What is your favorite caliber to handload in custom chamberings

[loadnplenty]

Mine is my 257 Roberts Ackley Improved. It's favorite recipe is 115 Berger bullet pushed by 50 grains of Hybrid 100V for a velocity of 3180 FPS out of a 21 inch Douglas barrell. Group size, 4 shots covered by a dime at 100 yards from a sandbag rest.

 

[Gun Guru]

Mine is a .30 Hammond. That's a 378 Weatherby necked down to 30 caliber with the shoulder blown out and the belt turned off. A pound of powder don't last very long.

 

[loadnplenty]

I can imagine the powder doesn't!!!

 

[BHJ]

I've been working on an obsolete cartridge lately. It's an old black powder cartridge the .32 rimfire shot. I located some brass thats supposed to be used with a .310 round ball at Dixie gun works with an offset primer pocket but it's kinda pricy. It is turned from bar stock and uses a .22 starter pistol crimp. I'm using egg crate for a wad and loading 70gr of #9 shot over 10gr of FFFG black powder. The shot is held in hand rolled tubes of typing paper glued along the seam.( drinking straws fly out as a single projectile) A precarious process for a mouse gun but not many people this century have fired one.
These shells fit my Stevens favorite smoothbore chambered in .32 shot.

Anybody with a better idea for a parent case please chime in.
Here's a pic
left to right .38 spcl .32 rimfire milled barstock, .32 rimfire experimental with a drinking straw, .32 rimfire paper, 410 2 1/2" handgun load, 410 3" high brass birdshot
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[loadnplenty]

That is a new one on me lol