I posted the following on gunsmithing with no responses. Can anyone comment?

I have read/researched a lot of articles regarding the 45 Colt recently, and have learned that there is an incredible amount of variation in chamber, chamber throat, and barrel groove diameter size in the various 45 Colt sixguns available. I have learned this from first hand experience as well. My current experiences include a few stock Ruger Blackhawks and a United States Firearms single action put together and finished by Doug Turnbull restoration. Two of the Rugers (both made within the last six years) started out with undersized chamber throats of .449" to .450" and barrels with .451" groove diameters. They both grouped .454" lead factory loads from Black Hills, Winchester, and Remington, like a shotgun pattern at 35 yards. I then put together a similar load using commercial "Laser Cast" brand, 250grn .452†bullets over 6 grains of Red Dot. These rounds shot equally bad in the Rugers. It was at this point that I decided to slug the chamber throats and barrels of the Blackhawks and found the tightness. I had the chamber throats on one of these revolvers opened up to .452". This improved accuracy with the handloads immensely. However, the .454" bullet factory loads still shot as poorly as before. The third Blackhawk in this story (I’m not sure when it was made, but it seems very old. It was bought at a gun show.) has the same barrel groove diameter as the other two previously mentioned Blackhawks, but the chamber throats measure .458†to .459†in diameter. This pistol doesn’t group any load worth a hoot. I have read that the base of the bullets in the soft-alloy .454†factory loads should obturate and slug up to the chamber throats, but I am not sure if this is happening. Leading and accuracy are terrible with all loads. The last gun I have experience with is the USFA/Doug Turnbull Single Action Army clone. It has .452†throats and a .450 groove diameter. It shoots .451†to .452†cast bullets pretty well, but larger diameter bullets are worthless. The most recent load that I have tried, which was taken from an article by Brian Pearce in “Handloader†magazine, consists of the RCBS 45-270SAA cast bullet (mine end up weighing 285 grains cast out of wheel weights and lubed with LBT blue soft) over 11.5 grains of HS-6 for about 1,000fps in 4¾†barrels (pressure is listed at under 19,000psi and OK for use in post-war Colt SAA’s.) This bullet measures right at .454†after it has cured for 24 hours. I reduce these down to .452†for use in the modified Ruger and the USFA single action. This load shoots well in these two revolvers, and there is virtually no leading. At this point you’re probably wondering where I’m going with this rant. Well, sometime when I can afford it, I would like to have a very high quality Single Action Army clone made up in 45 Colt that shoots factory loads containing .454†cast bullets and the above mentioned heavier load both very accurately and very cleanly. Based on what I have read, I think I need the following for utmost accuracy and cleanliness:

1) Minimum SAAMI chamber size of .480â€, with chamber throats measuring .4545â€.
2) A barrel with .452†to .453†groove diameter, and .444†to .445†land diameter.

Can a well informed and experienced person comment on whether or not I am on the right track given my criteria? Should I go with a .453†to .454†groove diameter barrel instead of .452†to .453†groove diameter? I’m thinking that it really won’t matter much between the two diameters, but I am looking for the very best accuracy possible from a best grade arm made by someone like Hamilton Bowen. If I’m going to spend $2,500 or more on a high quality custom revolver, I want it to shoot as good as it possibly can, and this gun will be shot regularly. Does anyone know who makes cut-rifled 45 caliber barrels with these specifications? Any helpful comments would be greatly appreciated. (By the way, I know that the pistol has to be built right, with good barrel to chamber alignment, proper barrel-cylinder gap, etc., etc., so pleased don’t comment on that.)

The original groove diameter of the 45 Colt was .454" but was then [afterWWII ?] changed to .451. In general jacketed bullets should be groove dia and lead bullets .001 larger. The revolver complicates things by having a cylinder throat .In the case of a .458 throat the bullet expands to fill the .458 then in the barrel is squeezed down to .451 !! This is not good for accuracy. I would use the .454 bullets only in a .454 barrel and use an appropriate throat.