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Centerfire Rifles - Semiautomatic or Gas Operated Centerfire rifles, carbines and other gas operated rifles.

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  #1  
Old 05-16-2018, 7:34 AM
wilderness medic wilderness medic is offline
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Default Muzzle brakes and back pressure

Do they greatly effect back pressure? I made my SCAR17 featureless. After removing the “flash hider” (muzzle brake) it only locks the bolt back after the last shot 50% of the time now.
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Old 05-16-2018, 7:49 AM
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Only the muzzle fob was removed?
Doesn't matter what's on the muzzle. The gas system is charged by the gas port before the bullet exits the muzzle. Gas is redirected by the brake up and or to the sides.
Some brakes can affect dwell, but that can cause some cycling problems under the right circumstances. More info needed.
Silencers do add gas system (over gassing), but you're not describing that, so...
Something else changed? Ammo or?

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Old 05-16-2018, 8:23 AM
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Ammo?
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Old 05-16-2018, 8:29 AM
wilderness medic wilderness medic is offline
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Just the stock brake from FN was taken off.

Only ever fired ZQI 7.62 out of it.

Literally the only thing that changed was the removal of the brake. All mags are doing it so it isn’t a mag issue. Gas ports are cleared.
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Old 05-16-2018, 8:54 AM
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So put the muzzle brake back on and report back.
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Old 05-16-2018, 8:55 AM
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Quote:
Originally Posted by wilderness medic View Post
Just the stock brake from FN was taken off.

Only ever fired ZQI 7.62 out of it.

Literally the only thing that changed was the removal of the brake. All mags are doing it so it isn’t a mag issue. Gas ports are cleared.
My gas piston rifles have adjustable regulators. If your scar has one, make sure it's in normal setting.
Failure to lock open 50% leads me to think it's gas.
Converting from bb to featureless required more than a fob swap, so that's why I'm thinking gas system.
Something else changed.

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Old 05-16-2018, 8:59 AM
wilderness medic wilderness medic is offline
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Can’t put the brake back on without reinstalling the BB.


All it took to convert to featureless was pinning the stock(5 seconds), removing the brake, and a munkeeboi grip.
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Old 05-16-2018, 9:14 AM
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Also the gas system is only adjustable to two different positions. I have in the regular non-suppressed position.
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Old 05-16-2018, 9:15 AM
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Quote:
Originally Posted by wilderness medic View Post
Can’t put the brake back on without reinstalling the BB.


All it took to convert to featureless was pinning the stock(5 seconds), removing the brake, and a munkeeboi grip.
Understood. Regulator setting?
Normal or silencer modes? 12:00 or other.
Lastly, you can try NATO powered ammo or = it.
Just read it... Thanx
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Old 05-16-2018, 9:18 AM
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So it gags 50% with the reg in the other position? Silencer mode.

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Old 05-16-2018, 9:53 AM
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test with regulator on other position.

if that still doesn't solve it, buy a muzzle brake or borrow one from a friend and test it. if that solves the issue, then i guess you need to buy a brake or compensator instead of leaving the barrel end bare.
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Old 05-16-2018, 10:03 AM
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Regulator is at 12 o clock. Switching it to the other should reduce the gas which sounds like the opposite of what I need.

Kinda confused on the replies.

Reg is set to normal. Non suppressed setting.

Ammo is NATO 7.62

It literally worked with the brake on flawlessly for 3 years until I took it off.


I’m more asking if brakes really do create that big of a difference? Sounds like they don’t, or at least shouldn’t.
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Old 05-16-2018, 10:30 AM
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I believe any muzzle device with a long-ish close-fitting bore can add muzzle velocity to the bullet and also increase back pressure in the barrel.
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Old 05-16-2018, 12:27 PM
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Muzzle brakes are not features.
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Old 05-16-2018, 12:30 PM
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IIRC ZQI isn't NATO powered milspec ammo.
It's in a Wolf/Tula power range.
Spend some money and get some better ammo. Or not.
Troubleshooting sometimes involves trying the opposite of what sounds logical.
So buy/install a cheap brake and milspec ammo and try her again.
Or not. Hope you get it sorted.

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Old 05-16-2018, 9:30 PM
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You keep using the term "flash hider" and "muzzle brake" interchangeably even though they are not the same. If the factory stock muzzle device is indeed a brake, then why change it at all?

And what did you replace it with?
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Old 05-17-2018, 5:42 AM
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I’ve had poor experience with that zqi ammo, to be fair in a bolt gun not a gas gun.

I’d try different ammo.
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Old 05-17-2018, 5:53 AM
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Try some milspec M80 ball ammo. I also have a NIB Surefire SOCOM 7.62 muzzle brake that I'm selling if you need a brake.
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Old 05-17-2018, 5:59 AM
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Your concept of back pressure is commonly stated as being over or under gassed, and it sounds like your ammunition choice was on the light side. I've never tried ZQI Ammo, but I believe it's imported from Turkey and may not be a full NATO spec load. Removing the flash hider may have shortened the dwell time by allowing the bullet to "uncork" sooner. Try some Winchester 7.62x51 NATO white box. You might also check your gas port hole for build up.
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Old 05-17-2018, 6:59 AM
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Quote:
Originally Posted by kcheung2 View Post
You keep using the term "flash hider" and "muzzle brake" interchangeably even though they are not the same. If the factory stock muzzle device is indeed a brake, then why change it at all?

And what did you replace it with?
Because I’d say it’s 80% brake and 20% flash hider. I think technically it’s called a brake by FN but it does meet the description of flash hider since the end has a much wider diameter than the size of the bullet.
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Old 05-17-2018, 7:18 AM
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OP definitely try different ammo, it's the cheapest test, but ZQI is supposed to be full power NATO-spec ammo and it has certainly behaved that way in my experience with it. You may have got a bad batch. I once had a batch of Wolf 223 that caused short-stroking in an AR. Never before, not since. But ZQI is better spec ammo than the cheaoest wolf 223.

Any muzzle device (except suppressors) on a modern infantry weapon will have loose enough tolerance that the gun will be designed shoot without it. If the absence of a muzzle device is actually causing malfs, then the gun has a different problem which needs to be solved.

I suspect your mag catch is the issue or the bolt hold open. To wit: http://www.calguns.net/calgunforum/s....php?t=1298841

and

http://www.calguns.net/calgunforum/s....php?t=1311643

Last edited by God Bless America; 05-17-2018 at 7:26 AM..
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Old 05-17-2018, 8:11 AM
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Quote:
Originally Posted by God Bless America View Post
OP definitely try different ammo, it's the cheapest test, but ZQI is supposed to be full power NATO-spec ammo and it has certainly behaved that way in my experience with it. You may have got a bad batch. I once had a batch of Wolf 223 that caused short-stroking in an AR. Never before, not since. But ZQI is better spec ammo than the cheaoest wolf 223.

Any muzzle device (except suppressors) on a modern infantry weapon will have loose enough tolerance that the gun will be designed shoot without it. If the absence of a muzzle device is actually causing malfs, then the gun has a different problem which needs to be solved.

I suspect your mag catch is the issue or the bolt hold open. To wit: http://www.calguns.net/calgunforum/s....php?t=1298841

and

http://www.calguns.net/calgunforum/s....php?t=1311643
Interesting. Ill check out the stock mag release. I would think it would work better than the Raddlock I just took off but maybe I put it back on a little bit off or something
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