Figured I’d share what happened for anyone interested.
Previously, I tried to see if I could print a 40mm projectile for plinking with.
Mind you, this printed projectile is hollow, with only 15% infill. Excluding the perimeter, it is 85% air. The thickness of this shells is about .021ish of weak plastic.
I recorded video of someone else firing a shot.
The round is disintegrating in the bore.
The projectile is minie ball shaped. I think it is failing at the cup like bottom, splitting apart. I may try a flat base to see if that works better.
The infill pattern is rectilinear. Sort of like a honey comb, but triangles instead of hexagons. This leaves vertical open columns all the way from the bottom to the top of the printed projectile. I may switch to a different infill pattern. Perhaps something like gyroid.
In any event, I found some of the blue plastic caps (windshields) for reloading 40mm, so I will be able to make some proper chalk reloads with those.