I've been playing (yeah best description I guess) with my 3D printer and recently got some TPU material. A flexible plastic that works reasonably well in my stock machine.
Printed several items, different finish from the base PLA material. But it's way flexible. Holds shape well when several layers thick.
Tried a speed strip off Thingiverse, but it wouldn't print worth a darn, and I didn't like how it was designed. Loads would come out too easy.
So I reworked it and have printed some 5,6 and 7 round for my 38/357 revolvers.
Yeah, I could have bought a dozen for what the roll of material cost, but what is the fun in that?