I use Power Pistol for my 9mm and a double charge comes to just below the mouth and is easy to see. That's with 4.0 gr and a 147 gr bullet, so that is likely to be the lowest weight you'd use. OTOH, with TiteGroup it's possible to
triple charge.
Somewhere there is a powder burn rate chart that also lists powder density; both cc/gr and gr/cc. You can use this to calculate how much of the case it will fill. To find the case volume weigh how much water the case will hold. 15.4 gr of water equals one cc.
The "somewhere" is
www.tacticoolproducts.com/powder.pdf