Swiss SIG 553 pistols have hit the US market

[hotrodder636]

Thanks for this, been looking for a good parts supplier.

With that said, does anyone know who has a Sig 55x folding stock ‘in stock’?

Gatewood supply is your best bet for SIG spares.

[68ar15]

Thanks Josh. I compared the 4-position one that came with my 553RP with the one that came with my 556 SBR. While they will interchange in either rifle, the inside diameter of the 553RP's 4-position valve is smaller than that of the 556 SBR's valve. As a result, the 556 SBR's piston will not fit inside the cup of the 553RP's. I did notice that the 553RP's valve is marked 12, 13, 14, 15. I'm guessing that these numbers represent the diameter. The 4-position that JDI is selling on their website are marked X, 0.9, 1.2, 1.3. I'm assuming those are small diameter holes meant for 5.56x45 rifles. All this has me wondering if the valve cup sizes are different in order to prevent putting a 7.62x39 valve with the larger holes in a 5.56x45 rifle. Assuming you have one, would you mind measuring the inside diameter of the cup of your 4-position 5.56x45 valve? My 556 SBR runs like a champ, but it's obviously overgassed. I'd like to fix that.

552 and 553 pistons are smaller than 550 551 and 556

Gas ports are available in a wide variety of sizes based on caliber model and ammo. There is a chart on JDIs Facebook

[PGT]

Has anybody swapped real Swiss diopter drums into an MFI repro housing?

[Bret]

552 and 553 pistons are smaller than 550 551 and 556

Smaller in diameter at the head? Would a 551 gas valve work in a US made 556?

Gas ports are available in a wide variety of sizes based on caliber model and ammo. There is a chart on JDIs Facebook

Can you provide a link please? I tried using my wife's Facebook to find it, but no luck.

[sigswiss]

Smaller in diameter at the head? Would a 551 gas valve work in a US made 556?

Can you provide a link please? I tried using my wife's Facebook to find it, but no luck.

Gas valves on 553 (5.56x45) and 553RP I.D. are both .512" (13mm) and same O.D. of .665" (16.90mm).
Gas valve on US 556 Classic I.D. is .553" (14.03mm) with O.D. of .663" (16.83mm).
My mic isn't perfect so +/- ~.005". Sorry, no 550 or 551 data at this time.

Interestingly enough, the I.D. of the 751 SAPR was an exact match with the 556 Classic @ .553" (14.03mm), but the O.D. was ~ the same as the 553 and 553RP - .665" (16.92mm)

At this point, with the I.D. a perfect match, and the O.D only about .1mm difference between the 751 gas valve and the 556 Classic, I had to try putting the 751 valve in the 556. The O.D. fit, but the lower "male" wing on the 751 valve was just too wide for the 556 gas tube flange -about 1.5mm.

A 751 gas valve should be obtainable, but determining what the gas orifices should be would be the trick.
I believe that Dave said that when you ordered a gas valve, to give him the # from the chart below and he could drill it.
It would still require machining on either the valve lower "wing" or the gas tube flange.

It's really a shame we can't buy gas valves for the 556 from Ron Cohen by the handful for $20.00 -or could we? I like the "up" on the gas valve as opposed to the actual size of the orifice!



Don't know where the original link is (somewhere on his facebook page), but here is a copy.

4 position gas valve.jpg

[PGT]

I bought two spare 556 gas regulators from OpticsPlanet to send off to get drilled. Took forever but they eventually shipped.

[Bret]

For $29 I'll get one to play with. Did it arrive undrilled? The picture shows different size holes, but both of mine (556 SBR) are almost exactly the same.

[PGT]

I haven't opened the bags to be honest. I'll check them out tomorrow.

[Bret]

If you can measure the size of the holes, that would be very helpful.

[scubadds]

I have a 4 position gas in my 553 and I have run it with a can. Ordered it from an overseas company with a lot of research. Took 6-7 months to get. I did order a spare