making a HEAVY sandbag
 

I've become a real fan of sandbag lifting (especially shouldering, bearhug squatting and cleaning&pressing are great fun). Now the problem is I'm getting close to my bag's maximum capacity: I'm using an army duffle bag and it can only store about 75kg worth of pea gravel... Any ideas on how to make it heavier without going for a bigger bag? I've tried looking for lead shot, but here in Belgium they just don't seem to sell the stuff in smaller quantities (read: less than 1 ton's worth).
Any ideas would be greatly appreciated.

gravel plus sand to fill voids.

Like Dave said. Just fill in the empty space around your pea gravel with sand.

Why use pea gravel? I built mine using sand and I can get my bag up to #225 easy. I just use a contractor bag and fill it with 25lbs of sand and then tie it shut. Place that bag in another contractor bag and tie that one shut to keep it leek proof. I then just make multiple 25lbs bags and fill up my army bag. Works great an they easily fit. Here is a link showing how I did it if my explanation didn't make sense. http://www.goodyearbjj.com/fitnessblog/?p=21 (work safe)

My heavy bag is filled with sand + chain. Happened to find the chain for free, which was nice!

For some reason the contractor bags I have all leak easily (small holes at first, big rips later). And the heavy duty contractor bags I use now are the woven plastic type, so even when I fill them with pea gravel there is some dust loss.

@Craig: thx for the advice, I think I'll try pea gravel + chain and see how that plays out!