Re: Testing new loads.
I use a rest that appears to be an older version of the Sinclair Generation 2. Mine has bolts securing the sides and a slightly different front stop. That and a plain rabbit-ear rear bag. While I do agree with practicing the way you will shoot in the field, I think you're best served to test ammunition with as few variables as possible. That's where the most solid front rest you can get your hands on serves you better than using your bipod or backpack. For practice, absolutely. For load testing, remove as much "human" error as possible. It's a test of the ammo, not a test of you.