So I stumbled upon this while dealing with clowns in a candy tube. My legendary archers kept firing at the clowns but none of the bolts ever got their way to them, but rather fell onto one floor in the middle. I searched the net but no one seems to have mentioned it so I decided to utilize it to make an infinite archery range which also can be used as an ammo splitter. Here's the setup, bottom-up
On the first level, in the right is the (hostile or wild) creature to
intimidate stimulate the archers.
On the second level, there's a well. That's to prevent the dwarfs from jumping down to brawl with the creature with their bare hands, which often results in their own oblivion. Why it would work, however, is beyond me. Maybe the well just reminds them of Urist McMelancholy, who plunged into a well and never came back?
On the third level is the floor to catch all the bolts fired. You can put a stockpile here to give them to a smelter or another stockpile. You can also set 'claim fired bolts' order so you'll be freed of the hassle of manually unforbidding them. (But remember to cancel the order when facing real enemies!)
On the fifth level is another well, similar to the one on the third level, but to prevent the dwarfs from jumping down to get the bolts laying on the floor. Dwarfs are quite suicidal... 
No they won't. This well is unnecessary.
On the sixth floor is an up/down stairway to station the marksdwarfs. You may notice that the left side stairway is four tiles away from it. It's the minimum required distance, elsewise your dwarfs will simply stand on that stairway rather than going to the right stairway.
On the seventh floor is a floor hatch covering a downward stairway. It's to prevent the archers from firing when they've just moved onto that tile, so to prevent the ammo from hitting the stairway below, or getting their way to the creature. However, if more than two dwarfs move through the hatch in succession, the latter ones might fire through the open hatch.
I'll see if I can prevent it somehow. Edit: Yeah, Skullsploder mentioned you can use 'defend burrow' orders to station your soldiers on one tile. Based on this idea an improved version of the design came up.
The upper well has been removed. Make a burrow containing the right downstairs tile and the tile the creature occupies, set defend burrow order on it, and switch to the alert.
As to the creature selection, you may want to pit a creature that's non-flier, non-climber, and who can't breath or shoot or hurl fireballs at your marksdwarfs and bolt-collecting civilians. Clowns are the least recommended, despite their remarkable contribution to the discovery of the method. And for safety's sake, you may want to pit some creature that's tough enough so they won't die from a single bolt hit yet weak enough so they'll not beat your dwarfs to death. (I'm not 100% sure the two wells will at all prevent them from jumping down. They'll break one or two limbs but at least they'll live)
Test shows that, even with legendary crossbow and archery skills, a dwarf rarely send their ammo through the bend and all bolts just drop and sit on the floor for easy retrieval.
Tested in 0.40.24 with dfhack. Any thoughts?
Edit: fixed a typo
Edit 2: added a new design
Edit 3: by further research it is showing some weird behavior. If you station only one marksdwarf in one splitter he will not miss most of his bolts. But if you increase it to two dwarfs their bolts will miss virtually 100% of the time. And even weirder is that when you remove the newly added dwarf the first one will continue to miss all of his bolts. I guess more SCIENCE will be needed.
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Topic: New generation archery range & ammo splitter. >99% recycle rate! (Read 15907 times)