A
substantial amount for
self defense?

With a pistol?
I think most self defense situations are over in a few rounds, a few mags at the most. When the smoke clears from your self defense situation, the police will just confiscate the rest of your substantial amount of ammo regardless.
If you have a situation where you need a
substantial amount of ammo, perhaps some other firearm might be better suited.
Could be that I completely mis-understand your definition of substantial....