The starter pistol loads I have seen have been blackpowder. You'll likely do better with a FFFG or FFFg than a coarser "slower" FFG....
If you are reloading these, I'd be careful of a few things... I'd be strongly tempted to try to clean the fired cases some time soon after firing. Deprime FIRST, and wash in mild soapy water. Rinse and dry (NO heat, just dry). Seat your regular small pistol primers.....
I would NOT repeat NOT use a normal powder dispenser for Black powder. Its entire possible I'm completely full of bovine excrement, but I "think" regular smokeless powder measures dont play well with BP (?).
Most starter blanks have a really heavy roll crimp. Lacking a bullet, I'm not sure how well the crimp is straightened out on firing. And regular pistol dies wont 'iron' out a heavy crimp. You might need to fabricate some form of tapered expander to iron the crimp out. I've got a set of cheap taper pin punches. They are round, and the specific diameter working end then flares to an octagon bar stock handle end. Find the right punch, saw off most of the working end, leaving a bit of the round stock and taper. Lube it generously. This might be your new crimp removal tool, or at least enough to open it up sufficently for the case mouth belling die to work without crushing the case wall.... Its going to take some experimentation. Youre not loading bullets, but youre going to need case walls sort of straight for wad seating and retention.
I used to make wads for snake shot reloads in .38 and .44. I'd take one fired case, drill the primer pocket out to about 1/8, or 3/6", and use my case mouth chamfer tool to sharpen the case mouth to a knife edge. Do the inside only. Place thin cardboard (cereal box material, etc) on a soft sacrificial surface (corrugated cardboard, soft pine, etc). Place case mouth down on cardboard. Give it a smart rap with a small mallet or hammer, use small nail to press out the newly formed cardboard wad by pressing the nail thru the drilled out primer pocket. You have a ever so slightly oversized wad that should snug fit inside a resized, primed, and charged case.
BP likes to be compressed, and air spaces over the powder are often regarded as "not good". I'd scoop powder, pour the charge into the case, and press a small dowel into the case to compress the powder. I'd seat a cardboard wad firmly down on top of the powder, and roll crimp over.
If you are careful, these should stand up to normal handling like loading. If you are concerned with cardboard over wad "loss" with handling, something like a swipe with clear nail polish on inside of case wall where it meets the wad should keep everything in place nicely...
You're playing a little "off the reservation loading these, but realistically there's no bullet, and there should be extremely limited pressures. its all noise and smoke, which is the idea.