Proper sandbagging

In my quest to prove its me and not the equipment, answer its probably always me, I am wondering what is the proper or most consistent way to use a sandbag for bench testing. I am using my inexpensive rear bag designed for a rifle but would think a larger flat bag would be a little steadier. Are there bags I could look for better suited to the task? I try to at least get my elbows down but the set up doesn't allow me to get my forearms down. I don't think anyone near me has a ransom rest and if they do they probably do not have Buckmark inserts. I continue to plod along on my journey to becoming a bullseye shooter.

1 or 2 layers of plastic bag filled just short of absolutely rigid - need some "give" to get forearms/wrists nestled in - slide that into the cutoff leg of an old pair of denims - I had one end sewed shut and put Velcro on the other.
/B

I've had the best luck using a ridgid rest with dense foam on top. Doing the same for the butt. Building up under the butt until I can hold center on target with FIRM and EQUAL down pressure on both the butt and dust cover (or bottom of revolver barrel).  2¢ -YMMV                Good luck, Russ