Brass Fetcher Ballistic Testing

The 45 GAP or 45 Glock Automatic Pistol cartridge is a shortened 45 ACP case that functions in handguns that accept 40 S&W and 9mm Luger magazines. This is a fine idea in view of the difficulty that many shooters, including myself, have in getting a firm grip on the larger handguns that utilize double-column 45 ACP magazines. Maintaining a firm, repeatable, grip on a firearm helps to increase your accuracy with a firearm and this will make you a better shot.

I wish that I invented the phrase: “There isn’t any such thing as a free lunch.” But alas and alack, that was Robert Heinlein. You pick up many benefits when you switch to 45 G.A.P but you lose some things as well. To begin, the chamber pressure of the 45 ACP is in the neighborhood of 21,000 PSI while the chamber pressure of the 45 G.A.P is 23,000 PSI. The difference is not enough to write home about so it is fair to assume that the ‘snappiness’ of the round is similar to the 45 ACP which is often described as ‘more of a push than a shove’. This helps reduce the perception of recoil and helps you reacquire the target quickly for a second shot. As we have talked about in other pages on this website, firearm propellant does not directly follow the Ideal Gas law but it follows it notionally. To restate it for convenience (see Equation 1):

Equation 1

We ignore the m and R terms for convenience here. So restated in Equation 2.

Equation 2

Holding the Pressure of the 45 G.A.P as constant, the Volume is decreased by the shorter case of the 45 G.A.P. This means that the Temperature will be lower. The lower the temperature, the smaller the quantity of propellant that can be burned or deflagrated in the same period of time. Now it becomes apparent why Federal Cartridge chose to increase the chamber pressure of the 45 GAP to slightly higher than the 45 ACP, as presented notionally in Equation 3:

Equation 3

As long as the quantity of propellant in the 45 G.A.P is similar to the 45 ACP, then you should get similar terminal performance for a given barrel length.

So what do you give up by shooting a 45 G.A.P? If you are using a sub-compact handgun like the Glock 39 you will experience moderate-heavy recoil. This is not a good ‘first handgun’ but it is an excellent combination if you are an experienced pistol shooter. The ‘loss’ category goes to zero as you move up in size. Using the Glock 38, a compact shooting 45 G.A.P, you will find that the felt recoil is reduced due to the increased surface area presented by the longer backstrap of the grip. Your cost for the increased performance is a capacity of 8 cartridges in a weapon that can hold 15 9mm Luger cartridges.

This caliber is increasingly gaining acceptance in the shooting world as more private gun owners and law enforcement agencies adopt this cartridge. The ‘deficiency’ in magazine capacity might not be an issue for the average shooter, if they ever have to use the firearm. If you are under attack and deadly force is authorized, rare would be the person who benefits from having a fight draw out into a prolonged conflict. You need to be accurate with your shots and determined to win. Only then does the significant terminal effectiveness of the 45 G.A.P come in to play. As always, balance your needs with a realistic threat assessment of your life and environment.

Ammunition selection for this caliber is the same as with the 45 ACP. 185gr JHP bullets or heavier, pushed fast out of the barrel. Expansion out of the short barrel guns and post heavy clothing may be sketchy with some ammunition. Testing should be performed, or reliable terminal ballistics testing information should be sought out before selecting defensive ammunition for your firearm.

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