Dsm:
I'm sure everyone has their preference. However, here is a summarized version of what Speedy had to say on the subject when I researched the topic for myself a few months ago:
SAND BAGS .... By Speedy Gonzales
2 hard bags cause guns to bounce when firing a round. Bags must absorb the shock of the firing pin moving forward and rearward rifle thrust and torque. When this isn’t done rifles jump and roll in the bags. This causes wild shots. Some Texas shooters agree that:
1. You can't have 2 hard bags.
2. Heavy sand magnifies the problem.
3. If you squeeze bags, pack ears hard and leave bag base pliable for required movement. Pack front bag as hard as rules permit.
4. Free recoil shooters should pack both bags firm, but not hard.
5. Use play ground/silica sand. Sift, then mix with 25 to 50% of Harts parakeet gravel.
Heavy zircon sand causes ears to rock back and forth and low shots. Edgewood/Speedy rear bags eliminate this. If you use Cordura bags spray with pure silicon or Rain-Ex.
Double stitched leather bottom bags slide with recoil. Use standard Protector with Cordura rabbit ears, an Otto ring bag, and a Cordura front bag, or an Edgewood/Speedy rear bag.
Hope this helps.