Ed Harris
posted this
12 November 2010
When I was at Ruger we did a great deal of testing with normal production DA revolvers trying to find the best configuration which worked well with either lead or jacketed ammo, and also when using .38 Special ammo in a .357 chamber vs. in a .38 Special chamber.
Most important of all is correct cylinder timing and alignment. After that comes bullet fit in the ball-seat of the cylinder.
Cylinder must “range” perfectly on all six charge holes with no “tickers” of the range rod.
Bullets must fit the ball seat to exact size. More than .0005 smaller or larger will enlarge groups due to bullet deformation.
Ball seat diameter should be no smaller than barrel groove diameter and should not be larger than .001 over SAAMI max. bullet diameter for lead bullets. When shooting jacketed bullets ONLY ball seat should be bullet size and not larger than max. bullet diameter. For jacketed it does not hurt if up the ball seat is as much as 0.0015 smaller than barrel groove diameter, tighter is better in calibers such as .30 M1 carbine and 9mm Luger when firedd in revolvers.
Diameter of forcing cone entrance should not exceed 1.05 times SAAMI max. bullet diameter, as larger forcing cone opening increases heat checking with jacketed magnum loads and leading with .38 Special loads.
For jacketed bullets forcing cone angle doesn't matter within reason if smooth and concentric and revolver is correctly timed.
For lead wadcutter bullets shallower forcing cone angle is better. 11 degrees was better than 18 degrees, but with perfect cylinder timing and bullet fit outstanding accuracy was obtained with 6 degrees included angle, also worked splendidly with all jacketed and magnum ammo.
Accuracy of .38 Special lead bullet ammo was improved in .357 chamber if shoulder angle at front end of chamber to ball seat transition was reduced from standard 15 degrees to 6 degrees included angle.
If standard SAAMI chambers are used .38 Special wadcutter ammo fired in .38 Special length chamber is about 15% tighter than firing same ammo in a .357 length chamber. With reduced transition angle at front of chamber difference was not significant.
Best guns in GP100 configuration would shoot sub-two inch 12-shot 50 yard groups with selected lots of magnum ammo from Ransom Rest and would also do so with good lots of target wadcutter. This equals experience with Colt Python and Officer's Model Match which was the standard of comparision. Design intent was to build a “poor Boy's Python."
73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia