How do you go about bench testing a slug gun to find out its accuracy potential?

I have a Remington 870 pump and this is what I do:

I put the bottom of the receiver (near the bottom loading gate) on top of my Hart rifle rest and use a sand filled "bunny ear" bag at the back. When shooting, I hold firmly down on the forearm to control the "jump." I find that this works best for me.

I've seen many put the forearm right on the rest. Seems to me that there would be a lot of movement there.

How do you do it to get the best, most consistant results? Any suggestions?

because of the recoil, i dont fight the gun. I hold the forarm in my hand, place my hand on the bag/front rest. No bag in back. This lets me and the gun recoil together. I make sure i am sitting up straight so the shoulder fits flat on the recoil pad, another pad under my elbow,trigger finger arm. When watching other shooters, i have seen the rest rock under recoil causing the shots to string vertically when shooters try to force the gun to stay put.

I use to use my Dad's Model 37 Featherlite Ithaca in 12 gauge. I had a smooth bore slug barrel for it plus a scope. Testing it at the bench is a REAL PAIN!!! the recoil is so great the gun jumps off the rest. I could only fire it three time, before my shoulder got sore which lasted for days. I now use a Browning Gold Deer Hunter in 20 gauge which has FAR LESS recoil.

Hello,
I have found that I shoot better groups with my hand under the forearm and on top of the rest.
John