading density.

Via phone calls, CCI has verified their 450 SR Magnum primer and their #41 military sensitivity primer have the same amount of the same priming mix. The only difference is in the anvil used to produces the lower military spec sensitivity in the #41. Same for their 250 and #34 primers. So the #41 and #34 have magnum priming mix in magnum quantities.

The trick with better ignition has to do with flame temperature, spark shower temperature, and duration as well as pressurization of the case. You are limited in how well you can tell a primer is doing that by looking at the flame photos. This is for the same reason that just because a candle makes brighter light than a propane torch flame, does not mean it is hotter or more energetic. It just means it puts more energy into the visible light spectrum and that's just a portion of the total energy of the reaction.

You can get a primer to make magnum levels of gas different ways. You can just increase the total priming mix or you can increase some of the fuel chemicals without increasing the amount of sensitizer and thus get more gas at lower brissance and with lower peak temperature but with longer flame duration. What strategy works best is powder dependent. QuickLOAD's author, Hartmut Broemel, points out that going to a magnum primer occasionally actually lowers muzzle velocity. This is because of the variety of approaches to making the primer produce more gas.

What you want to look at in primer reviews are the muzzle velocities achieved (higher means the powder got burning faster due either to more or better tuned (for temperature and duration) primer energy), and muzzle velocity SD's with your powder. If your powder isn't listed, you need to test it for yourself. For a given primer, some powders produce the best accuracy (at least, at closer ranges) without producing the lowest MV SD's. But I don't believe I've ever seen an example of a primer that produced the lowest MV SD's with a particular powder not also producing the smallest groups with it once the charge weight and bullet seating depth were tweaked to a sweet spot while using that primer. So look at MV SD as an indicator of consistent ignition (smaller is better) when comparing primers in your gun.