I wonder if a magnum primer would affect the performance of a round much.  I have used magnum primers on my black powder revolvers and haven't noticed a difference.  The reason for asking is that often internet suppliers are out of small pistol primers, but they have an abundance of magnum primers (small pistol size).  With money getting more scarce along with gun parts and supplies (at least after Jan 20, 09, I'm looking for short cuts.  Are these dangerous shortcuts?  Thanks for the info.

Dave       

Magnum primers do have more punch that standard primers, so they can increase pressures to unsafe levels. I use magnum primers all the time, but only when the load manual calls for it.  Generally, thats for igniting ball powders or slower burning powders. 

Some primer maniufacturers don't make magnum primers. I read on the internet (so take it for what its worth) that Speer made magnum primers because they found their standard primers were not strong enough to reliably ignite their ball powders (like H335.)  So, rather that increase the power of their standard primers, they made magnum versions.  Other primer mfgrs, like Winchester, have only one primer that is strong enough to light any powder.

Changing primers can change the pressure of any load, so always stick with the primers that are recommended, or with loads that you work up.

Not reccomended, but they can work IF you aren't at the top of the chart and work up the loads carefully.  They can cause erratic velocities with some powders.

I interchange them all the time with the rifle brass, but then again, I rarely load to max powder charge... and yes, either way you load them, whether it be rifle or pistol, the magnums will increase pressure approaching max SAAMI.  My recommendation would be to either only use them when your reloading data recommends them, or only use them for slow burning powder.   

Does it matter or make a difference?  Maybe, depending on the situation.  Here are two data points from my little science experiment I just did with 223 (using BL-C(2) powder) and with 30 Carbine using W296 powder.  Magnum SR primers did make a measureable difference with the 223, but not with 30 Carbine.  This isn't a rigourous experiement because I'm comparing Winchester SR to CCI Magnum SR primers, and I already believe there can be measureable differences between ostensibly the same kind of primers (small rifle, say) made by two different manufacturers.  But, since this experiement was based on seeing a couple packs of CCI Magnum SR primers at the local Gander Mountain when I happened to be in there, that's whatja get.

223, 55FMJ and 27.5 grains (published max) BL-C(2) in Bushmaster XM15 with 1/9 16" barrel, col 2.215":
WinSR primers              --> 2815 +- 53 fps (sorry for the high SD, this is just 5 in a row).
CCI#450 mag SR primers --> 2895 +- 25 fps

Thus, these CCI magnum SR primers gave the same load about another 80 fps of umph.  I would qualify this observation with the note that I have seen slightly better group sizes when I was using standard CCI SR primers in my 223 loads than with the Winchester SR.  However, I was using CCI standard SR primers back before I had a chronograph, and so I can't say if there really was a difference in muzzle velocity or consistency (sd) with CCI primers vs Winchester.  When I finish using up all the Winchester SR primers I have I will probably restock with CCIs, it's just that they were out of CCIs the last time I made a stock up order.

30 M1 Carbine, 110 FMJ and 14.5 grains of W296, about 1/2 grain under the published max if I recall correctly
WinSR primers              --> 1937 +- 6 fps
CCI#450 mag SR primers --> 1940+- 17 fps

No significant difference in this cartridge using W296.