Muzzlenut.
I use leather sand bags on a portable shooting bench.
My shooting bench is a combination of 2 designs. The two sites are:
http://www.aeroaces.com/bench1.htm
http://www.larrywillis.com/shootingbench.html

I used the leg mounting idea of the 1st site, but used a 2x6 and cut the diagonal between 6" markings instead of 4 1/2" to make the wedges to angle the legs out. I also cut the 1 1/4" pipe to 29" to put the finished top very close to 30 - 31" high. that height allows me to use a 5 gal bucket for a seat, which doubles for carrying supplies to my range site.

I used the general shape of the 2nd site but modified the dementions to be 30" wide at the front and 14" wide at the back. Front to back remains 36". Used 2 layers of 3/4" plywood Which makes for a very sturdy top and is necessary for thickness to screw the leg flanges and wedges to underside of the table. I also like the stability of 3 legs for uneven ground.

I have 5 pics that show detail & finished bench. Check the link.

http://my1.photozig.net/jascoesens/Album1/photopage.html

Now after using this bench for 18 months, There are some changes I would make to reduce the weight. The bench as pictured weighs ~ 48 pounds w/ legs attached.
1) I would only double the plywood for 9-10" at the front and back for the leg mountings.
2) I would step down to 1 " pipe, which IMO would be plenty sturdy.