Mauser69
Member
Anybody here slug their barrel for a .40 S&W to check groove diameter for loading cast bullets? Are the majority of .40 S&W barrels larger than .400"? If so, why are all .40 bullets available in only .400" or .401"?
I have been developing range loads with Missouri Bullet Company 140g cast bullets with a BHN of 18 (hard cast), and I have significant leading in all of my guns. The MBC technical info says that the optimal pressures for a BHN of 18 should be between 20,000 and 25,000 PSI for proper obturation. The test loads I have used are estimated to generate between 20,000 and 30,000 PSI, and have a measured velocity between 875 fps and 1075 fps. These numbers all indicate that these loads should NOT be leading the barrels if they are the correct size.
I have four different .40 S&W pistols, and they ALL measure greater than .401" (measured with a micrometer, not calipers):
Star FireStar = .4015"
Dawoo DH40 = .402"
Ruger SR40c = .402"
Taurus 740 Slim = .4015"
Of these pistols, the Ruger has the worst leading problem, and the FireStar and Taurus have the least leading.
So that seems to be the problem - These bullets (and all other cast .40 I have found) are specified as .401", and the correct size cast bullet is normally .001" - .002" over the groove diameter, which means my guns would all need an unobtainable .403" bullet! What is wrong with this picture?
I have been developing range loads with Missouri Bullet Company 140g cast bullets with a BHN of 18 (hard cast), and I have significant leading in all of my guns. The MBC technical info says that the optimal pressures for a BHN of 18 should be between 20,000 and 25,000 PSI for proper obturation. The test loads I have used are estimated to generate between 20,000 and 30,000 PSI, and have a measured velocity between 875 fps and 1075 fps. These numbers all indicate that these loads should NOT be leading the barrels if they are the correct size.
I have four different .40 S&W pistols, and they ALL measure greater than .401" (measured with a micrometer, not calipers):
Star FireStar = .4015"
Dawoo DH40 = .402"
Ruger SR40c = .402"
Taurus 740 Slim = .4015"
Of these pistols, the Ruger has the worst leading problem, and the FireStar and Taurus have the least leading.
So that seems to be the problem - These bullets (and all other cast .40 I have found) are specified as .401", and the correct size cast bullet is normally .001" - .002" over the groove diameter, which means my guns would all need an unobtainable .403" bullet! What is wrong with this picture?