101combatvet,
It can happen. Back around 2005 or so I called CCI and the lady who answered the phone back then before the big conglomerate bought them assured me that a lot of their employees bought the CCI 400 and used it both for rifle and magnum handgun loads. She even looked on their database and told me the cups were the same and anvils were the same and the amount of priming mix (same mix used in both) was the same. Just different box labels.
Since then, the formulations have changed a little. If you call CCI today, they will tell you they are not the same and not to interchange them. The test Shadow9mm refers to is
this one. But that's in a pistol cartridge. In another video, the CCI rifle and magnum pistol primers are interchanged in a rifle, and the rifle primers produce more velocity. In
this video a rifle starts making loose primer pockets when the primer brand and type is changed.
A couple of comments related to the thread in general are in order:
According to Allan Jones, who worked on this stuff for CCI at one time, primer compositions and formulations change more often than people realize and the changes are not announced. Naturally, the primer maker want to avoid making past recipes obsolete, so the performance change is generally not dramatic, but there can be a bit, which is why we set out loads back and work up with a primer change) and check to see if we have to adjust our powder charge to hit a given velocity.
Pistols cartridges are not rifle cartridges. The powder space is small. One result is that more powerful primers can sometimes start unseating a bullet before the powder's pressure builds enough to do it, and this increases the powder's starting burn space. A magnum primer's primary function is to make a greater quantity of initiating gas than a standard primer does, and an ironic result that can sometimes be observed is a magnum primer can actually reduce velocity and pressure because of that effect. But is isn't guaranteed, so don't assume it will happen. Just assume you will have to reduce powder and work a load back up with a change in primer.
Don't extrapolate from what happens with one brand to another. CCI 550 and 400 primers may be fine in the 9 mm, but I would not assume from that I can do the same with other brands. There are several tests of primer effect on muzzle velocity you can find online. Sometimes it is what you'd expect, and sometimes it isn't. So always back down and work up.