I have a reloading request from a customer
make some 38 spl shotshells. for a deringer pocket gun.

Using say Bullseye powder and #9 shot,
what powder charge should I load it with?

Speer #11 shows 4.5 grs of Bullseye using their 38/357 shot capsules with #9 shot.

2.8 -3.2 grains of Bullseye will work depending on the weight of the capsule and shot. This load is for a MODERN .38 Special revolver.

Speer shot capsules for 38 special have load data with them. I uses 5.5gr unique. Works good.