Hope that helps.Actual bbs made of steel or copper are worthless except for the lesser pistols or automatic guns. 3 of them is still significantly lighter than a single 1/4" steel shot and the ghetto construction will result in less accurate flight.
Size bb lead split shot is good for most pistols and mid-range guns but is somewhat lacking in high-powered rifles.
1/4" steel slingshot ammo is good for the best variety of guns in my opinion. They're only slightly too heavy for my SSII and only slightly too light for my Max Shot. In addition, they're completely spherical and slightly cheaper than fishing weights.
3/0 split shot is slightly heavier and will work better than the 1/4" steel shot in high power rifles, but at the cost of reduced performance in lower powered guns.
Size 7 lead split shot will get the most out of your homemade or sm5k, but is rediculously heavy for most guns.
After trying all of the above, I've ended up just using 1/4" steel shot for all my darts. I don't use uber long range rifles because I don't like the ROF and my SSII is pretty high powered for a pistol so this is a good weight for all the guns I actually use.
From my experience with micros, I'd recommend one bb size fishing weight per dart. With a substantial amount of hot glue, it won't lag too much in high power guns. It works way better in weaker powered guns than darts weighed with 1/4 steel shot or 3/0 lead split shot.
I have a few questions on this myself:
Do the lead split shot sizes vary from brand to brand, or are they universal sizes?
My last trip to Walmart yielded no 1/4 steel shots. Where exactly in walmart do you find these?