As far as the ammo:
I usually only buy ammo in bulk except for hunting ammunition.
https://ammoseek.com/ is the
best place (search engine) that I know of for
in stock bulk ammo.
And the shooting:
Learn about the specifics of your firearm. That includes the steps to the function and how the
different parts contribute to malfunctions.
Practice, using snap caps, used casings, and dummy rounds, how to clear malfunctions. Conduct
magazine change drills and dry fire draws.
Dry fire the hell out of your weapon. Modern weapons don't tend to have issues with dry firing.
Consult your owner's manual for details though.
Go to the range and practice in stages. Practice grouping your weapon at the range you zero at.
Then zero the weapon and confirm the zero.
Practice multiple target engagement. Then practice live fire target engagement with magazine
changes.
When you are comfortable try practicing what we call reflexive fire. This includes engaging
targets to the left and right, and focus on transitioning your body to the appropriate direction.
Practice moving and shooting.
Start with dry fire, then move to live fire only after you can comfortably and safely succeed on
dry fire.
Practice starting in different positions such as sitting down, being behind a barricade, and reacting
to situations where you are trying to defend yourself, such as in your car (dry fire only) and in your
house (dry fire only).
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Remember, expertise does not come from special training. It comes from the basics. Practice the
basics until they are second nature.
But, I'd recommend you to sign up and take at least a basic pistol class at a local training facility
as a refresher. Always good to sharpen skills that become a bit dull. It might be a bit pricey, but
it's well worth it. Then practice, practice and practice some more.
"Owning a piano does not make one a pianist any more than owning a handgun makes one
a good shooter.
" - Jeff Cooper, founder of Gunsite
It's always been nice having his world class training facility right in my backyard:
https://www.gunsite.com/
Plenty to be learned just from their YT videos:
https://www.youtube.com/c/1Gunsite/videos