Some Safety Concerns About the .40 S&W

Some Safety Concerns About the .40 S&W

The .40 Smith and Wesson is an excellent defensive pistol round offering improved performance over the 9X19 mm in a similar sized package. Being a fairly short cartridge, the price of this performance is relatively high operating pressures. These high pressures are not a safety concern in themselves but they do present some potential problems that must be considered. Here are some SAAMI pressure standards for common rounds to give you an idea where the .40 stands in the scheme of things. The pressures are given in PSI.

.45 ACP 21,000
.45 ACP +P 23,000
9X19 mm 33,000
.357 Smith and Wesson Magnum 35,000
.40 Smith and Wesson 35,000
10 mm 37,500
.44 Remington Magnum 40,000
.30-30 42,000
.308 Winchester 52,000

The high operating pressure of the .40 combined with the short cartridge case means there is very little room for error when dealing with this round. The .40 is a true magnum round and is actually rubbing shoulders with some rifle rounds in the pressure department.

Gun powder develops a given pressure for a given amount of powder in a given volume. If you change the case volume without changing the amount of powder, the pressure will change. Increase the volume and the pressure decreases. Decrease the volume and the pressure will increase. The relationship between case volume and pressure is not a linear one; that is to say cutting the volume in half does not double the pressure. A very small decrease in the volume can cause a massive increase in pressure and not always a predictable one.

One variable that determines your working case volume is the depth to which the bullet is seated. Seating a bullet deeper in the case will cause pressures to go up. The .40 has such a small case volume in relation to its caliber that a very small change in bullet seating depth represents a significant percentage change in the volume available to the powder. Because the .40 has such a high operating pressure it doesn’t take much of a pressure increase to exceed the ability of the case to contain the burning propellant. A ruptured case can create all sorts of havoc and can be dangerous. A bit more pressure can cause structural failure in the firearm which is very likely to cause injury.

One action that may cause the bullet to be seated more deeply is the simple act of cycling the cartridge from the magazine into the chamber. Ideally the round will only make that trip once, however administrative loading and unloading may cause you to chamber the same round several times. Initially the setback may be insignificant but as the cartridge shortens the feed geometry will change and each feeding will shorten the cartridge by a greater amount.

As an example of what can happen, I was shooting a handload in my .45 ACP that chronographed right at 870 fps with Hornady 230 grain truncated cone FMJ bullets. With an 18 pound recoil spring the cases were ejecting six or eight feet. I had chambered one of the cartridges several times in a pistol that was giving me some feeding problems with that bullet profile. The bullet had set back visibly in the case. When I fired the compressed round over the chronograph I got a reading of 925 fps. The empty casing ejected over 20 feet. Examination of the case showed drag marks on the primer although the unsupported portion of the case had not bulged. A moderate load had been pushed right up to the redline. Fortunately, the .45 ACP is a very low pressure round so there was some room to maneuver. Had I tried the same stunt with a .40 the results would not have been quite so benign.

Some bullet profiles will be worse than others in this regard. The truncated cone is particularly bad as are some of the hollowpoints. Round nose bullets are the least objectionable as they feed with the least resistance.

The solution is to limit the number of times you chamber a single cartridge. Most of the ammunition manufacturers recommend that their semi-auto rounds only be chambered a maximum of twice before being fired or discarded. I would suggest that you either rotate the rounds in the magazine so the same cartridge isn’t fed more than twice. Or set aside the ejected unfired round and replace it with a fresh round. Save the unfired round for a practice session when you know you’re going to burn it up.

As not all pistol and ammunition combinations will cause bullet setback, another alternative is to measure the unfired round before you put it back in the magazine. This can be done with a dial caliper or by comparing it with fresh cartridges. Set the round between the two new ones on a level surface. A straight edge set across the two fresh rounds will show if the fed round has shortened. If the bullet has been set back I would recommend you discard the round.

I think it’s a good idea to watch for bullet setback with any autoloader but the .40 is particularly unforgiving.

Maintain your pistol. Replace your recoil spring every 1,000 to 5,000 rounds. Do not swap the factory rate spring for a lighter one unless you’re exclusively shooting light loads. A weak or weakened spring can allow the action to open while the chamber pressures are still high. With the .40, you will probably end up with a blown case.

Keep your pistol clean and properly (lightly) lubricated. A sticky disconnector can allow your piece to fire out of battery. Out of battery fire is not a good thing. Glocks in particular, due to their straight line striker, are susceptible to out of battery fire when not properly maintained. Pay particular attention to the bore and chamber. Fouling- especially leading- in the bore can raise pressures. Material in the chamber may keep the action from closing fully and allow the pistol to fire out of battery. Don’t get lubrication in the chamber or on your cartridges. Lube in the chamber can cause breach pressures to increase tremendously.

When it comes to reloading the .40 my suggestion is don’t. No major firearms manufacturers condone the use of reloads in their pistols. New manufactured generic practice loads are readily available for the .40 and aren’t that expensive. If you absolutely insist on reloading the .40, pay close attention to the warnings- both for the .40 in particular and reloading in general- that you’ll find in all the good loading manuals.

Find out if your barrel fully supports the case. For example, factory Glock barrels do not fully support the case. The unsupported portion of the case will be the first to go when pressures get a bit high. Accurate Arms, Hodgdon and other component manufacturers have gone so far as to recommend that their reloading data not be used in unsupported barrels. If the unsupported portion of the case bulges, the bulge may be ironed out during the resizing process. Unfortunately, that part of the case will now be weakened and subsequent firings with otherwise safe loads may cause a blowout. That’s one reason why I suggest not using brass found at the range. I also suggest not using commercial reloads for the same reason. As careful as the commercial reloaders are, they may not be able to maintain quality control on the incoming fired brass.

Consider using a moderate target load. Paper targets are simply not that hard to stop. By using a lighter target load you can avoid the problems inherent with a high-pressure round. You may need to change to a lighter recoil spring for your practice sessions but I think it’s a worthwhile tradeoff. Just don’t forget to switch back to the heavy spring before firing any full loads.

The .40 Smith and Wesson is an excellent defensive cartridge. I think a .40 caliber Glock is one of the finest defensive pistols you can buy. The .40 is a high performance cartridge and, like any piece of high performance equipment, requires a bit of care and attention in use.