The answer to the age-old question of whether or not to top off a magazine to maximize the number of on-board rounds depends on the firearm in question. Even within the same model, individual examples can yield different conclusions.
I just picked up a previously owned SIG Sauer P320 full-size 9 mm to use as a duty gun in my capacity as a reserve police officer in my county. It came with five magazines, and at a good price. When I first shot the pistol, I was quite pleased with the sights, trigger pull and accuracy.
In the police academy, we were taught to load our duty pistols to maximum capacity—referred to as topping off—as a matter of practice and common sense. This included having the magazine full, with a round in the chamber as well.
My problem arose when I loaded my magazines to their 17-round capacity and tried to seat them into the pistol after chambering a cartridge to maximize the gun’s capacity. I had to pound each magazine’s baseplate to get them to stay in the gun, and the two newest ones would not stay locked in place much of the time even with that extra effort. With the other magazines, when they locked in place, the gun would short-cycle after the first round and fail to chamber the next round, consistently moving only partially forward.
In the law enforcement community, our guns have to work first time, every time to stay alive.
What is the problem with this gun? Can it be fixed to make it more reliable, or do I go get my money back and buy something else?
R.K. Tidioute, PA
The SIG Sauer P320 chambered in 9 mm is a solid and reliable-shooting pistol in my experience. That said, while you can get 17 rounds in many of its magazines, there is no space available after the last round has been inserted into the magazine for the ammunition stack to compress sufficiently, enabling the magazine to seat and lock into the magazine well.
The top round in a loaded magazine contacts the bottom of the slide when the slide is forward and the magazine is fully inserted into the magazine well of a semi-automatic pistol. Although there is normally friction on the bottom of the slide from contact with the top cartridge in the magazine, it has minimal effect on the movement of the slide if the ammunition stack can compress slightly back into the magazine body against the magazine spring. If there is no room for the ammunition stack to compress, the friction resistance of the top cartridge in the seated magazine is too great to allow the slide to cycle properly, which causes the phenomenon that you are experiencing with the slide failing to fully cycle.
I would first suggest that you load your magazines to their capacity of 17 rounds, and then apply pressure to the top cartridge with your thumb. The cartridge should move against the magazine spring until it is visibly clear of all contact with the feed lips at the top of the magazine. This small space is necessary for the magazine to seat properly in the magazine well, and also for the gun to cycle properly and shoot reliably.
If you download your magazines to 16 rounds, I suspect your gun will exhibit the reliability you expect from it.
This phenomenon is not only limited to pistols, but should also be considered when loading and topping off any firearm utilizing a spring-loaded, box-type magazine. For example, it is a somewhat common practice to download an AR-15-style rifle magazine (particularly military-surplus magazines) from 30 rounds to 28 rounds to enhance reliability by ensuring the magazine will seat properly in the magazine well and the top rounds in the magazine will flow through the gun without causing any restriction or stoppage.
As always, I would encourage you to voice your concerns to the folks at the SIG Sauer Customer Service department and see what they have to say about the situation you are experiencing. The true complexion of any company can be seen by the actions of its Customer Service personnel to solve a customer’s problems. The manufacturer’s staff is top notch and will undoubtedly help you get to the bottom of the problem you are experiencing.
