Because of the long chamber in my 45/410 single shot pistol, accuracy is very poor with regulat 45 colt loads. I have read about using 444 marlin cases to load brass 410 loads and was wondering about using them to load 45 lc, thinking that would start the bullet a lot closer to the rifling.
Since the case capacity is a lot more than the 45lc case how much more powder should I try to achive a near factory 45 lc load?

Uhhhhhh.......

Think you are on your own here. Possibly, a program like "Load from a Disk" or "QuickLoad" may be of utility.

There's load data for longer cases, such as the .454 Casull, and .460 S&W, BUT.... is it at the pressure levels your gun needs to stay below?

DannyAbear
You could get 454 cases and load 45LC loads in them, or use slugs in 410! But I don't think 444 cases are wide enough to seal in the chamber they may even burst when fire with anything but mild loads!

look up 450 Mongo. Yes it does work if your chamber works for it , you may need to ream the neck for about half an inch to get it to chamber. If you have never reamed or turned case necks, you are in for a treat. LOL. It depends on how much you like to tinker to get something to work as to whether or not it's worth it.
I did it in a handi 45/410 . The results were okay.