Plastic air rifle pellets

When I signed in to upload this project I searched "pellets" and came upon this one. http://www.thingiverse.com/thing:388339
There may be others.
I make no claim to be the first to do this. Since I have the project and photos all ready to go, I figure I'll post it anyway since my own experiences might add something to the idea.
..........

(Edit: I recently made some nice ones with a resin printer. Check it out. https://www.thingiverse.com/thing:4712637 )

I've been playing with this pellet rifle (Daisy 880, .177 caliber) and wondered about printing pellets.
There are a few plastic pellets on the market, presumably for indoor target practice with low-power pistols. Others have metal inserts to make them more effective for hunting and plinking.

I printed a few. One thing was immediately clear. Printed plastic pellets are very high speed. They weigh next to nothing so this is understandable.

I tried different configurations...Straight cylinders, balls at the end of hollow cylinders, rounded cones, etc. but the standard, waisted pellets with a hollow skirt is the best so far.

They aren't very accurate. I tested a few indoors and would be happy to keep them in a 2 inch circle at about 10 yards. They have a terribly rough surface and you can expect large groups and some flyers.

This same pellet design is also the fastest. Surprisingly it broke the sound barrier (see photo) but I wasn't prepared for a sonic boom (probably a crack) and didn't hear one over the other noises. [Edit: The crack is definitely there.] Speed was measured at point blank range with a rifle. A light pellet will slow down much sooner than a heavier one.

[Moved back 8 feet (~2.5m) from the chronometer, FPS dropped to about 980, so it lost 200 feet per second (~17%) in just 8 feet. That's a terrible hit on speed.... but what's worse is it lost ~1/3 of its impact energy.]

At 10 yards it still hits very hard. They flatten out somewhat if the target is paper, like cardboard, and sometimes ricocheted all the way back to me. For my rifle at near maximum power, penetration was about 6 or 8 corrugated cardboard sheets (from standard shipping boxes) at about 8 yards.

They are delicate at the thin waist. Be careful when removing them from their rafts. Best to cut them free with a razor blade. Tried no raft but they have a small footprint and don't stick well.

A set of nine pellets took 24 minutes and used just 1.5 grams ABS with a raft, 0.15mm Z, slowest speed. Also used fan cooling. These are really tiny prints and when it comes to pellets, accuracy is everything. Give them all the help you can.

Metric version included.