My 45 seems to be very forgiving pellet wise.
While my range is fairly short, Benjamin Discovery in 14.3gr, FX 18.1gr., and JSB Exact Jumbo 18.1gr., JSB Exact Jumbo 25.4gr., are all about as accurate in my gun. I tried the 25gr. pellets this morning. Pretty much the same one hole per magazine count as the other pellets.
Don't know the pressure, but the speed was set by Charlie at Georgia Airguns at about 865ft./sec. (18gr) as I recall. He also set the trigger to be a two stage from a single stage as originally sold.
Like most guns, every gun / barrel is a little different. Even though two barrels may have been manufactured by using the same tooling and machining equipment, they "might" like two different setups. It's up to the owner to find what "he" and "his/her" gun likes best. Most all guns seem to like the JSB line of pellets.
I did a little work to my shortie -
Have fun with it.
Mike