smoke in my eye

[vinconco]

I built a PCC a few years back using a New Frontier upper (side charge), lower, barrel and bolt.  It has a ton of ammo through it but I'm experiencing something new.  I'm getting gas blowback in my right eye (shooting right hand).   I had the barrel recut for a deeper chamber, plunk tested the ammo, cleaned the bolt and barrel and I'm still getting gas back in my eye.  I'm shooting 124 FMJ TC @ 1190 fps using federal 100's and IMR4756  (because I have a ton of it and shot it for years in a 38 super)  COAL 1.125"

Any one else have this problem?   I tried searching but the search terms bring up too much unrelated stuff.

Edited April 23, 2019 by vinconco
correct COAL

[ChuckS]

The NFA side charger upper has a little door that allows the bolt to be removed by providing clearance for the "gas key". It is spring loaded so it will stay up unless you push it down when seating the rear of the upper in the lower. Make sure it is closed or you will get the puff of gas you describe...

[vinconco]

The door is closed and I even put tape over it to test it.

Then I put tape across the back of the upper extending past the right hand side to see if that would stop the gas... and it did.  This means the gas is coming from around the bolt.     

[Bwillis]

..

Edited April 23, 2019 by Bwillis

[Roy T]

Is this not a side charger? will the handle just be to stop the puff?

[AHI]

What buffer system? Sounds like your bolt is opening to soon .

May be time for some new springs.

[vinconco]

1 hour ago, AHI said:

What buffer system? Sounds like your bolt is opening to soon .

May be time for some new springs.

It's the Taccom buffer system

[Screaminyz]

What buffer system? Sounds like your bolt is opening to soon .
May be time for some new springs.

Like AHI said maybe try putting a new buffer spring in as you also mentioned the rifle had a ton of rounds through it and maybe not holding the bolt completely shut long enough.


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[rowdyb]

It's called "blow back" for a reason....

[lstange]

12 hours ago, Screaminyz said:

try putting a new buffer spring in as you also mentioned the rifle had a ton of rounds through it and maybe not holding the bolt completely shut long enough.

 

I don't think buffer spring makes any perceptible difference in how fast the bolt opens in open-bolt designs. The spring is too weak compared to the force that acts on the bolt face during firing. Back of the envelope: 200 MPa * 3.14 * (9 mm / 2)^2, or about 1.3 tons of force. The purpose of the spring is to slow down the bolt after it started moving, not to keep it closed.

 

To keep the bolt closed longer, you need to make the bolt  (or the buffer) heavier.

[Startingover]

5 hours ago, lstange said:

I don't think buffer spring makes any perceptible difference in how fast the bolt opens in open-bolt designs. The spring is too weak compared to the force that acts on the bolt face during firing. Back of the envelope: 200 MPa * 3.14 * (9 mm / 2)^2, or about 1.3 tons of force. The purpose of the spring is to slow down the bolt after it started moving, not to keep it closed.

 

To keep the bolt closed longer, you need to make the bolt  (or the buffer) heavier.

The problem with this theory is that he said it's just started.

Not that it has always done it, so something has had to of changed.

Edited April 23, 2019 by Startingover

[vinconco]

I figured it out !...

I had a KAW Linear muzzle device on it that was obviously creating back pressure.  I didn't notice it much when I first built the PCC but maybe it got worse as it fouled up.

Took it off and problem solved.

Now I need something that won't create back pressure to cover the barrel threads.  IS there such a thing as a "Comp" that works with 9mm pressures?

 

 

 

 

 

[DKorn]

1 hour ago, vinconco said:

I figured it out !...

I had a KAW Linear muzzle device on it that was obviously creating back pressure.  I didn't notice it much when I first built the PCC but maybe it got worse as it fouled up.

Took it off and problem solved.

Now I need something that won't create back pressure to cover the barrel threads.  IS there such a thing as a "Comp" that works with 9mm pressures?

 

 

 

 

 

 

Throw your favorite 9mm comp on there, but don’t expect much change in dot movement. I’d personally go for the loudest comp I could find to help the timer pick up the shots more easily. 

[Startingover]

Vg6 Gamma