According to QuickLoad, AA5744 is a tad slow for 250gr bullets. For the same 80% case fill, you are giving up 200fps as opposed to an 80% fill of Lil Gun and you'll be blowing 10% of the AA5744 out the muzzle unburned. The good news is an 85% fill will bring you up to the Lil Gun velocity and not be pushing the pressure limit unlike Lil Gun, which would be over pressure (SAAMI) at 85% case fill.
According to QuickLoad, start with 37gr of AA5744 with those 250 XTP's seated to yield a COL of 2.15 and work up, watching for an accuracy node.
Hoot