.40 Smith & Wesson / .40 S&W
Date: Mar 04 2015
Notes from the Lab: .40 Smith & Wesson / .40 S&W
The .40 S&W was formally announced in 1990 as a joint development between Smith & Wesson and Winchester Ammunition. It can be housed in most 9mm size pistols but is of a larger caliber and greater power and offers increased magazine capacity and less recoil than the .45 ACP. Its appeal has been widespread with law enforcement and competitive shooters and it serves for personal protection and field use. Loaded properly, it can be accurate.
With many auto-loading pistols being manufactured all over the world, along with domestic and foreign ammunition manufacturers, problems have surfaced that handloaders should be aware of. For instance, cases with very thin walls have been discovered. When these are sized and neck expanded, they are too thin to achieve proper bullet-to-case fit; bullets drop into the case with little or no resistance and can rest on top of the powder charge. This makes it difficult to maintain correct overall cartridge length, and applying a taper crimp still results in insufficient bullet "pull." A firm case-to-bullet fit and taper crimp are both required to produce reliable ammunition that will not allow bullets to "deep seat" when cycled in an auto-loading pistol and also aids with accuracy. Excessively thin cases should be discarded. All data herein was developed using Starline cases, which were uniform and gave proper bullet-to-case fit.
Various Glock pistols chambered for the .40 S&W have what are generally known as an unsupported chamber (which is not technically correct, but is how it is usually described). Fired cases often have a large bulge on one side just forward of the head. This is commonly referred to as the "Glock Bulge". This cannot be removed by full-length sizing cases and often causes difficulties when chambering reloaded cartridges. A great solution is to use the Redding GR-X Push Through die with E-Z Feed push rod. Cases can be pushed through this die to completely remove the bulge. Next they are full-length sized to be brought back to industry specifications for reliable chambering.
Maximum average pressure is currently established at 35,000 psi. In such a short case, small changes can substantially change pressures. For example, changing primers or bullet seating depth can change pressures by up to 10,000 psi. The use of small pistol primers only is suggested (with Winchester small pistol used herein). Special care should be taken to seat bullets to their listed overall length.
Always taper crimp bullets, preferably as a separate step after bullets are seated. The accompanying data was developed with a taper crimp that measured .423 inch at the case mouth (measurable using blade calipers).