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JESS1344

SIG556R GAS PORT SIZES

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DARTH,

   CAN YOU CHECK THE GAS PORTS ON YOUR SIG556R, WHEN YOU HAVE THE CHANCE, AND SEE IF THEY BOTH APPEAR TO BE THE SAME SIZE?

 

   WHEN I WAS DOING AN INFORMATION RECON ON BOTH THE 556 AND THE 556R, PRIOR TO BUYING MY 556R, I CAME ACROSS SOMETHING INTERESTING.

 

   IT SEEMS AS THOUGH A NUMBER OF THE STRAIGHT 556 (CAL.) OWNERS HAVE OBSERVED THAT THEIR GAS PORTS ARE REVERSED, IE, THE BIG ONE IS POSITIONED WHERE THE SMALL ONE SHOULD BE, AND VICE-VERSA.

 

   OBVIOUSLY, IF NOT NOTICED, AND THE GUN IS RUN ON WIDE OPEN THROTTLE, UNKNOWINGLY, DAMAGE COULD WELL RESULT TO COMPONENTS OF THE RECIPROCATING MASS, IN THE LONG TERM.

 

   I JUST GOT MY "R" OUT OF WALMARTS LAYAWAY JAIL YESTERDAY, AND THE FIRST THING I DID, WHEN I GOT IT HOME, WAS TO PULL THE GAS PLUG AND INSPECT THE PORTS.

 

   TO MY MK-1 EYEBALL, THEY APPEAR TO BE THE SAME SIZE.

 

   I DON'T HAVE ANYTHING AROUND HERE TO MEASURE THE PORTS, NOR DO I KNOW WHAT SIZE THEY'RE SUPPOSED TO BE.

 

   THAT ALSO SEEMED TO BE AN ISSUE WITH SOME OF THE 556CAL. GUNS, IE, VARYING PORT SIZES, ACROSS A RANGE OF GUNS.

 

   I HAVE A TXT MSG IN TO A MACHINIST BUD, TO SEE IF HE HAS ANYTHING TO MEASURE THE DIAMETER OF SMALL HOLES, AND AM AWAITING A RESPONSE.

 

   ANYONE WITH DIRECT KNOWLEDGE OR EXPERIENCE WITH THIS IS WELCOME TO CHIME-IN.

 

   THANKS,

   JESS1344

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I read that the ports are nearly identical.  Examination under 10X magnification confirms.  Slight difference.

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I read that the ports are nearly identical.  Examination under 10X magnification confirms.  Slight difference.

DARTH,

   DON'T TAKE THIS WRONG, MY FRIEND, I'M NOT DOUBTING YOUR ESTEEMED WORD, BUT COULD YOU DIRECT ME TOWARD WHERE YOU READ THAT, IF YOU RECALL, PLEASE.

 

   JESS1344

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I don't know where I read it.  I do know I checked mine and they're very close.

 

On the other hand, I still haven't figured out why my 556R is a single shot.  Guess it's going back to Sig.  Be alot easier if they actually fixed problems instead of just throwing "known" fixes at problems and shipping them back.

 

It acts severely undergassed, no matter which setting I use.  Everything seems fine except the gas piston fit in the gas plug is not tight.  Gas port is big and open.  Everything seems to line up as it should.  Action is smooth.  But the bitch will not eject.  At best it stovepipes.  At worst jams the empty back in the chamber.  And it never goes back far enough to pick up a cartridge from the mag.

Edited by Darth Saigus

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Wow, there goes my image of Sig quality.  I thought they were higher end and quite reliable.  Oh well.....

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One of the things I noticed when I had mine was the rails inside the upper receiver were covered in over spray making them like sand paper for the bolt carrier to ride across. Try sanding them and sanding a bit on the rail slots of the bolt carrier. Honestly I feel for you, I gave mine up strait trade for a saiga 223 after it'd been back to sig 3 times. Good luck.

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Mine was a gen1. The gen 2 I shot was much nicer, but it had only had a few rounds through it, so who knows what issues might occur after a couple hundred. The gen1's didn't like to be dirty at all.

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You could try to find a drill bit (or similar object) that just barely slides in and then measure it with dial-calipers or better, a micrometer.

 

It's a nice looking gun. Hope you enjoy it.

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I don't own one but have researched this issue. There are two potential problems

 

- the "emergency" and normal ports are reversed on some of the US models, leading to many 556 US models being set to emergency out of the box. this is easy enough to correct - just run the adjustment valve backwards. HOWEVER...

 

- the Swiss valve side by side with the US valve appears to have distinctly different port sizing.

 

I'll try to find info on the correct port sizes when I have some free time tomorrow.

 

SIG USA should have made a recall on this issue.

 

I really want a 556 Classic some day, perhaps I will find a good used deal on a "dud" rifle one of these days. shouldn't be hard to fix it without getting SIG involved.

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Jess, check out this thread if you have not read it already. Information about port size differences in the US and Swiss valves, as well as port reversal, is covered here: http://www.m4carbine.net/showthread.php?80037-Another-SIG-556-problem-discovered-Gas-valve-ports-reversed

 

You can definitely see here that the valve should have one port almost twice the overall diameter of the other. If the emergency port is the same size as the normal port, then it won't work as intended, and you can assume this is a machining error.

 

The emergency port is there to deliver a huge shot of gas to the piston in order to free up a frozen/stuck action in the field without disassemble/cleaning. It's supposed to be switched back ASAP when the rifle begins cycling normally.

 

Unfortunately I cannot find any information specific to the port sizes of 7.62x39 - one could assume that they MAY be the same, especially considering SIG USA's R&D reputation, but can't verify that positively. If they are different, the 7.62x39 ports are probably larger - 5.56 has much higher operating PSI and therefore requires less gas volume than 7.62x39.

Edited by mancat

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GUYS,

   I DIDN'T THINK I HAD ONE THAT SMALL, BUT I SCROUNGED AROUND AND FOUND A SMALL DRILL BIT THAT MEASURES .0755 (THAT'S SEVENTY-FIVE AND ONE-HALF THOUSANDTHS FOR THE MATHEMATICALLY CHALLENGED, SUCH AS MYSELF).

 

   IT WILL SNUGLY PASS THROUGH ONE PORT BUT WILL STOP WITH THE BUTT-END OF THE SHANK OF THE DRILL JUST BARELY POKING THROUGH THE OTHER (IT'S PROBABLY .075).

 

   PRESUMABLY THERE'S A MINUTE BURR, OR SOMESUCH IN THE TIGHTER ONE, BUT I THINK I'LL REFRAIN FROM RUNNING THE CUTTING END OF THE DRILL THROUGH THAT ONE, FOR NOW.

 

   ANYONE HAVE ANY IDEA WHAT DIAMETER THESE 'X39 PORTS ARE SUPPOSED TO BE, ARE THEY SUPPOSED TO BE, EFFECTIVELY, THE SAME SIZE, OR HOW MUCH DIFFERENCE SHOULD THERE BE BETWEEN THEM?

 

   THANKS,

   JESS1344

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