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Old April 21, 2014, 07:30 PM   #1
eddiejoe333
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Bore axis

How is this measured? I understand a lower bore axis has an effect on felt recoil, but is it measured from the bottom of the slide, bottom of the frame, or what?

Thanks!
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Old April 21, 2014, 08:10 PM   #2
RX-79G
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No one publishes bore axis numbers, but the point of the term is really the vertical distance from the web of the hand up to the bore line. That distance is a lever arm that determines muzzle flip (and felt recoil).
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Old April 21, 2014, 08:11 PM   #3
darkgael
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bore axis

What he said^^.
I believe that the bore axis is the centerline of the bore..... an imaginary line drawn that is equidistant from the sides of the barrel.
Bore axis is usually considered in its relation to the bones of the forearm, specifically the ulna. The closer the line of the axis of the bore is to the axis of the ulna, the lower it is said to be.
In the very precise pistols used in Olympic precision pistol shooting ("free" pistols), the barrel lines up with ulna.
The Chiappa Rhino revolver is an example of a very low bore axis combat gun.
Here is a pic of a free pistol in hand ....not much forearm visible but you ca get the idea....the barrel axis runs into the axis of the forearm.
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Last edited by darkgael; April 21, 2014 at 08:19 PM.
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Old April 21, 2014, 08:19 PM   #4
James K
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AFAIK, the bore axis is the distance from the center of gravity to the center line of the bore. When a gun is fired, the forward movement of the bullet causes the backward movement of the barrel/breech unit. That is not straight back because the other parts of the gun are not on the bore line, but (usually) below it, resulting in the gun pivoting so the muzzle rises. With a handgun, the center of gravity is not only that of the gun, but of the gun/hand unit.

The more of the mass of the gun is directly on the bore line, the less upward recoil there will be and the more the recoil will be straight back. To achieve closer to straight back recoil in rifles, the stock is often designed so more mass is behind the barrel, resulting in the need to move the pistol grip to the bottom of the gun. This, not "shooting from the hip", is the real reason for rifles with pistol grips.

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Old April 21, 2014, 10:15 PM   #5
RX-79G
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Hold the phone, here. There are many factors that affect muzzle flip and felt recoil, and while CG is one of them, it is not what people are talking about with bore axis.

If you take the same gun and change the grip so you hold it lower, it is going to have different muzzle flip, even though the CG didn't change even a little bit.

And on pistols that are introduced with heavier frames than standard, like the steel framed version of the P226 - no one claims that the bore axis was lowered, which they would be falling over themselves to do if that was the accepted definition.
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Old April 21, 2014, 10:26 PM   #6
eddiejoe333
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Ok, I think I get the idea. I have a Smith steel-frame and a Ruger polymer-frame, both in .40 caliber. To me, both have the same felt recoil, in spite of the weight difference. I was told the Ruger has a lower bore-axis. This would seem to explain the similar recoil.

Thanks everyone!
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Old April 21, 2014, 11:14 PM   #7
chris in va
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Plus, muzzle flip and felt recoil are two different animals. A 357 revolver will feel different than a 357 Chiappa Rhino, which pushes straight back into your hand.
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Old April 22, 2014, 05:14 AM   #8
darkgael
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guns

Quote:
a Smith steel-frame and a Ruger polymer-frame,
To which models are you referring?
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Old April 22, 2014, 08:07 PM   #9
eddiejoe333
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I have a 4046 Smith and an SR40 Ruger
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Old April 23, 2014, 04:45 AM   #10
darkgael
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Bore axis

Hard to tell from pix. The Roger may have a slightly lower bore axis.
The difficulty in lowering the axis of the bore in a semi-auto is, of course, the slide. If lined up with the forearm bones, the slide would have no place to go.
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