I have seen CAP N BALL use the powder drop tube when doing a new gun test.
Drop tubes require careful management as powder can become trapped in the tube.
By way of example; a competitor in the Long Range World Champinships in the US a few years back loaded with a long drop tube, but the rifle wouldn’t fire. He used a gas blower to clear nipple and what he thought was powder, wad and bullet. Next shot fired went off with excessive recoil; he thinks the charge was stuck in the tube first time, hence no ignition. Second time, it’s probable that when loading, both the charge trapped in the tube and the new load dropped through - he launched his 550 grain bullet with around 180 grains of FFg.
So check tubes are clear and have your range rods marked so you can check if the rifle is unloaded, just has powder in, or has powder and bullet.
David