Rifle primers use a harder cup than pistol primers and may not function when struck by a pistol firing pin. They generally have more priming compound and, thus, will raise pressure. Rifle primers, also, are of a different depth/height than pistol primers, about 0.008" taller. They will seat in the primer pocket but may protrude enough to prevent a revolver cylinder from turning or possibly cause a slamfire in an automatic (less likely, but possible).
I was loading up a batch of mixed brass for the 500 S&W some time ago. As it turned out, some of the brass had primer pockets for large pistol primers and some were for large rifle primers. I was using large rifle - loaded them all. The one that were "cross-primed" would not allow the cylinder to turn. Realizing the problem, I had to dismantle the cartridges.
Info from
http://www.exteriorballistics.com/re...ics/primer.cfm
The two predominate sizes of primers in use today fall into the basic categories of “small” and “large.” These may be further defined as being either rifle or pistol primers. Differences between the two include priming composition mixture, cup thickness and sensitivity, and very slight dimensional discrepancies in height. Within these sub-categories, the primers are defined still further, as standard, magnum, and in rifles, benchrest primers. Distinctions between these types vary from brand to brand, but most relate to composition mixtures, intensity and quality control standards during production. Diameters of the two sizes are .175" for the small rifle and pistol, and .210" for the large rifle and pistol, respectively. With so many different sizes and types available, how does the reloader know which type is appropriate for a given application? The following paragraphs will serve as a general guide for primer selection. In addition, the specific size, brand and type of primer used in our data development is listed under the Test Components heading for each cartridge in this manual.
Pete