welcome zeener ! this isnt rocket surgery . but you have to be carefull and ALWAYS respect this black powder as it can burn very bad ...ask me how i know .....
just start small . noone ever sets a lap record on the first lap .
start with small charges like 20 grs ffg . and just get used to the routine of loading it / cleaning it .
honestly after seeing what i've seen in this sport , you could be wanting to see that 1/4 mile with a cap full , and carried away ...two times
you are not likly to get a 1/2 mile anyhow probably not even a 1/4 mile ..... the fun of a mortar is watching the ball in the air , and you cannt do that with much powder .
start small you'll be fine . IMHO small mortars are the way to begin to learn this stuff .
welcome
gary