The power factor problem

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:

  1. Reloading
  2. 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.


    1. I was thinking about that, actually. I want to do an experiment with some 110gr .357 loads and see what the reload times/shootability factor is.

  1. I’d think 110gr magnums would be worse than hot 158gr 38s. Based on my experience loading 9mm, at the same power factor, heavier bullets shoot softer. I’m guessing the 110gr 357s would be loaded to a higher power factor too.

    158gr 38s are what the top guys load for SSR, so if you can find a similar factory load that’s the best bet. Of course if you want to shoot matches with a carry load, more power to you.

  2. Factory or reloads?

    If I end up shooting my new to me 66-1 in matches regularly, I’ll probably start loading 158gr berrys with titegroup. That’s what Craig Buckland shoots, and it seems to work well for him. 🙂

    In the near term, I don’t think I’ll shoot SSR in anything but the occasional local match. I have a few hundred rounds of WWB to shoot up before I start loading 38.

    My goal is to make master in SSP before branching out. I haven’t shot the classifier yet this year, but based on match performance, I’m a high sharpshooter or low expert, so I’ve got a ways to go.

  3. It better be fantastic at that price! Best I could find with a quick google was $47.95 per 100, plus shipping.

    I can load the 158gr berrys for about $150/1000.

  4. I shoot primarily 9. I still cut my ammo costs in half by reloading.

    Among the regulars at my local clubs, there’s only one shooter I can think of that shoots at a high level shooting factory ammo. He’s an FFL. There was a second one until recently, but he just started reloading.

    I highly recommend the Hornady LnL.

  5. Speer Lawman Cleanfire 158 +P. Even though it’s rated at 900fps, it’s very soft shooting and keeps your cylinder clean, as well as not smoking up while shooting through a barrel. Sometimes the crimp is a bit loose – chamfered charge holes are a good idea. Back 2 years ago before the ammo insanity you could pick it up for $200 a case.

  6. Okay, I’ll ask the noob question – why is this important? (I ask out of ignorance, not challenge.)

    1. At a club or local match, it’s really not. However, when you get into sanctioned events where money/trophies are on the line, those matches require that your ammo meets a certain power floor. They do this to ensure that no one is shooting super light weight powder puff loads.

  7. I don’t think you should just blow off the rules because its only a “local match”. Chrono or not, you should follow the rules and meet the specified power factor with all ammo. They are still keeping score and someone will be called a winner at the end of the day. Not using the correct power ammo is basically cheating. Please do what’s right, and encourage others to do the same for the integrity of the sport (and yourself).

    1. Adam – don’t think of it as blowing off the rules. I’d rather a shooter came out and shot with .38 Specials that were at a 115 power factor than didn’t come out at all because they were afraid of not making power factor.

      My bottom line is I want more people on the range pulling triggers, and I don’t think that shooting 115 vs a 125 power factor offers enough of a competitive advantage that a newbie shooter with his box of American Eagle LRN is going to beat up on everyone.

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