SchoolBoy: Back once upon a time magnum primers were the suggested and go-to primer for 2400 powder for loading 357, 41, and 44 Mags. I loaded hundreds of 357 ammo using 2400 and hard cast lead, cast lead bullets with gas checks, and JHP's using 13-15 grains of 2400. Real ear splitters, fire breathing, hard hittin cartridges. Now, due to a change in the formula of 2400, most loads for 2400 call for standard small or large primers, depending on the caliber. Standard primers are all I use now for 357 and 44 Special and 44 Mag loadings, with a few exceptions. Unique will only need standard primers. You need to consider the burn rate of the powder as to which primer you need. If you are going just to shoot at a standard range or in some gravel pit somewhere, the 1200-1400 fps 44 mags are of no consequence-your choice. But CAS rules limit your firearm power range to somewhere less than 1000 and no jacketed bullets. Someone that is 'up' on the rules will have to chime in on this, but I do know their are restrictions. See you posted while I was typing this--take the items back and get a refund or what you need if in stock.
Hate saying this, but I've found over the years some of the 'sales people' at places like Cabela's, Bass Pro, Gander Mt, and such---well sometimes their experience and knowledge comes from what they were told by someone, who sometimes isn't real up on all the real needed knowledge on firearms and reloading or they read a "Fast Reloading Guide". I don't know how many times I was fed some line of BS, sometimes holding my tongue, other telling the 'good intending' sales person what really was. Heck, some of my guns are older than some of the guys wearing slacks and a tie. Not saying in all circumstances. Just saying to be careful of what you are being sold, just to make a sale. Helped one would be component shooter/buyer in a gun shop one time who came in to buy powder/primers for his newly purchased AR-15 5.56. He had sat in a session with a relative loading some ammo, came to buy some for himself and was going to buy some rifle powder geared for heavy 30 caliber loadings. Asked me for advice and when I showed him what he should have, his response was "Well all powders are the same aren't they, doesn't make much difference". Gave him some free/safe advice. Just sayin-if ya can't find what you need or want, don't just buy anything so ya can start crankin out ammo and use a lot of desecration when being told by some employee at a retail store. Most will give you good advice, but there are those who don't have the expertise to be in in the firearm department, maybe should be selling Nike tenny's.