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Does anyone know if Sig indexes the threads to the same point on the barrels and receivers so you can pull a barrel off one gun and install it on another and have the gas port/headspacing line up reasonablly well.

I know there are other issues to deal with here.....but generally speaking, are the threads indexed?

Tony
 

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I would say yes. Other wise they would have to build every upper receiver and barrel as a matched set. Very costly and time consuming. They have to be able to grab any barrel and any receiver " off the shelf " and assemble it without hand fitting.
 

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Tony,

No the 556 barrel and receiver are not indexed. The Swiss barrels and receivers are indexed; this is for certain. Any Swiss barrel can be installed into any Swiss receiver/trunion and it will headspace. Not so on the 556.


Drop me an email at jsurowitz [at] aol [dot] com
 

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Josh is right-the 556 is not indexed. I believe the gas block roll pin hole locations are drilled after barrel install to time the block to the receiver, so yes they are each a unique assembly.
 

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anhedonic said:
Josh is right-the 556 is not indexed. I believe the gas block roll pin hole locations are drilled after barrel install to time the block to the receiver, so yes they are each a unique assembly.
this is correct.

if you wanted to swap pre-drilled barrels, you'd either need several at your disposal so you can try them until you find one that's close, or...

i suppose you could face off a bit of the trunion, and then cut some spacer washers at a variety of thicknesses so you could time any barrel correctly (like FAL and some galil builds).
 

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...the barrel change out proceedure on the 556 should be the same as that on the 55x series...i've never changed out a barrel on a 556...but have on the 55x...but to not have the barrels index on the 556s...so to speak...would be an inexcusable blunder on the part of Sig Sauer...they should have the manufacturing expertise and technology to hold the appropiate tollerances...

...i'm curious why some of you feel that they won't...what do you base this on...if it's true...changing out a barrel on a 556 would be next to impossible...problematic for sure...and would be a deal breaker for almost all professional endusers...a market Sig Sauer badly wants...

...i'm having a hard time swollowing this...

...just saying...
 

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ullie said:
...the barrel change out proceedure on the 556 should be the same as that on the 55x series...i've never changed out a barrel on a 556...but have on the 55x...but to not have the barrels index on the 556s...so to speak...would be an inexcusable blunder on the part of Sig Sauer...they should have the manufacturing expertise and technology to hold the appropiate tollerances...

...i'm curious why some of you feel that they won't...what do you base this on...if it's true...changing out a barrel on a 556 would be next to impossible...problematic for sure...and would be a deal breaker for almost all professional endusers...a market Sig Sauer badly wants...

...i'm having a hard time swollowing this...

...just saying...
timing the threads on all the barrels, as well as all the receivers, adds an unnecessary level of complexity to both the manufacturing and assembly process.
 

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bullyforyou said:
timing the threads on all the barrels, as well as all the receivers, adds an unnecessary level of complexity to both the manufacturing and assembly process.
...the Swiss have been doing this for decades...as have others..."unnecessary" ???...quite the opposite !...in order to have interchangability of components...especially components that need to be replaced due to wear...such as the barrel in a modern assualt rifle...the proceedure needs to be strightfoward and simple...which it is in the 55x series...the 556 should be no different...the ability to hold the tollerances required in the print specifications during the production phase is well within the ability of a modern facility such as that which Sig Sauer has available...

..anyway...my question was...

ullie said:
...i'm curious why some of you feel that they won't...what do you base this on...
...and still is...what is the basis of your statement...something that was posted on the internet...a small sample of issues some people have had changing out barrels...some vendor's claims....perhaps due to the fact that they can't produce barrels that will index...or do you have a credible contact in the Sig Sauer organization that can confirm this based on the print specifications Sig Sauer is using and their manufacturing protocols...

...like i've mentioned...i've never changed out a barrel on a 556...and i'm curious if this is true or just another internet rumor being parroted over and over again based on one or two individuals having issues with "their" attempt to change out a barrel on a 556 with another "factory" produced barrel...or possibly an aftermarket barrel...


..just asking...
 

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ullie said:
bullyforyou said:
timing the threads on all the barrels, as well as all the receivers, adds an unnecessary level of complexity to both the manufacturing and assembly process.
...the Swiss have been doing this for decades...as have others..."unnecessary" ???...quite the opposite !...in order to have interchangability of components...especially components that need to be replaced due to wear...such as the barrel in a modern assualt rifle...the proceedure needs to be strightfoward and simple...which it is in the 55x series...the 556 should be no different...the ability to hold the tollerances required in the print specifications during the production phase is well within the ability of a modern facility such as that which Sig Sauer has available...

