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Discussion Starter · #3 ·
...FYI...some additional information on parts commonality between the 55x series generally and the semi auto Sig 551-SP specifically and the semi auto Sig 556...




...the 556 is essentially a 551-SP...the semi-auto version of the 551...the method of operation and mechanical function are identical...they differ in that the 556 has a lighter aluminum lower that can utilize NATO STANAG magagines...and the rear of the lower reciever is modified to be compatable with M4 type collapsing stocks...

...virtially all the parts are readily interchangable

...gas block assembly
...gas valve
...gas piston and spring
...gas tube

...the entire bolt carrier group

...bolt and all it's components
...carrier and all it's components
...firing pin and spring
...charging handle
...charging handle catch assembly

...the entire fire control group including springs
...selector assembly
...bolt catch assembly
...pressure point screw assembly
...take down / pivot pins
...bolt cover and hardware

...handguards
...pistol grip

...* the 556 / 551 barrel does not interchange...the rear is treaded differently...likewise the treading for a muzzle attachment differs...

...* the swiss lower will fit and function with the 556 upper...however...when attaching a 556 lower to a swiss upper a small amount of metal must be relieved from the lower portion of the trunion to accomadate the Nato STANAG magazines...

...* the swiss folding stock will not interchange with the collapsing stock...

...* the magazine catch assembly in the 551 differs from that in the 556...and will not interchange...

...* the magazines do not interchange...
 

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SIG operation

I was assuming that the "buffer tube" (receiver extension) meant there was an AR style buffer.

Looking over the schematics, no buffer.

Am I on drugs?

:)
 

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Re: SIG operation

jelarsen1 said:
I was assuming that the "buffer tube" (receiver extension) meant there was an AR style buffer.

Looking over the schematics, no buffer.

Am I on drugs?

:)
The 550/551 don't even have a buffer tube, that is a feature of the 556 only so you wont find it on those schematics.

On the 556 the buffer tube is used merely to mount the stock, and of course make available any number of aftermarket stocks that are available for the ar-15 for use on the 556.
 

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I was needing to look at one of these- Thanks Ullie! Good enough stuff I am printing it now to put into a loose leaf notebook!
:)
 

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Discussion Starter · #9 ·
..possibly some useful information on your 556 concerning the servce life of components....and the need to properly clean...lubricate...inspect and PM your weapon...just for giggles... :lol:


...first off...your 556 is like a machine...any part can fail at any time...although premature part failures are rare...they do occur on any weapon...

...secondly...just like with any weapon...you ought to be on a "preventative maintence" program based on round count...replacing parts as they wear or fatique...each and every part has a "predictable service life" based upon round count...however...you may have a considerable variation in service life depending on the "conditions" under which the weapon is used...for example...for some components such as the barrel...bolt...extractor assembly...gas system and such...hard use will reduce the service life...high pressure and dirty ammunition will also shorten the service life of almost all components including the reciever...proper cleaning and lubrication...especially in critical areas...will have a significant impact on the longevity of the components...


...i would definately keep a set of critical springs on hand...such as the recoil spring...extractor spring...hammer spring...any spring required to operate the weapon that sees hard use...springs fatique and can fail at any time...

...i would also recomend keeping an extra extractor assembly including the pin and an extra bolt handle catch and axle...and possibly the bolt catch assembly...although the weapon will function without it present...possibly a spare firing pin and bolt...and mabey a spare hammer and pin...

...under *hard use*...running the weapon dirty and sometimes dry with lots of rapid fire strings or full auto fire...just to give you a rough idea...

...the bolt has a service life of about 10/15 K...the extractor spring and pin should be replaced at about 5 K...the extractor around 10/15 K

...firing pin and spring ~ 15 K

...bolt handle catch and axel along with spring ~ 10 K

...the barrel is good for at least 15 K...properly cared for in recreational use...probably somewhere around 30 K mabey longer depending on the ammunition...care...and your use...

...the components of the gas system...including the gas valve...gas tube...piston and recoil spring ~ 15 K

...secondary components ~15 K/ indefinately...depending on component.....major components of the FCG ~ 30K

...the trigger housing and reciever...bolt carrier ~ 40 /50 K...

...keeping your weapon "clean" and "properly lubricated" may extend the usuful life of these components...the round count's i've recomended are for weapons that see "service" use...establishing a "practical" parameter of preventive maintence to insure that the weapon will function reliably in the field with an acceptable failure rate...under field conditions using full power NATO standard ammunition...
 

