Bore Axis

[BigH]

What exactly is bore axis? In one of my posts I was told that the H&K & SIG's are a bit more difficult to shoot is USPSA & Steel due to a high bore axis. I looked this up and found a couple of blog entries that state high bore axis causes increased muzzle flip. However no one really explains exactly what this is a measurement of. I would have thought that the full length of a USP Expert and its weight, same for a SIG 220 Match or 226 would result in less flip (.40) that lets say a Glock 35 or XD.

Thanks

[Duane Thomas]

The bore is the hole down the center of the barrel. Thus the bore line, or bore axis, is the line down the center of the barrel, i.e. how high the barrel rides above your hand when the gun is in a firing grip. All else being equal, same gun weight, same cartridge, a gun with a high bore axis, like an HK or a SIG, will have more leverage to flip its muzzle on you than a gun with a low bore axis, like a Glock or a 1911. Actually bore axis in my experience is so important that's it's not even a matter of "all else being equal". A heavier gun like an HK will still flip more than a lighter Glock, simply because of its higher bore axis.

[jay.hosford]

Isn't this just the relative hight of the bore over the grip?

[Duane Thomas]

Yes. Or more precisely the relative height of the bore above the web of your hand when the gun is in a firing grip.

[bagdrag]

I've had much better shooters than I tell me that bore axis really isn't that important as long as you can achieve proper timing and consistency from shot to shot. For me however, a low bore axis is a good crutch that helps with lower muzzle flip. Hk's and SiG's definitely have a higher bore axis and I can tell the difference when I shoot them.

[konkapot]

Bruce Gray wrote an article on this very subject; maybe not an article, but rather a posting/thread on........SigForum, I think. As per usual for Bruce, it was logical, well written, and basically concluded that it didn't make all that much difference.

I shot a USP in L10 with moderate success and never noticed bore axis/muzzle flip issues until I picked up a Glock......then it seemed really really obvious.

FY42385

[Duane Thomas]

You mean really, really obvious that you didn't have as much muzzle flip?

[jtielke]

Think of holding a short rod vertically in your hand. Have someone push backwards on the tip of it and think of the amount of torque you'd have to use to keep it from moving. Then imagine if the rod was twice as long. They push backwards on the tip of it with the same amount of force and you'd have to work twice as hard to keep it from moving.

From a purely physics standpoint, the higher the bore axis above your wrist, the larger moment of force you will experience. You have a pivot point near the center of your wrist. Measuring perpendicularly from the bore to that pivot point will give you the lever arm. The length of this arm times the force applied rearward at the center of the bore when the gun is fired will give you your moment of force. Shooting pistols with an identical force and a longer arm will mean you will have to apply more torque to overcome the rotation about your wrist or what becomes upward flip.

Edited July 16, 2009 by jtielke

[bagdrag]

Bruce Gray wrote an article on this very subject; maybe not an article, but rather a posting/thread on........SigForum, I think. As per usual for Bruce, it was logical, well written, and basically concluded that it didn't make all that much difference.

I shot a USP in L10 with moderate success and never noticed bore axis/muzzle flip issues until I picked up a Glock......then it seemed really really obvious.

FY42385

Cool. I think now I remember where I read it from. SiG's have a notoriously high bore axis and Bruce would definitely state it in a logical manner why it wouldn't matter. I don't know though. A lower bore axis just reduces the variable of muzzle flip IMO. Of course there are plenty of talented shooters that are successful with SiG's, so again maybe it doesn't matter. It will be interesting to see how far Max Michel takes that platform. I do wonder though, if a properly tuned comp will make low bore axis a moot point.