I have been having problems just like the rest of you finding small rifle primers. I have a lot 5000 of the small pistol primers and thought that I would see if anyone else has tried it.
So your a wildcatter! lol I wouldn't risk it. The pistol cups are softer as has been said. You may get away with it once or twice, but 3 times might be the charm! I have alot of reloading experience but I don't know everything and I'm not a Wildcatter. I would go here to ask your question. These guys will know for sure and if it can be done, someone on Accurate Reloading has done it!
The difference between Small Pistol Primers and Small Rifle Primers is the thickness of the bottom of the Primer Cup to contain the pressure of the round being shot. Pistol Primers have a thinner primer cup than Small Rifle primers. Rifle cartridges have more pressure built up in them during ignition than a pistol cartridge other than a couple of exotics loaded to IPSC major like 38 Super and some hot 9MM major loads which are really wild to load and shoot. Use small pistol in pistol calibers and small rifle in rifle calibers. The small rifle calibers ignite hotter than the small pistol primers also which can cause issues if used in a handgun round. The issue with small pistol used in a rifle load is that if the primer cup blows you get some of the pressure in the gun bolt and maybe your face!
It depends, normally you don't want to deviate to much from reputable data or components. That out of the way, I have tested small pistol primers with modest 204 Ruger loads fired in a bolt gun. I observed no adverse issues.
Now if you plan max charges in your AR, I'd have to say NO.
If your gun can not slam fire and if you keep pressure to 35ksi and less, it would "probably" work--though the striker might pierce the primer.
Small pistol magnum still have softer/thinner cups than rifle.
Things are tough all over, but a blown rifle will really set your day back.
Small rifle in a pistol will often not ignite without multiple strikes--the main spring is just too weak. If you up the mainspring, you will, generally, up the trigger weight.
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