Try this advice from ....
a Benchrest Hall-of-Fame inductee.
SAND BAGS & HOW TO FILL THEM By Speedy Gonzalez
Back in the old days, about the time Fred Flintstone was still alive, I worked for Pat McMillan for free, from time to time to learn all his secrets.
One day little Speedy was filling some new sand bags out behind Pat's shop, stuffing them with more sand than Taco Bell put beans in their Burritos. When Pat stepped out the back door and inquired as to what in the hell was I doing packing them there bags the way I was.
I looked up at him with eyes like a kid with his hands in a cookie jar. My reply must have sounded like Homer Simpson "Doooh". Finally I said "I don't know, Boss. I just thought you were supposed to fill these babies up and go shoot. I got that "You dumb bastard look" from Pat and I knew it was lecture time.
Speedy! Speedy! Speedy! (Now, I knew I had best go get a coke and a sandwich. We were gonna be here a while). This was what he told me.
You can not have two bags filled so hard that you gun bounces on them in the process of firing round at your target, especially if you have a rig with a very flexible stock. The bags must be set up in a manner for them to absorb the initial shock of the firing pin moving forward and igniting the primer. Then maintain their shape and absorb the second shock wave as well the rearward thrust and torque of the rifle.
What happens to the rifle when this is not done? Well let me tell you. The rifles have a very bad tendency to jump and roll in the bags. This causes many of those wild, lost shots that one can't explain. You know! The one that should have been in there and is now sitting all by itself like the red headed kid nobody likes. (I’m not talking about you Bill Dorsey, I still love ya man!)
Charles Huckaba, Ken Terrell, Larry Baggett and some of us Texas shooters talk about this phenomena quite often. We have all agreed that -
1: You can not have two hard bags in your set up.
2: Heavy sand magnifies these phenomena.
3: If you are a bag squeezer, pack ears hard and leave bag pliable enough to squeeze for the movement required. You may pack front bag as hard as rules permit.
4: Free recoil shooters pack both bags firm, but not so hard as to allow stock jump. Especially if you have a stock with a very flexible forearm.
***5: We use play ground sand also know as silica sand. I sift mine to get any large impurities out then mix it with 25% to 50% with Harts parakeet gravel to the desired hardness that I am looking for. The bird gravel keeps the sand from packing itself into that solid as a brick state.***
Speaking of bricks another thing that happens when shooters employ that heavy zircon sand is the ears form a low spot under them from recoil and then tend to rock back and forth with the rifle causing many low shots to crop up. Edgewood makes an Edgewood/Speedy rear bag specially reinforced under the ears to eliminate this scenario.
One last note if you use the new Cordura bags keep them sprayed with a good silicon spray or "Rain-Ex". This keeps them from getting sticky.
Well, Boss try that and see if it helps.
Speedy
P.S.: I do not like the double stitched leather bottoms. While this seems like a good idea, I see more shooters have problems because of them. They tend to slide around the bench and or slide with the rifle on recoil. The standard Protector with Cordura rabbit ears and an Otto ring bag with A Cordura front would be what I would suggest to the new shooter or one of the Edgewood / Speedy rear bags.
Source:
http://benchrest.netfirms.com/Benchrest Basics.htm Art