1) the 55X design is over 30 years old now; not something i would call a "modern rifle". many similar arms of that era do NOT have quick-change barrels. the swiss never intended for the barrel swaps to be done by the individual end-user.

2) if the end-user is taken out of the equation, barrel swaps ARE simple. in fact, they are simpler if the barrels aren't indexed.

3) timing threads is more difficult than people typically believe it to be. in the end, depending on thread class and pitch, even working to *tenths* (0.0001") you still can yield mating parts that only time up at ±10, 15, even 20 degrees. indexing ranges like that may not necessarily allow for propper torque. and working to tenths is doable but still a PITA even in modern machine shops.

4) lastly, what the swiss DID, has little bearing on what sig DOES.

..anyway...my question was...

ullie said:
...i'm curious why some of you feel that they won't...what do you base this on...
...and still is...what is the basis of your statement...something that was posted on the internet...a small sample of issues some people have had changing out barrels...some vendor's claims....perhaps due to the fact that they can't produce barrels that will index...or do you have a credible contact in the Sig Sauer organization that can confirm this based on the print specifications Sig Sauer is using and their manufacturing protocals...

...like i've mentioned...i've never changed out a barrel on a 556...and i'm curious if this is true or just another internet rumor being parroted over and over again based on one or two individuals having issues with "their" attempt to change out a barrel on a 556 with another "factory" produced barrel...or possibly an aftermarket barrel...


..just asking...


regarding the rest of your question/comment - i work with several of sig's vendors, i've seen plenty of sigs parts in process, i've seen their prints on certain parts (though i've not studied them), and i have several friends who work for sig, all of whom would be considered "credible contacts".

i've worked on my own barrel, and have not considered the issues anyone else has had, nor do i "parrot" what i've read...

i'm not going to speak for sig. if you really want to know, call them. from my end, i haven't seen anything that would give me reason to believe that the threads are, or even should be, timed. my statement is only my opinion, and in the opinion of a guy in a similar line of work, untimed threads would be quicker to produce, quicker and easier to assemble. hell, there is even a substantial product liability standpoint to be argued when considering end-user serviceability.
 

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bullyforyou said:
1) the 55X design is over 30 years old now; not something i would call a "modern rifle". many similar arms of that era do NOT have quick-change barrels. the swiss never intended for the barrel swaps to be done by the individual end-user.

2) if the end-user is taken out of the equation, barrel swaps ARE simple. in fact, they are simpler if the barrels aren't indexed.

3) timing threads is more difficult than people typically believe it to be. in the end, depending on thread class and pitch, even working to *tenths* (0.0001") you still can yield mating parts that only time up at ±10, 15, even 20 degrees. indexing ranges like that may not necessarily allow for propper torque. and working to tenths is doable but still a PITA even in modern machine shops.

4) lastly, what the swiss DID, has little bearing on what sig DOES.


1. ...i consider the 55x series a modern assualt rifle...along with the FNC/AK5...Colt M4...and a host of others including the AK 100 series...the only difference is that they are just not "modular" like some of the newer breed of assualt rifles...

...the 55x does not...nor was it in the design...to have a quick change barrel...

...the changing out of barrels...even on the 55x series...are done by the end user all the time...all over the world...the people who do these "change outs" are usually referred to as armorers...

2. ...changing out the barrel on a 55x is simple...basically you just screw it in...something you can't do with a pre-drilled/finshed machined barrel that isn't held to the same strict tollerances...put simply...

3...like i said...on the 55x series...you pretty much screw in the barrel...at some point ...about an eight or so turn from indexing it becomes very difficult to turn...then you just torque it in place until properly indexed...done...i do recomend confirming the headspace though...

4....i agree...however...it would be a lot simpler for the armorers if they did...


bullyforyou said:
regarding the rest of your question/comment - i work with several of sig's vendors, i've seen plenty of sigs parts in process, i've seen their prints on certain parts (though i've not studied them), and i have several friends who work for sig, all of whom would be considered "credible contacts".
...so you can't give me a "definative" answer...just your opinion...based on your experience and hearsay...got it...

bullyforyou said:
i'm not going to speak for sig. if you really want to know, call them. from my end, i haven't seen anything that would give me reason to believe that the threads are, or even should be, timed. my statement is only my opinion, and in the opinion of a guy in a similar line of work, untimed threads would be quicker to produce, quicker and easier to assemble. hell, there is even a substantial product liability standpoint to be argued when considering end-user serviceability[


...i'd love to call Sig...but you know as well as i that they won't release this information...BTW...i tried...

bullyforyou said:
anhedonic said:
Josh is right-the 556 is not indexed. I believe the gas block roll pin hole locations are drilled after barrel install to time the block to the receiver, so yes they are each a unique assembly.
this is correct.

if you wanted to swap pre-drilled barrels, you'd either need several at your disposal so you can try them until you find one that's close
bullyforyou said:
my statement is only my opinion
...so now it's only your opinion...not a statement of fact as before...got it...
 

