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So am I under-gassed?


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I never could get the gun to cycle and when I put a bore light inside the barrel, the ports looked clean and symmetrical so i figured it may be the bolt sticking. Got the bolt done by Pauly and it is doin the same thing. Pauly included three port cleaners/gauge wires so I checked the ports without removing the gasblock. It is a 4 port. The .07 wire fits in the front-most port snug and at about a 45 degree angle. I couldn't squeeze it into either of the side ports but it did appear that they aren't blocked. The rear port is not physically covered, but it is pointed directly into the gas block. Are these ports too small? Is the gas block hole too small?

 

(edit for missing comma)

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Edited by Kdog45ak
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Those ports are not necessarily undersized.

 

What ammo?

 

What puck?

 

What gas regulator?

 

What regulator setting?

 

What happens when it doesn't cycle?

 

Has any other work been done at all?

 

Does it cycle high power loads? On which setting?

Edited by Nephilim7
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Those ports are not necessarily undersized.

 

What ammo?

 

What puck?

 

What gas regulator?

 

What regulator setting?

 

What happens when it doesn't cycle?

 

Has any other work been done at all?

 

Does it cycle high power loads? On which setting?

yes, we need more info.....

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The .07 wire fits in the front-most port snug and at about a 45 degree angle. I couldn't squeeze it into either of the side ports but it did appear that they aren't blocked.

 

I want you to be aware that you are not adequately diagnosing your ports until you take off the gas block and properly check. I have a four port build. I did the same check on my ports that you did. It wasn't until I took the gas block off did I come to realize that 2 of the 4 ports were not drilled completely through. Don't be squeamish, take it off and look.

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This was with federal bulk pack. Stock puck and ccs puck. Auto plug at various settings. It wont eject about 90% of the time. It usually smashes the front of the spent case forward jaming it onto the edge of the barrel. No other work done. I'm going to try some higher power stuff tomorrow.

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The .07 wire fits in the front-most port snug and at about a 45 degree angle. I couldn't squeeze it into either of the side ports but it did appear that they aren't blocked.

 

I want you to be aware that you are not adequately diagnosing your ports until you take off the gas block and properly check. I have a four port build. I did the same check on my ports that you did. It wasn't until I took the gas block off did I come to realize that 2 of the 4 ports were not drilled completely through. Don't be squeamish, take it off and look.

 

 

This is good advice. The job is easy.

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I never could get the gun to cycle and when I put a bore light inside the barrel, the ports looked clean and symmetrical so i figured it may be the bolt sticking. Got the bolt done by Pauly and it is doin the same thing. Pauly included three port cleaners/gauge wires so I checked the ports without removing the gasblock. It is a 4 port. The .07 wire fits in the front-most port snug and at about a 45 degree angle. I couldn't squeeze it into either of the side ports but it did appear that they aren't blocked. The rear port is not physically covered, but it is pointed directly into the gas block. Are these ports too small? Is the gas block hole too small?

 

(edit for missing comma)

This thread outlines an easy port obstruction procedure.

Optimal size for a 4-porter is 4 at .077" or so which is where a 5/64th bit lands you.

Also the extractor slot fix is quick easy, and can help a lot.

 

Also, if a weapon has a UTG-brand quad, they've been known to clamp down on the S-12 gas systems and negatively effect cycling.

Additionally, while you're at the gas block, ensure it's not canted. This can cock the carrier slightly causing a minor bind at the beginning of the cycle, and that can cause issues due to the power loss.

 

Something else to watch out for, is if one has a wide optic like an Eotech over the ejection port, shells can bounce off them and right back into the chamber. (look for the shells making nicks on the underside of the optic if that's the case)

There's other things to look for, but that's a good start.

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If all 4 ports are there (drilled), then polish the top of the hammer and get the action smooth. If the bolt is already done by Pauly, that's half the job. There's just enough gas on a factory 4 port/plug to cycle Federal bulk if the action is smooth enough.

 

With mine, bulk ejects around 90-95% of the time, but I'm having problems chambering now (factory 4 port). It sounds similar to the AGP gen3 mag problem that some seem to have. Even high brass/slugs is having the same problem as low brass in the AGP's. I'm going to try things today again with various ammo types and factory mags.

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Ok, I removed the GB and checked the ports. They were all right about .069" and appeared to be unobstructed. I drilled them out to .077" at the same angle. I Put the GB back on and checked the alignment. The GB was canted slightly to the right side pushing the dust cover over to the left slightly (since it is attached by a hinge). This is how it was before I took it apart. I rotated it to be in line with the carrier. The right port is now almost obstructed by the right side of the GB. It appears that the ports may have been drilled a bit too far to the right side of the barrel. I put everything back together and took it to the range. It previously cycled properly about 5% of the time. This time it cycled about 15-20% of the time. The FTE's all were either stovepipes or jamming the front of the case into the back of the barrel. When it did eject, it threw the rounds almost directly forward at about the 1 O'clock approximately 5 feet away. I don't know how to remove the GB completely because I have a steel band silver soldered around the middle of the barrel and the front sight post also silver soldered on the end of the barrel. Any more tips?

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Federal bulk pack? What DRAM is that? If you don't know then tell us the velocity and weight that's printed on the box.

 

TIP: If it's under 3 DRAM you maybe expecting too much from your S-12 without having a bolt profile.

 

FYI: I'm assuming the steel band is the mounting bracket for the Dragunov stock. That steel band and FSB is not silver soldered but glued.

 

Edited: Oops! I just read the first post and see you had the bolt profiled. My point still stands. I have a build with a profile and the it still doesn't shoot anything under 3 DRAM.

Edited by HighPlainsDrifter
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