Doing some initial shopping at MIDWAY USA and notice that they classify their handgun primers by "large pistol" and "small pistol". I was surprised to find, when reading reviews about the small primers, that some said they used them in .45 ACP. That lead me to believe that the difference between "large" and "small" was not about the caliber of gun.

Would someone please educate me on this?

By the way, in the "large" category, they have none on hand are are not backordering. In the "small" category they have these http://www.midwayusa.com/viewProduct/?productNumber=568829in stock for $30.00 per 1000. They seem to get good reviews so that is what I'll order, but I'm still curious about the large and small issue.

Thanks,
Craig