Dense, easy-to-access material? I'm not sure if this is the right forum to ask this on, so please tell me where to put this if not!

I'm trying to make weights to lift at home, and I found online that using gallon milk jugs and filling them with sand or something similar is a good way to do it. However, I'm trying to make about 25 pound weights, which I'm not sure the sand would be heavy enough for. Am I wrong in this? What would be a good, easy-to-access (and not too expensive!) material that would reach at least 25 pounds or so in a milk jug sized container? What other way could I reach a weight of that size with easy to access materials, other than milk jugs?
Steel weighs 8000&nbsp;kg per cubic metre, or 8&nbsp;kg per litre.  A US gallon* is 3.79&amp;nbspl, so a gallon of steel weighs 30&nbsp;kg or 66&nbsp;lbs.  Unless you buy it in one piece you won't get perfect packing but you'd only need a 37% packing fraction to fill that gallon.  Identical ball bearings should get more like 60%, but ball bearings aren't cheap.  Old nuts and bolts would work if you can get them cheap.

At this point though, your milk bottle wouldn't survive long - it isn't designed to take the weight - so you need a stronger container, or to fill it first with steel then with epoxy (including the handle) effectively using the bottle as a mould.  That much epoxy would add  another couple of kg (~4&nbsp;lbs) and could get expensive (though there are cheap types ).

Wet sand would actually only need 1.5 gallons to reach 25&nbsp;lbs. Sand-filled epoxy would be similar to wet sand - you'd need to mix it well in another container, using just enough epoxy to fill the gaps in the sand.  This is strong.



* Apparently a common size for plastic milk bottles in the US