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Uhps.

I feel good having a steel-made SG550.

15K rounds only on a 556? I couldn´t believe that.

Where do you get this information?
 

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Discussion Starter · #11 ·
booster said:
Uhps.

I feel good having a steel-made SG550.

15K rounds only on a 556? I couldn´t believe that.

Where do you get this information?
...booster...perhaps you need to reread my "entire post carefully"...especially this...and i quote...

......"keeping your weapon "clean" and "properly lubricated" may extend the usuful life of these components...the round count's i've recomended are for weapons that see "service" use...establishing a "practical" parameter of preventive maintence to insure that the weapon will function reliably in the field with an acceptable failure rate...under field conditions using full power NATO standard ammunition"...


... my "round counts" are based upon my field experience with the 54x and 55x series of weapons...and i don't see any reason why the 556 can't match them...
 

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ullie said:
......"keeping your weapon "clean" and "properly lubricated" may extend the usuful life of these components

... my "round counts" are based upon my field experience with the 54x and 55x series of weapons...and i don't see any reason why the 556 can't match them...
I agree.
And naturally "we" have no RUAG GP90.

If you ever shoot one of these rounds, you feel the difference.

http://www.ruag.com/ruag/binary?media=186875&open=true
http://www.ruag.com/ruag/binary?media=184464&open=true
 

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Discussion Starter · #14 ·
...FYI...some additional technical information for you...i hope that it provides a little insight on the operating system of your 556...


Posted: Tue Apr 07, 2009 11:25 am Post subject: Carrier Issues

...lately there has been some concern regarding the bolt carrier group (BCG) *hanging* over the hammer...as you "very slowly" bring the BCG fowards while holding onto the charging handle...this ***in itself*** usually will not prevent the weapon from functioning normally...and will *usually* dissapear after you fire and continue firing the weapon...smoothing out the rough surfaces that "many" new weapons may have due to the manufacturing process....this surface roughness induces additional friction into the operating system which "robs the operating system" of some of the energy required to cycle the weapon "optimally"...

...the 556 is a self loading gas driven reciprocating design...as the bullet passes the gas port...the high pressure gases ...following the path of least resistance.... flow through the gas port ( at this very instant only...the gas system is charged with a volume of gas at it's *peak pressure* level...referreed to as "peak port pressure"...which is "not the same" as "peak chamber pressure"...peak port pressure is dependant on the location of the gas port relative to the chamber...any residual "dwell" pressure remaining as the bullet is still traveling through the barrel will be less than the peak"gas port" pressure level "that drives" the operating system...

...the gas then flows through the gas block...through the gas port in the gas valve...through the piston tunnel and into the gas cup of the gas valve...the high pressure gas...exerts "force" on anything containing it...and again follows the path of least resistance...forcing the piston reawards...the only movable component it is pressing against...as the piston moves rewards in it's stroke a very short distance...the gas is vented and is no longer exerting any force upon the piston to drive it rearwards...at this point the operating system is *on it's own*...it "will not be further assisted" in any way...the total energy initially imparted upon it will decrease as the operating system uses this energy to drive itself...either through mechanical disadvantage or doing work...for example...the locking..."unlocking" and camming of the bolt in the carrier... the BCG cocking the hammer against the force of the hammer spring...and again when the BCG pushes the hammer down against the force of the hammer spring as it passes over the hammer...likewise...pushing down the rounds in the magazine while going reawards...and striping a round from the magazine as it comes fowards...further energy is also lost through any "friction" present in the operating system...the bottom line is that the "net (total) energy" to the carrier (the piston is attached to the carrier) must be great enough to over come the resistance of the recoil spring...allowing the BCG to travel rearwards far enough to compress the recoil spring sufficiently...so that the recoil spring becomes "charged" with enough energy to sucessfully pull the BCG fowards with enough force (energy) to push the hammer down against the force of the hammer spring....continue forwards and strip a round from the magazine...chamber it...force the extractor lip over the rim on the case head...allow the bolt to cam in it's track forcing it to rotate and lock into battery...keep in mind that the reward travel of the BCG is "powered" by the energy initially transfered to the carrier by the high pressure gases...the foward travel is "powered" by the energy *stored* in the recoil spring...due to it being compressed...compression springs "store energy" to be later used to perform "work"..in this case to drive the operating system...pulling it fowards...this is a very basic explination of how the system works...there are other factors that will influence the efficicency of the system...such as the "newness of the weapon"...the relative "tightness" of the components" the state of lubrication / type of lubricant...even the tempture of the components...which may have an effect on their dynamic co-efficient of friction (net induced friction) by affecting the demensional relationship with the other components that they have a meachanical relatiionship with...

