The last Dog Gone Good Darrell Holland rear bag was heavier fill. I called. The guy rattled off alternate fill material and how to get it in there.
http://www.dog-gone-good.com/

Here he is talking his really big bench shooting bags
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Bag Filler

Bags can be shipped empty, or filled at the factory for a small fee. Filled bags also require an extra $5 packaging fee. The bags can be filled with polypropylene regrind which can be found where plastic is recycled (check yellow pages under lastic). Large bags will weigh about 22 lbs., medium bags about 13 lbs, small bags will weigh about 10 lbs. Ground walnut tumbling media will weigh about the same as polypropylene. Sand will weigh 60 lbs. in the large bag and about 45 lbs. in the medium, and the small bag will weigh about 30 lbs. For a light weight filling Buckwheat hulls can be obtained at a feed store and the large bag will weigh 6 lbs., and the small bag will weigh less than 3 lbs.

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