This is a ridiculously niche item; a pocket ammo case/dispenser designed specifically for the infamous Lyman collar button 45-70 round. The design allows the slugs to rest safely on rails, keeping unwanted pressure spread out across the stronger radius' of the bullet. The bullets wont slide around, they'll roll like little lead train cars, which pretty much eliminates any chance of deformation.
The cap fits very snug, so you don't need to worry about spilling all your ammo into your pockets- leaving you with shiny lint balls instead of ammunition. There are a few variations included, but the one printed in the photo seems to be the sturdiest. I've yet to print or test the picatinny rail variation so I expect it to have a few flaws.
I use these exclusively with my Airforce Texan 45 cal air rifle, and find that a convenient portable ammo storage solution is a must. Though my ammo is sized to .456 I believe I've left the gap wide enough to accommodate up to .459.
At the moment the case holds 8-9 shots, which is the precise amount of shots I get before needing to recharge the rifle. You could easily scale it or mesh mix it to hold far more. The rail guides that the slugs ride on would also allow for a pretty easy looped design if you are so inclined... I'm not.
If I ever manage to get my Texan back to shooting larger 400gn shots I will likely design more cases to fit, but for now this is what I'm using.
I hope this comes in handy for the other three people on the planet that shoot Lyman collar buttons with a 45 cal air rifle and also happen have a 3d printer. I suppose muzzle loaders may find this useful as well, but who knows.
I also recommend a few drops of lube into the case itself to keep everything shiny and slippery.
printed the main body with the hole pointing to the sky, the cap with the flat back to the build surface. Since i hunt primarily in the black of night and tend to drop things frequently, I printed in glow in the dark.