what about using lead bird shot? we've got a bunch of bags of it for reloading shotgun shells. lead wont rust, and they are heavier than bb's so it would take less individual shot and i think they will fit through the valve stem with the core out. so what do ya'll think?
This is just a theory, but here goes. I wouldn't do lead. Reason being, the lead shot will encounter millions of collisions with the other shot. Lead being soft will deform and start to break apart, leaving lead "shreads". Doesn't sound like it would last.
I have 38.5/15/15 boggers i run 10oz iirc. of airsoft beads. they work great. after the tires are warm. i driven from wv to md and they work. I got them at walmart 10.00
i vote bb's
put some unbalanced tires on my bronco couldn't go over 30. then i put the BB's just in the front and could go as fast as i wanted.
42's would be like 12oz per tire. sounds like alot but worth it.
(even better to get air soft BB's, they won't react with water vapor)
Might not be enough. I had some 35 inch SSRs pad balanced at Galloway's. They spun balanced them first. (rotated the tire on the wheel to get the best tire/wheel cancel possible.) Then pad balanced them. Then fine tuned them with a few inner rim stickies. One tire took a 17.5 oz pad.
The whole thing was a waste of time and money. They stayed balanced less than a year and this is on a play truck not a DD. They actually wore out of balance.
Next time....golf balls. At roughly 1.5 oz each, I figure 15 in each wheel will do the job. I already got them free from friends that play....."You guys got any old golf balls I can have for free. Yeah I need 60 of them."
For 42 TSLs I might use 20 each.
FWIW, the equal isnt a powder anymore. They went to a small plastic bead (much smaller than a bb), because of the tire pressure monitoring sensors on new vehicles. I have the old powder style in the 35s on my towrig/dd F250, and the new bead style in the 38 tsl's on my 78 f150 trail rig. The 250 will run up to 90 with no shakes (thats as fast as ive gone), the 150 will run up to 65-70 before the tired 351m/4speed quits pulling
They stayed balanced less than a year and this is on a play truck not a DD. They actually wore out of balance. 
what mix % do you use and how much liqid do you think for a 37x13.5 tire?