I only shoot springers off a bench. I tried a Caldwell Tac Driver bag way back. The "V" the forearm fits in seemed to me to hold the gun too tight or puts pressure on the gun to the side contrary to the artillery hold. So now I use a plain shot bag like a mini pillow shape on top of 4 bricks, two long way two on top crossway, sometimes 6. No bag in back under the butt stock. I don't place my non-firing hand between the bag and forearm. I place that hand on the table close to my chest with the butt stock resting in the fork of the thumb and four finger, finger tips resting on the bicep of the firing arm. It's not exactly true but I like to say I hold the gun so loose if I coughed I'd drop the gun.
I use a set of Allens, front and rear that I got from Walmart for darn near anything.