Open. Flatter?

This is the fifth post in the “flat” series. You might find it useful to check out the previous articles before you dig into this one!

Open division guns add one more rather obvious factor into this whole “flat” equation – the ability to redirect gas from the combustion of the gunpowder to help the gun stay flatter during recoil.

You probably recall from the last article that the movement of the gun in the early phase of recoil directly affects our ability to call shots. Since shot calling is perhaps the most important thing we do as shooters, anything that we can do to make it easier is probably a good thing, as long as we don’t have to make an undesirable tradeoff to get there.

If you watch slow motion video of an open gun in recoil, you’ll notice that they still flip. As compared to a non-Open gun, though, they tend to stay much more stable during the early phase of recoil due to that brief pulse of gas that exits from the compensator and ports just behind the bullet leaving the gun. In some cases, the forces created by the gas are enough to briefly move the gun downward, even.

There’s another effect, too. The use of a compensator also reduces the energy in the slide and barrel combination as they begin to move rearward. Depending on how effective the load and compensator combination are, this effect allows the slide to be lightened, and an even lighter recoil spring to be used. Both of these things reduce overall flip – the spring in the early part, and the lighter slide in the 2nd phase when the slide smacks into the frame.

Check out these two slo-mo videos of two different Open guns, and notice the differences in their movement. Not every Open gun is the same

This would probably be a good time to relate to you how I decided to investigate all this stuff related to biology, as it serves as a good lesson into what I talked about in the last post, about how the red dot sights we use are really pretty marginal, and that we really don’t see significant parts of the gun’s movement.

From time to time, I head up to Brazos Custom to do some shooting. Bob Londrigan prefers to shoot regular semi-rimmed .38 Super in his gun, so when I’m there, I shoot his ammo so that we don’t get Supercomp brass mixed into his Super brass. At one point, when I was there, I’d been struggling with issues calling my shots. I’d put two rounds on a target, call two As, and end up with A/C, or 2 Cs. I figured this was a shooter problem, and I’d been doing a lot of work to improve my shot calling. When I got to Brazos Custom on that particular day, I found out that Bob had changed his load. We’d both been running 4756 in our guns, but Bob had switched over to N105 – a slightly slower, and much more expensive powder. I’d been resisting trying it due to it’s price, in fact, as it’s almost 3 times more expensive than 4756. Well, an interesting thing happened that day. My shots went *exactly* where I’d called them. In fact, it was just that I was calling two As – I was calling them right next to each other on the target, and that’s exactly where they showed up when I went down to paste the targets.

I figured this was just a “trick of the day” – an effect that manifested because I was having to pay more active attention to the gun due to the different timing induced by the change in load. That just further cemented my resolve to work on my shot calling. Time passed, and I went back up to Brazos Custom again to do some work and some shooting. Here’s where it got fun. See, I hadn’t really improved much in the time in between – I was still struggling with shot calling in the same old way. But, Bob was still running the N105 load, and as soon as I put that load back in the gun… BAM. Shot calling dramatically improved. I’m the kind of guy that this led me to question “why?”. Why would changing the load like that improve shot calling? And that kicked all this fun stuff off….

See, the improved gas volume *and* muzzle pressure of N105 allowed the gun to remain more stable during that early, oh-so-important phase of recoil, allowing me to actually see where the gun was as it began to lift, and slowing down the upward motion of the gun during that time. The thing is – the movement of the gun basically looked exactly the same as it did with 4756. What you see behind the open gun, and what appears – to you – to be flat and stable…. may not really be so.

There are a couple of other factors that play into it, too, not just load choice and compensator effectiveness. The size of the dot you pick, and the brightness of that dot both determine how easy it is for the dot to be picked up by the eye. If you’re shooting a C-More scope, you need to also understand that, regardless of what steps you take to try to keep the dot module clean, it will collect dirt, grime, and funk, and will eventually need to be changed. Usually, you’ll see them develop a donut-like shape, or notches in the edge of the dot. At the time time, the dot grows dimmer due to the accumulation of stuff on it’s surface. Lots of folks have tried various different methods to clean dot modules, without much success. Just plan on replacing the module. I do it about once a year.

If you’re having problems following the gun or calling shots with an open gun, try a new dot module and a fresh battery. If that doesn’t work, perhaps try a larger dot size (of course, you trade off precision, but being able to call your shots reliably is most important).

We’ve talked a lot about shot calling, and how a gun that shoots “flat” makes it easier to call shots, but what about the other things that “flat” guns are purportedly capable of providing? That’s up next!

About the author


USPSA Grand Master, NRA Instructor, http://re-gun.com/about/

Permanent link to this article: http://re-gun.com/2012/02/open-flatter/


  1. Rick says:

    Hi Dave

    Great stuff to think about, don’t leave out the use of iron sights and the implications of your findings for shooters in standard/limited. We need to call our shots too.


    Just a thought/question, what lifts the front sight the gases from my barrel or the slide going backwards. I have a sighttracker coming and was wondering if it would be beneficial to my shot calling ability.

    1. DaveRe says:

      Rick, read the other articles in the series :) The only difference between a limited gun and an open gun are the comp and the dot ;)

      The answer is both, and some other stuff, too. But, what you should first ask is what causes the slide to move rearward in the first place – that’s a Newton’s 3rd law reaction to the bullet and powder gasses exiting from the front of the gun. That force pushes against the breechface, and that drives the slide rearward. In turn, the slide compresses the recoil spring as it travels, and recoil spring presses against the frame (well, the guiderod head, really, but that’s tied to the frame for our purposes). And… that pushes against your hand, but from a vector that’s higher than your wrist. Because of the anatomy of the wrist, this force that’s in a vector directed above the wrist causes the wrist to move upward. THAT is what then causes the muzzle to rise.

  2. cb says:

    Did you die?

    1. DaveRe says:

      Uh, no.

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