Just get some Zircon sand, dry it out and fill the bag tight. You can try other sand, but ultimately this is where you will end up. After a while you may need to top it up if the bag sags or the sand settles.
You are going to probably or possibly see a change in POI or grouping from rifles tested in the original bag. The Caldwell bags stick to fore-ends causing them to jump or release inconsistently. They're OK for a quick sight in, but beyond that need junking. Same same for the rear bags.
Deer hide bags slicked up with talc or bags made from Cordura are about as good as it gets to get the best rifle potential.
Depending on who you talk to there is a case for bounce affecting groups if the bag is too hard. Some will try multiple bags packed with more foregiving material, whatever that is. The reason i say this is that bounce is a function of poor stock design or poor material. A good stock will work if the front rest was a house brick. Some bags i have seen over the years are about as hard as a house brick, which actually contravenes BR rules. It was said to me that in past years that a little cement was added to the sand where over time the bag would set like concrete. In BR terms that was and still is illegal, but it seems that there is a train of thought a bag can never be too hard. I don't know as i never did it.
While this is really more about rear bags, it is still worth a read and the sand used is applicable to front bags as well.
http://www.6mmbr.com/sandcomparison.html
What I really want to know is how hard I should pack it with sand? Rock hard? Still pliable, or is this another BR secret that only comes with years of intricate experiments?
