They are harder, I use them in my really hot .357 loads because they don't flatten out as much and don't jam up my Green Machine at the size/de-prime station
The only difference in primer size is the large pistol and large rifle. The cup size on the small rifle and small pistol primers are the same size. The cup is harder normally on the rifle primer to withstand the higher pressures and account for the lighter strike on the primer in handguns. Rifle primers do have a somewhat higher energy flash than pistol primers, and of all the brands I have researched, the Federal have the hottest primer out there. If you load is at or near maximum, you might drop back a little and work back up watching for pressure increases. The only reliable way for the home loader to do this is with a chronograph, looking at velocities and comparing them to published data. I have looked at primer flattening, measured the web area of the case before and after firing and while it was in interesting experiment, it didn't completely track with the velocity measurements. I find that the chronograph is the main tool I use in load development. Good luck with the experiments.
Like others have said, reduce you powder and work up again. This can cause other issues. Since the rifle primer is harder it can take more pressure to show signs of pressure (flat primer). You can actually load a little hotter with the rifle primer because it is harder and doesn't pierce as easy. The other issue because they are "harder" they won't seal as well in the case when fired. This over time will cause flame cutting on your bolt face. This usually take several thousand rounds, but back in the day loading 9X21 to major power factors you had to run 'em a little hot. Saw this in several race guns including mine.
Will they work? Yes. Just work up to them.
Will they work? Yes. Just work up to them.
