A very good conical for that gun would be the Buffalo ball-et
in 270 grains. I shoot them out of my 1:48 barrel and get very
good groups. They are very cheap too. I would try about 70 gr.
of powder to start. If you get good groups you can increase the
charge some, to about 80 gr. I wouldn't go much more than that
as it is unnecessary IMO. I plink sometimes with 40 gr. or less and
the accuracy is astounding with these bullets. Good luck and keep that bore clean. With Goex you will be swabbing alot between shots. Scrub that bore good when you get home too as Goex contains alot of sulphur and will rust your gun's bore real bad if not taken care of properly. Use a
protectant such as Birchwood Casey Sheath (my favorite) inside the bore when storing it.
Good luck and ask us members lots of questions cuz we live for that.