Ammunition effectiveness in Subcompacts and Compacts

[CDR_Glock]

We have all seen the data from Marshall and Sandow and those experiments on Goats in Europe. However, with the popularity of smaller guns, my question is this:

Are the subcompacts and Compact guns, which have shorter barrels, going to be as effective in penetration and expansion as their counterparts with longer barrels? Or are the subcompact semiautomatics made in such a way that the effective velocity meets the minimum standard for the bullet to perform as manufactured to make that point irrelevant?

[jtg452]

We have all seen the data from Marshall and Sandow and those experiments on Goats in Europe. However, with the popularity of smaller guns, my question is this:

Are the subcompacts and Compact guns, which have shorter barrels, going to be as effective in penetration and expansion as their counterparts with longer barrels? Or are the subcompact semiautomatics made in such a way that the effective velocity meets the minimum standard for the bullet to perform as manufactured to make that point irrelevant?

For the most part, the listed velocities you see on the side of the box are 'hopeful' at best. Many of them are done with test barrels and, in my experience, are significantly higher than what you can actually get from a real gun being fired on the range over a quality chronograph. Some manufacturers, like CorBon, actually test their ammunition in real guns and 'list the real world' velocities rather than the ' 6 inch test barrel' generated numbers.

That being said, you need to look at the design of the JHP bullets that most self defense ammunition utilizes. What is the minimum velocity needed for the bullets to react as designed? THAT'S the $64,000 question.

If you are shooting a bullet that needs to be going 900 to 1,000fps to reliably expand out of a 2 1/4" barrel and you can't get the velocity higher than 700fps from that short a barrel, then don't be surprised if the bullet does not expand as it is designed to.

The problem with shorter barrels is that in many cases the bullet doesn't spend enough TIME in the barrel to generate the requisite velocity. Run through what happens when you pull the trigger, and actually think about it, and it will make sense.

The primer is ignited by the firing pin hitting it, sending a jet of flame into the cartridge and ignites the main powder charge. The powder burns, changing a solid to a gas, and increases the pressure inside the cartridge. The cartridge walls expand until stopped by the much thicker, less malleable steel of the chamber walls, and this loosens the friction based seal (crimp) on the bullet. As the gasses from the burning powder expand, they push the bullet down the barrel. The longer they push, the faster the bullet goes.

That is, until you get to the point where all the powder has burned and the gasses have come to their maximum dispersal and the pressure recedes. At this point, the friction between the barrel and the bullet will slow it down. If the bullet exits before the instant of maximum gas expansion, then you are getting less than optimum velocity. If you are shooting through a revolver, then you lose gasses through the cylinder gap and the velocity will be lower due to it, even if everything else is equal.

That's why the numbers on the back of the ammo box are next to useless in most cases. You can reduce velocity by 50 to 150 fps on average for every inch of barrel length you lose from the REAL WORLD velocities, not the 'test barrel' stuff. When you get down to the first 3 inches of barrel length, you are talking about where you are getting (or losing) the most increase in velocity because the gasses are still building.

How to you adjust for this? The only way I've found is change ammunition. My personal rule of thumb is 'The shorter the barrel, the lighter the bullet' and I'm of the 'slow and heavy' school of thought.

A standard pressure 230gr .45 ACP is not going to see 850-900fps from an Officer's Model and going to a +P 230gr load is just going to increase the muzzle flash due to unburned powder with very little increase in velocity. Why? Because it's not going to be in the barrel long enough to generate the velocity. A 185gr or even a 165gr bullet is gonna have less resistance (both from weight and bearing surface [friction while in the barrel]) and will have a better chance of going fast enough to work as designed.

[kevin mosley]

An excellent question for thought, followed by an excellent reply. Somebody had to add something meaningless here, hence my post.

[wolfhunter]

JTG - the numbers on the back of the box are good for comparing loads form the same manufacturer since they will presumably use the same "fudge factors" on all their ammo. So you could use the box info to start the search for target loads that will "feel" like your PD rounds. At least it's a starting point.

Other than this, I agree whole-heartedly with your comments.

Kevin - I agree with your comment also.v

[Mobuck]

Some ammo makers are producing specific "short barrel" ammo. In addition to giving slightly better velocity from compacts, it is advertised to give lower recoil and muzzle flash. Bullet manufacturers sometimes provide velocity ranges in which their bullets are designed to work best. This information may be available on websites or in reloading manuals.