...with all of this in mind...there are several factors that can contribute...allowing the BCG to "hang" over the hammer while very slowly bringing it fowards...some of which are...a weak or bad recoil spring...which just isn't pulling hard enough as you find "just that right spot" where the hump on the bolt shaft contacts the hammer...allowing the BCG to stop there...another contributing factor could be a very tightly wound hammer spring...or a rough hammer axel...and / or a rough hammer axel tunnel...inducing just enough resistance to prevent the hammer from pivoting freely...there could be a little roughness on the hammer where the hump of the bolt contacts the hammer as it goes fowards...kinda acting like sandpaper...just enough to hold it there...or a combination of these working together...and there are others...as the weapon cycles normally...due to the BCG's velosity...it has a considerable amount of energy...and will simply continue to go fowards...so that this usually is not an issue and will work itself out...as long as it is not a *symptom* of a bad recoil spring ...in which case the spring cannot "store" enough energy to accomplish ***all*** the work that needs to be done to operate the weapon *optimally*...then you may have malfunctions...


...***if this "hanging*** is symptomatic of a "bad / weak recoil spring"...then "no amount" of cycling or firing the weapon will eliminate it...and if the recoil spring is really "bad"...you will certainly have malfunctions..

...a mountain has been made out of a molehill here...this is something i would not be too worried about...just clean and prepare your weapon properly...and use good ammunition and good mags and shoot her...as i have said many times in the past...it's not your place to gunsmith your 556...if you are having malfunctions...and these malfunctions keep occuring after firing a few hundred rounds...and you are using good mags and good ammunition...it's time to let Sig sort it out...

...BTW...there are mags and then there are mags...the market is flooded with many types from many different manufactures...in my opinion there are ***only*** two types out there that can be depended on...especially when you are troubleshooting your weapon...

...any USGI NATO standard magazine with the standard spring and anti-tilt follower (green)...or better yet with the Magpull anti-tile follower installed...an example of currently avaiable mags are the D&H mags...

...the Magpul P mags...even though aftermarket...they work

...i personally wouldn't consider any of the others...including HK mags...Lancers...the SIG mag...none of them...no exceptions...


...i don't feel i've covered this in nearly enough detail...but hopefully i've covered this material well enough to give some of you a slightly better understanding of your 556...and some of the influencing factors that can affect the efficiency of the operating system...in a properly assembled weapon that meets the print specifications...the systems worst enemy is "friction"...that's why it's important to properly lubricate the weapon with a good lubricant...and also to keep her "relatively" clean in the more critical areas...

... http://www.sigarms556.com/viewtopic.php?t=5637
 

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Jamming and sticky block

Thanks for all the great information on this issue posted here. I picked up a 556 ER last week and took it out for the first time on Saturday.

I was very disappointed with all the jamming that I was having. Yes, the bolt would also hang up half way through. I did not realize it at the time but it was hanging up where the hammer/block meet. The first 30 rounds went great, then every other magazine had at least one jam.

After reading all these posts I re-cleaned the weapon, buffed out the bottom of the block where it rubs against the hammer, buffed out the hammer and oiled the rails where the block slides. One other thing I did was to add a bit of silicone (via a cloth) to the rubber seal that the bolt slides through.

Headed back to the range and fired a quick 100 rounds with a variety of magazines both 20's and 30's. No problems what so ever! Thanks for the insight.

I agree with the posts that indicate a manufacture problem with the tolerance of the hammer/block function. I think that Sig needs to be aware of this problem and correct it at the point of manufacture/assembly. If any of you have any pull with them, let them know that this is not an isolated issue. If this had happened to me in a firefight I would be dead, luckily no one at the range was shooting back!
 

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Discussion Starter · #18 ·
Belt Fed said:
the red 3 position corresponds to aiming point black 6 at 300m
What does this mean exactly?
...aiming point "black 6" refers to holding under the target...ie using a 6 o'clock hold...
 

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pappy42 said:
I'm not able to download the 550 armorer manual pdf

Any helpful suggestions would be appreciated
what kind of problem are you having. I just checked and I downloaded it in about 30 seconds..
 
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