[mlangsdorf]

For rifle caliber bullets, 3G3 suggests roughly a 3:1:3 ratio of bullet mass to propellant mass to casing mass. A caseless round should weigh about 4/7ths an equivalent cased round - and when you consider that you're really evaluating TL6 cased rounds with moderate REF propellants versus TL8+ caseless rounds with higher REF propellants, you can get half the weight.

I can recreate the UT 10mm CLP pistol - one solution is a 10mm bullet, aspect 2, density 4.5 (which is fairly low - real bullets are usually around 7-10) for a bullet mass of 5.3 grams. Using ~14 grams of propellant at 43 kPSI and 5.5mm of burn distance, you end up with a velocity of 530 m/s and 3d pi+ damage, 1/2 ~150 yds, max ~1800. More reasonably you can use a density 7 bullets with the same propellant for a velocity of 425 m/s, same damage, and 1/2d 200 yds and max ~2200 yds, but then weight per shot jumps to 0.021. .40 S&W weighs 0.035 per shot, so you're in the ballpark of "half the weight of conventional cartridges."