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bullyforyou said:
2) if the end-user is taken out of the equation, barrel swaps ARE simple. in fact, they are simpler if the barrels aren't indexed.



bullyforyou said:
if you wanted to swap pre-drilled barrels, you'd either need several at your disposal so you can try them until you find one that's close, or...

i suppose you could face off a bit of the trunion, and then cut some spacer washers at a variety of thicknesses so you could time any barrel correctly (like FAL and some galil builds).
... :?
 

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i don't believe you are being deliberately obtuse, so i'll just concede the argument and assume i'm having a difficult time conveying the appropriate information.

call sig. ask them. if they won't tell you over the phone, then it wouldn't be something i'd call a friend and ask for - i'd be pissed if any of my friends called and asked me for proprietary company information, especially if they were doing so with the intention of posting said information on the internet.
 

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Re:

Ullie,

I have also changed out a number of Swiss 55x barrels and have all the armorer tools to do so. With regards to the 556, I have only removed a barrel prior to sending it to Frank Hatten at AMA for conversion to a 552 SBR (using a 552-2 parts kit).

In my discussion with Frank, who has undoubtedly done more gunsmithing on the 556 series than any other US gunsmith, the 556 barrel and trunion threads are without a doubt NOT timed. If you don't believe me, just ask Frank. Email me if you want and I can get you Frank's contact info...... jsurowitz [at] aol [dot] com.

I am in full agreement with you regarding Sig's very poor decision in this regard. It is but another in the long saga of how Sig monkey f*d what could have been a fantastic rendition of the 551 made in the US.
 

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Re:

ullie said:
...the barrel change out proceedure on the 556 should be the same as that on the 55x series...i've never changed out a barrel on a 556...but have on the 55x...but to not have the barrels index on the 556s...so to speak...would be an inexcusable blunder on the part of Sig Sauer...they should have the manufacturing expertise and technology to hold the appropiate tollerances...

...i'm curious why some of you feel that they won't...what do you base this on...if it's true...changing out a barrel on a 556 would be next to impossible...problematic for sure...and would be a deal breaker for almost all professional endusers...a market Sig Sauer badly wants...

...i'm having a hard time swollowing this...

...just saying...
...not saying they are or aren't timed...just saying i find it hard to believe...but considering some of the avenues Sig Sauer has taken...it would be just another inexcusable blunder on Sig Sauer's part...IMO...
 

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I worked in manufacturing for 3 decades and my suspicion is that the "non thread timed" barrel solution SIG used for the 556 model is simply due to cost constraints. A thread-timed barrel assembly is certainly more important to a rifle that may need speedy repair in a wartime environment (with a government budget to pay for the convenience), but what advantage does it really provide for a civvie punching holes in paper?

The SIG barrels are nitrided and cold hammer forged, so it is extremely unlikely that a 556 owner will have the time or money to shoot one out (and if so, the new unit can be timed by a gunsmith with relative ease using shims and chamber reamers).

Sounds like some of you wanted a SAN version at a Sauer price...manufacturing shortcuts are understandable and necessary to meet the price point required (unless bankruptcy is your goal). SIG retailed these far below what the original 55X rifles would have cost-and you can't just wish that MSRP into existence, you have to reengineer it to that target.

Just seems there are way more important things to worry about than this issue-unless you are a 556 armorer anyway...
 

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anhedonic said:
Sounds like some of you wanted a SAN version at a Sauer price...manufacturing shortcuts are understandable and necessary to meet the price point required (unless bankruptcy is your goal). SIG retailed these far below what the original 55X rifles would have cost-and you can't just wish that MSRP into existence, you have to reengineer it to that target.
...actually...the LEO/agency price for a Swiss 55x was just around $1100 here in the United States....and that included a Swiss magazine... :wink:
 

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I'm surprised it was that low, but it doesn't change the fact that the current 556 design reduces cost and increases margins.

On top of that, the tooling, etc. for the SAN is paid for by now so to speak, but with the 922R restrictions and possible production capacity limitations, SIG was open to a rethink of the Exeter product-if you are going to have to tool up a separate production line here in the states, one would still likely pursue changes that decrease the manufacturing cost.

Look at LEO vs. Civvie street price on most firearms and you will see the same circumstance-nothing unusual there and the point is really independent of the argument at hand.

Of course all of this is ultimately conjecture-I just like to argue.
 
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