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Old September 23, 2018, 01:35 PM   #1
Grant 14
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Position of compensater

I am re-installing a compensater on an old 7 Mag and didnt mark it when I removed. It has two slots that cover about 180 degrees and I am assuming that they face up to help prevent barrel rise but I am not sure. It is a really old one. from the REX SHA COL. Anyone help me here? Thanks, Grant.
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Old September 23, 2018, 02:22 PM   #2
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180° would put them on opposite sides of a circle, so they could blow left and right. I'm guessing from the rest of your description than you mean 90°, in which case, yes, typically the center between the vents would be where an iron front sight would be on the barrel and they would vent upward.

A photo would help.
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Old September 23, 2018, 06:37 PM   #3
Grant 14
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They cover about 180 degrees meaning they are both on the same side and are about 1/2 way around the unit. I assume they should vent up to reduce barrel rise, but I wanted to make sure. Thanks. Grant.
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Old September 24, 2018, 09:50 AM   #4
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I think I was envisioning a longitudinal slot, but I think you may be describing slots cut perpendicular to the bore axis. That's the only way I can make sense of the angle. But it doesn't matter whether I can make sense of it or not. There is no orientation except venting upward that would help stabilize the gun for the shooter, so you have that right.
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Old September 24, 2018, 12:51 PM   #5
Grant 14
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Thanks Nick. My Dad built this gun in the 60s and always called it a recoil eliminator. Having shot it a few times I know that eliminator is not an accurate description. The compensator had been off for a while and I just could not remember its position. Problem solved. Thanks. Grant.
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Old September 26, 2018, 04:26 PM   #6
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Yes, recoil reduction, not elimination, is the most a muzzle brake can achieve. Without a brake, once the bullet leaves it is followed by gases and particles equal in mass to the powder charge and because gas is less dense than lead, it accelerates to a velocity faster than the bullet goes, passing it until it slows. That gas and particle jet comprises an impulse rocket pushing to the rear, and the force it adds to recoil is significant when the residual pressure at the muzzle is high and the mass of the powder charge is significant. In some overbore cartridges, the "rocket effect" (also called "after effect") actually produces as much as 60% of the total recoil, exceeding that caused by the bullet.

With a brake, the idea is to vent the high-pressure gas perpendicular to the bore so the pressure that creates the rocket effect is lost just before the bullet clears the muzzle, eliminating it. Some brakes just vent gas in all directions perpendicular to the bore for that reason. Some direct the gas, as yours does, to try to help control the gun's movement. Yours directs it up to mitigate muzzle rise. The clamshell types and their variants direct it along a shallow rearward angle so the rocket effect pulls the gun forward. That's the only type that tries to mitigate bullet-caused rearward momentum. All of them have the problem that venting gas in any direction but forward raises the sound level for the shooter and especially for people around the shooter. You don't want gas directed at your loved ones, as that makes the loudest sound.

The SAAMI recoil formula includes the rocket effect, and you can try out the calculation with your loads to give yourself some insight into the problem. Note that when you download a cartridge, the muzzle pressure becomes lower, reducing rocket effect and causing muzzle brakes to become ineffective, as they have no rocket effect to mitigate.
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Old September 28, 2018, 12:19 PM   #7
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"...they are both on the same side..." Face the holes up.
That's an old, old design that comes from pistol compensators. Gasses are directed up to reduce muzzle jump. Doesn't really apply to a hunting rifle though. So you might want to think about a more modern muzzle brake. Just remember that a brake will increase the muzzle blast and noise for you and anybody in the neighbourhood.
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Old September 28, 2018, 03:44 PM   #8
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It can work on a rifle. Everything just depends on how much muzzle flip there is to tame. On most lighter calibers it isn't much, but some of the heavy African hunting calibers can climb pretty high. How much depends on the cartridge recoil and how high the bore axis is above the support at the shoulder. Magnaporting has been put on rifles for decades because of that. But minimizing rearward recoil just depends on getting the muzzle pressure vented, as I explained above, and that reduces flip at the same time.
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Old September 28, 2018, 05:15 PM   #9
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You time the compensator to counteract barrel deflection. Typically that will put the ports be between 9 and 10 and 3 and 4 o'clock. You dont need to worry about barrel rise if you can keep the left to right moment contained. If rise is also a problem for you then time it more towards 10 and 5 but beyond that it will be less than helpful.

On that rifle, if you're at the range, move away from other shooters because you'll be louder and throwing gasses at them. They will not appreciate it.
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Old September 30, 2018, 09:51 AM   #10
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The OP has an older design with 180° slots all on the same side, if I understand his description correctly, so he is either straight up or straight down (for more flip) or the barrel is being deflected to one side.
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Old September 30, 2018, 10:20 AM   #11
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Quote:
Originally Posted by Unclenick View Post
The OP has an older design with 180° slots all on the same side, if I understand his description correctly, so he is either straight up or straight down (for more flip) or the barrel is being deflected to one side.
Correct, I'd like to see a picture of it so I could give the best advice.
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