I have a friend who has a Hi Wall with a Badger 45 cal tapered round barrel and he ask me what would be the best bullet weight to try. We checked it and it has a 1 in 22 twist. Think he is shooting a RCBS 405 gr now.



JMH

Caliber      0.459      Inches            
Bullet Weight      405      Grains            
Bullet Length      1.02      Inches            
Barrel Twist      22      Inches/turn            
muzzle velocity      1200      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      3.07            

Caliber      0.459      Inches            
Bullet Weight      535      Grains            
Bullet Length      1.455      Inches            
Barrel Twist      22      Inches/turn            
muzzle velocity      1200      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      1.53                  
                       
Sg (gyroscopic stability factor) shouldn't be less than 1.4 (not enough spin - bullet will tumble).  If Sg is greater than about 2.0 (excess spin), you may gain some accuracy by going to a slower twist barrel or using a longer bullet. Also a heavier bullet (has greater kinetic energy) is less prone to wind drift and is capable of shooting longer distances. I would suggest going to a 500 to 535 grain bullet.                        
     

I used the more advanced Don Miller gyroscopic stability factor formula in my calculation above.
His more precise calculation expands the Greenhill prediction by including the environmental factors into the calculation.
Miller twist rule is a mathematical formula derived by Don Miller to determine the rate of twist to apply to a given bullet to provide optimum stability using a rifled barrel. 
Miller suggests that, while Greenhill's formula works well, there are better and more precise methods for determining the proper twist rate that are no more difficult to compute.

With the minimum bullet length you recommend and increasing velocity:

Caliber      0.459      Inches            
Bullet Weight      450      Grains            
Bullet Length      1.265      Inches            
Barrel Twist      22      Inches/turn            
muzzle velocity      1300      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      1.95                  

Twist is 22. We checked it three times with a tight fitting patch. I have a RCBS
500 gr round nose we are going to try. Think it is 457125? I would have to go look. Thanks guys...



JMH

In a conversation I once had with Ernie, I'd inquired about a different twist on a barrel blank.  If I remember things correctly, he told me I could have any twist rate I wanted in his 45 cal barrels, as long as it was a 1:18.    I think I purchased a half dozen of them with various twist requests and they all are 1:18.
So I'm inclined to agree with JKR's comment, yours is news to me.
JMH,
I do have a few others on rifles with a 1:20 and slightly less that shoot a 500g pill very well.  A Lott caliber comes to mind, in a big boomer, very accurate in cast, jacketed and monolithics.  Used in very hot and very cold extremes.   
I'd start with the 405g but I tend to lean towards slightly heavier as the distance grows.
GT

If I remember correctly the barrel on his gun was one of an order the now defunct Shawnee Rifle Co. of Warner Robins Ga made in the early nineties. They were to be used on 1877 Sharps rifles these guys were going to build. I just checked it again and it is indeed 1 in 22 twist. Don't know what else to say. Going to try a 500 grain and see if it improves.



JMH

Caliber      0.459      Inches            
Bullet Weight      405      Grains            
Bullet Length      1.02      Inches            
Barrel Twist      18      Inches/turn            
muzzle velocity      1200      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      4.59                  

Caliber      0.459      Inches            
Bullet Weight      450      Grains            
Bullet Length      1.265      Inches            
Barrel Twist      18      Inches/turn            
muzzle velocity      1300      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.92      

Caliber      0.459      Inches            
Bullet Weight      535      Grains            
Bullet Length      1.455      Inches            
Barrel Twist      18      Inches/turn            
muzzle velocity      1200      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.28                  
     
Caliber      0.459      Inches            
Bullet Weight      560      Grains            
Bullet Length      1.52      Inches            
Barrel Twist      18      Inches/turn            
muzzle velocity      1200      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.11                  
                       
Sg shouldn't be less than 1.4 (not enough spin).  If Sg is greater than about 2.0 (overspinning), you may gain some accuracy by going to a slower twist barrel or using a longer bullet