So you want to shoot competition, but all you have is a Ruger GP-100 with a 4 inch barrel and some speedloaders. You’re not going to go buy a new gun because the GP-100 is your home defense and carry gun, and you’ve decided you want to compete in IDPA with it so that you can gain the benefits of actually having used your carry gun in a simulated stressful environment.
After buying all the necessary gear for your gun, including speedloaders, holsters, a shoot me first vest, you’re left with getting ammo to compete with. You hear a bunch of seasoned shooters talking about “power factor” and throwing numbers around like “125”, or saying stuff like “major” and “minor” – but like I did when I started playing these games, you have no idea what they’re talking about. Power factor is actually pretty straightforward, it’s the weight of your bullet in grains times the muzzle velocity in feet per second divided by 1000 (IDPA doesn’t divide by 1000, but for the sake of typing ease I will here). So that means that if you’re shooting a 125 grain bullet at 1000 fps, your power factor would be “125”. Or take for example the average 158 grain lead round nose .38 Special load, which is moving around 750 fps: that load has a power factor of 118.5 (or 118500 in IDPA parlance).
Since the Ruger GP-100 competes in Stock Service Revolver division, the power factor for that division is 125…and you can immediately begin to see the problem, as a lot (and I mean a lot) of factory .38 Special loads don’t make that power factor. Now, for club level matches or local matches, power factor isn’t a big deal. I’d be shocked if they were using a chronometer at a local fun match, so for those matches you can use whatever blasto-ammo is cheapest from a place like Lucky Gunner or Cheaper than Dirt. The problem arises however when you start getting into sanctioned matches, such as the upcoming IDPA State Championship. These matches will always have a chronograph to make sure people are not running super light loads that don’t meet power factor.
That leaves you with two options:
- Finding ammo that meets power factor
Now, say that hypothetically you’re not allowed to reload because you’ve almost blown the house up three times, that leaves you with finding ammo that makes power factor. Your best bet to do that is to find 158 grain +P defensive ammo, as it’s usually around 850-900 fps. The Aguila ammo pictured, while not marked +P (because it’s pressure rated by CIP and no SAAMI or something) is running at 900 fps, according to an email from their factory rep.
The bottom line though is that you don’t have to worry about power factor if you’re just shooting the local games, but if you’re going to get into sanctioned matches, you’ll need to find ammo that’s running with enough velocity to keep you legal.