The 130g weight spec'd is the the flashlight and head strap together, no battery. I don't know why they did this, but it's the only thing that makes sense.
The actual weight of the HD20 with no battery, no clip is 87g, not 130g.
Here's proof --
Calibrated base. Need to lift the lights off the scale surface because the tail magnets effect the scale:
HD20:
FireFlies PL47 (78 g spec'd):
Eagle Eye X1R:
Sofirn SP40 (63 g spec'd):
HD20 head strap:
So if you add the weight of the HD20 and it's head strap, my measurements result in 87.0 + 45.8 = 132.8 g, close to the spec'd 130 g weight. I don't know how else to explain it.
I wish Wurkkos would clarify their specifications - this causes great confusion. Yes - the HD20 is a heavyweight for a rt. angle light to be used as a headlamp. But it's only about 9 grams heavier than a PL47, 14 grams heavier than a X1R (18650).