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Old 02-19-2014, 12:49 AM   #1
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Locating the Center of Gravity (or Mass)?

I’ve been reading quite a few gun forums on the importance of determining the center of gravity (COG) of a firearm. One of the site showed the COG mark on an AR rifle and the reason behind. Some comments I noted included:
1. Having the COG at the rear enables more rapid target acquisition & the ability of firing the weapon with one hand e.g. bull pup configuration;
2. The closer the COG is to the shooter the lighter the weapon feels;
3. The scalloping at the front of the hi-power slide is to save weight thereby bringing the COG a bit farther back;
4. Correlating the COGs of the wearer and the pistol in the holster promotes comfort, safety & freedom from all types of physical activity injury by military & police personnel (from US patent 4898310 - COG holster);
5. Recoil force not in line with the pistol’s COG causing rotational reaction in the pistol as well as a component force moving the pistol backwards (from 1- Holding the Pistol | canadianshooter and http://canadianshooter.files.wordpre...il20moment.jpg)

Well, some may not care at all about its importance. I'm no expert on firearms design but nevertheless I became interested about locating it on my pistol. Factors included were loaded magazine (13 rounds of 115 grain FMJ ammo), pistol in condition 3, and suspended in the air by thin wire (using the “plumb line method”). Unloaded magazine was also used in the process (I know this is immaterial during actual use). Photos showed my “trial and error” proceedings & results.

Loaded Magazine:
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Old 02-19-2014, 12:53 AM   #2
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Locating the Center of Gravity (or Mass)?......continued

Empty Magazine:
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Old 02-19-2014, 12:54 AM   #3
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Locating the Center of Gravity (or Mass)?......continued

From the pictures above, COG location of my HP with loaded magazine is little bit lower than with empty magazine (it’s quite noticeable on both pictures #2 that with empty magazine, the pistol tends to rest almost horizontally than with loaded magazine). Although I don’t have the opportunity yet, COG may or may not change significantly, depending on the ammo (greater than 115 grain ammo, hollow points), readiness mode, grips, frame construction, etc.).
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Old 02-19-2014, 09:31 AM   #4
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I suppose one can work out a weight and balance envelope using moment and arm, like in aircraft. This would take into account the bullet weight of what is loaded in the magazine.
Outside of a discipline like Olympic Free Pistol I'm not sure what benefits, if any, would be.
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Old 02-19-2014, 12:28 PM   #5
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What is overlooked here is that during firing the CG of a pistol, or any firearm for that matter changes. First, the mere action of the moving parts - even the trigger - changes the CG, and that isn't even adding in the outside element of moving fingers, changes in grip strength, etc. Secondly, the total weight of the gun, and its distribution changes as the gun is fired, the bullet leaves the barrel, the case is ejected and a new round moves from the magazine to the chamber.

That all moves the discussion from the realm of the practical to that of the academic.

Having said that, when we speak of how a firearm 'balances', we are really talking about how it 'feels' to us individually. While we use terms such as muzzle heavy, muzzle light balanced, etc, what we are talking about is more a personal sensation than a matter of physics.
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Old 02-20-2014, 11:14 PM   #6
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Quote:
Originally Posted by abninftr View Post
What is overlooked here is that during firing the CG of a pistol, or any firearm for that matter changes. First, the mere action of the moving parts - even the trigger - changes the CG, and that isn't even adding in the outside element of moving fingers, changes in grip strength, etc. Secondly, the total weight of the gun, and its distribution changes as the gun is fired, the bullet leaves the barrel, the case is ejected and a new round moves from the magazine to the chamber.

That all moves the discussion from the realm of the practical to that of the academic.

Having said that, when we speak of how a firearm 'balances', we are really talking about how it 'feels' to us individually. While we use terms such as muzzle heavy, muzzle light balanced, etc, what we are talking about is more a personal sensation than a matter of physics.
Hello mate, I fully agree with you. I stayed out from the dynamic mode of COG on purpose and just simply shared the static side of it. Other members may have different approach and would surely like to learn from them too.

Regards...
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Old 03-03-2014, 11:19 PM   #7
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Locating the Center of Gravity (or Mass)?......continued

I did some updates on locating my pistol’s COG on different modes. Available safety measures were applied. I just posted the pictures showing the combination of line of force for each conditions I made.
1. 12-rounds magazine with slide locked to the rear (thumb safety on takedown notch). I was assuming, to that effect, to mimic the zero point where the slide reaches the rearmost (during recoil after firing bullet #1) and before it goes back to battery.
2. 13+1 round at condition one (Note: As to why the pistol seemed to stay almost horizontal as compared to the previous pic, where pistol is loaded with 12 rounds at condition 3, is beyond my comprehension).
3. 13-rounds with slide locked to the rear
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Old 03-03-2014, 11:28 PM   #8
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Locating the Center of Gravity (or Mass)?......continued

Based on the updates plus the initial results posted, I have marked those observed COG points on the pistol. Please see photo.
Just sharing some comments from different site:
1. "In a polymer-frame pistol, the center of gravity should be almost in the center of the slide which is well above where your hands grip the gun...
In a metal-frame pistol like the 1911 [above] the center of gravity should be slightly below the slide and very close to where your hands grip the gun..."
Gun Review: Kimber Custom II vs. Smith & Wesson M&P Pro 9 | The Truth About Guns
2. "This revolver’s new design not only allows for easier concealability, but lowers the gun’s center of gravity so the recoil felt by the shooter is greatly lessened.." - CHIAPPA RHINO: RE-INVENTING THE REVOLVER
Chiappa Rhino: Re-Inventing The Revolver ? motoHYPE
Attached Images
File Type: jpg FEG PJK9HP CENTER OF GRAVITY POSITIONS.jpg (293.2 KB, 11 views)
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Old 03-04-2014, 01:44 AM   #9
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A totally unrelated but interesting observation here. Your FEG has "KASSNAR LONDON" as the right side slide legend. US imports have variations of Kassnar Bros., KBI etc., and "HARRISBURG PA".
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Old 03-04-2014, 03:12 AM   #10
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Quote:
Originally Posted by abninftr View Post
A totally unrelated but interesting observation here. Your FEG has "KASSNAR LONDON" as the right side slide legend. US imports have variations of Kassnar Bros., KBI etc., and "HARRISBURG PA".
Hello mate!
There is an explanation about the "Kassnar London" roll mark on the right side of the slide. When I bought the pistol early 1993 (no manual was available), I noticed that my pistol markings are different from those FEG write-ups in gun magazine's I had (e.g. the letters FEG inside a polygon on the left side of the slide and the "HARRISBURG PA" on the right side) . So I wrote a letter directly to FEG Budapest requesting to send me the pistol operating manual and an explanation who "Kassnar London" is. A month later I received a letter from Mr. Paul M. Kassnar himself and it contained this explanation (and I quote):

"...I refer to your letter addressed to FEG Budapest concerning their 9mm pistol that you recently purchased.
To answer your questions, these pistols are the same. The difference in the markings occur as the manufacturer has different agents for sales to different countries. Each agent has his own identification system so that he controls the distribution in his market place.
You are correct, KBI is the agent for U.S.A. and Kassnar International Ltd., London is the agent for various other countries around the world.
As per your request we are sending you an instruction and safety manual for this pistol as well as a catalogue sheet. These pistols are distributed in the Philippines by:
ARMS CORPORATION OF THE PHILIPPINES.......
Cordially yours,
(sgd)
Paul M. Kassnar
Director"
(unquote)

P.S. I did receive a manual for model FP9.
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Last edited by pjk9hp; 03-04-2014 at 03:17 AM. Reason: Additional comment.
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