shotgunning doesn't accelerate the cargo, it only separates it from the container
Why does my cargo fly 3x further then when I use max speed versus only a few ramps, and reach several z levels higher? It's definitely affected by cart speed. I don't know how to turn them into reliable frontal collisions, but surely it's worth trying a nested minecart frontal with another nested minecart, etc? It sounds tricky, but if it works, the whole thing fits in 1/10th the space and becomes vastly easier to build.
Edit: More information:
I thought this was too well known to bother writing a thread about my low grade !!science!! on shotguns and minecarts and whatnot, but maybe it isn't? I built a firing range fortress, loaded a minecart, and save-scummed for maximum comparability between tests, only taking the extra small bit of time to build walls or bridges as necessary, etc. to test different things. But in every case, the cart was loaded with a full load (86 or something?) of lead bars:
Test 1) 10 impulse ramps. Range = 28 tiles (middle of the bar spread on the ground)
Test 2) 50 impulse ramps, which should be max normal speed. Range = 76 tiles
Test 3) 30 impulse ramps. Range = 43 tiles
Test 4) Build walls to "choke" the shot for the first 3-4 tiles, simulating a narrow hallway. In real life, this would not affect absolute range but it would increase effective range by putting a larger number of low velocity pellets into the target in the central area (through ricocheting into a shallower angle), thus causing sufficient damage further out. In dwarf fortress, the range was unaffected in EITHER sense. The furthest bars were just as far, and density in the middle did not increase. Thus, it appeared that no ricocheting occurred, and seemingly not even very much or any "sliding" along walls after impact. Things DO definitely slide along the ground, but maybe this doesn't apply to walls? It seems almost like anything that hits a wall just stops dead and falls straight down.
Test 5) I tried building floors above the muzzle, same concept but vertically. Range was reduced notably. It was reduced more at higher powers. I suspect that what's going on is the bars that would have flown furthest were the ones that were randomly chosen to be at higher angles (parabolic trajectories, duh). Thus, when you block those from going as high as they need to, they fall short, and only the flatter trajectory bars make it out, which don't go as far. It's possible that like walls, they sort of stop dead on a ceiling too, but it was too hard to tell for sure. I could retest it and count the density of bars right at the muzzle afterward to find out if anybody cares. That said, I never saw any bars even at max power go more than 1 z level up from the launch point, so you don't need huge amounts of headroom.
Bottom line for this thread, though: ABSOLUTELY the cart going faster = faster projectiles that fly out of it. In fact it seems like it is probably a straightforward linear relationship, as you would expect in real life (the slightly nonlinear final range distance you have to realize takes into account parabolic math and thus would not be expected to be perfectly linear even if muzzle velocity were linear)