Don't understand why this particular forum, of all the different gun forums I visit seems to have such a chip on it's shoulder in the "Handloading" area. I've also seen that I'm not the only one who has noticed this.
With that in mind -- don't read my post.
If you -DO- elect to read my post, do so at your own peril.
If you have read this far, also plan some patience if/when you demand citations and proof of anything I elect to say. As in, it won't be forthcoming but you may feel free to demand and wait for it.
A contact at CCI has divulged on at least one occasion that the CCI-400 small rifle and the CCI-550 small pistol magnum are the same primer in two different packages. I myself have used the CCI-400 with fantastic success in .38 HBWC loads powered by Bullseye across six different Model 52 pistols, it's all that I load in them. You can use them anywhere a small pistol primer is used as long as you have the ability to reliably detonate them. My 52's do, my five different tuned PPC revolvers however do not.
Some folks have found that 2400 happens to be a powder where standard primers have offered better accuracy than magnum primers -- possibly a bummer for the folks who use Winchester small pistol primers that are marked "for regular or magnum loads"
These experiences are my own, I hope that sharing them helps.