I tried watching that dude's videos on youtube. In my opinion, it is dangerous for him to even be posting his advice on youtube when it could damn well get someone killed. During his reloading tutorial, he actually switched to priming a 223 case becasue he did not have any primers for the 9mm case he originally started with. Believe me, you don't want his advice and you will see partially why. To answer your question though, when it comes to small rifle vs. small pistol primers, there are only two differences. Brisance and hardness. Brisance is a measure of the explosiveness of the primer. Hardness determines how much force is needed to ignite the primer. Since these two primers are dimensionally the same, they can safely be used interchangeably in some instances as long as caution is used. Rifle primers have more brisance and hardness than pistol primers. Magnum pistol primers are somewhere in the middle of both and can be a viable compromise. I’ll keep the discussion on both ends to keep it simple though.

I would not suggest using pistol primers in semi-auto or automatic rifles to prevent slamfires. Since pistol powders burn a little cooler than rifle primers, be careful of delayed ignitions. This is when the firing pin strikes the primer, but there is a delay in how long it takes to ignite the powder. If you run into this problem, wait 30 seconds before taking your rifle off target or unloading the cartridge. This usually is not a problem if you stick to the faster burning powders commonly used for 223 with 55 grain or less bullets. Another problem to watch out for is the rifle puncturing the pistol primers, since they are softer.

I think the better route to go is to use standard small rifle primers in both, granted your pistol is able to ignite the harder primers. Glocks and other striker fired pistols might have trouble in this department (I’m sure you are familiar with this by now). It should not be a problem with a strong hammer fired pistol, such as a Browning Hi Power. Just make sure to work up your load using the rifle primer, as switching from a pistol primer to a rifle primer normally increases pressure because of the increase in brisance.

Unique is a good all purpose shotgun and pistol powder commonly used for 9mm, but can be used in some rifle cartridges with good results for reduced loads and plinking purposes. I have had great results using Unique in my Remington 799 with 40 gr V-Max and 55 gr FMJ bullets. If I can recall right, without digging up my notes, I was able to obtain velocities with the V-Max around 2700 fps with 2.5” groups as the norm. 55 gr bullets were closer to 2200 fps and accuracy was about the same. Great plinking rounds if that is your intentions. I keep more Unique at hand than any other powder. It is a powder that has great versatility. It might not be the best in some cases, like rifle loads, but it can be made to work when in a bind.