Well. I finally got both of my 556's where I  want them.  It's been a long process, with a few disappointments along the way.



Sig 556 Standard
I got one of the first 556 rifles available to dealers courtesy of a friend who works for SigSauer.  It had all the usual problems, canted rail, poor finish, etc.  To Sigs credit they finally replaced the entire rifle with a newer version.  This one has been stellar, eats anything, 1.5 moa accurate, smooth trigger.  The early 556's are a bastard cross between a Sig551 and an AR15, so I figured I'd increase the AR's gene pool on mine.  Definitely not a weapon for the Sig purist.  

The following parts were added or changed:
-Samson STAR556 hand guard/rail system
-Troy Micro Battle sights
-MagPul trigger guard
-MFI 552 style FH
-MFI Swiss style take down pins
-MFI sling
-Vltor Emod stock on a Mil Spec RET
-MI front and rear sling mounts




The Troy sights came from HKparts.net, they have a lower height than standard AR sights allowing a good cheek weld/sight picture.  The Troy Micros also provide an absolute co-wittness with the Trijicon TriPower in it's A.R.M.S. mount.   I would have preferred  the front sight to mount on the gas block like the Samson FFS, but the lower height is more important, and there is plenty of rail space on the Samson rail.  The Samson rail is a great addition if you need to mount lights, grip, etc. to your 556.  It fit perfectly, provides a continuous top rail, and is very solid once installed.  The down side is weight, it adds to an already front heavy weapon.





The MFI rear take down pin doesn't do anything better than the standard pin, but it matches the looks of the Swiss front push pin that allows you to dispense with the original slotted screw type front hinge pin.


Swiss front take down pins.


I used the MFI 552 style 3 prong flash hider, it's an exact copy of the Swiss 552, reduces flash, and looks good to my eyes.


The Magpul trigger guard was a fairly simple modification except you have to enlarge the front hole in the Sig's lower receiver to accept the hex head set screw. I recontoured the top of the trigger guard to match the Sig receiver, then sprayed on a coat of Norrell's Moly Resin in SoCom black.  

The MFI sling is one of the better slings I've used, well made and simple to use.  I have several of them on different weapons, but unfortunately MFI has discontinued them.  All the remaining stock was sold to RobertRTG.com, an HK parts seller.  I don't know if any remain.  

I tried several different butt stocks on the 556 and settled on the Vltor Emod mounted on a quality Mil Spec (BCM) receiver extension tube.  The Emod is slightly longer and provides a better length of pull for me as well as battery storage.  The butt pad is very grippy.  The MI rear sling mount is a personal preference item, allowing multiple sling attachment points.


Sig 556 Classic
My 556 Classic had a few problems, mainly the bolt carrier striking the upper receiver issue.  This was very disappointing after the problems with my first 556.  SigSauers warranty repair solution was to simply grind off the corner of the bolt carriers on customers guns.  So instead of sending it back I did it myself.  Problem solved.  
Material removed.


I decided to make my Classic as close to a Swiss rifle as possible without doing a MarColMar type complete conversion (too rich for my blood).  So the following changes were made:
-Swiss hand guards and butt stock
-Aurora sights
-MarColMar 551 style FH
-MFI sling and hooks
-MFI bayonet lug
-MFI take down pins
-Magpul trigger guard





The reason for the changed furniture is fairly obvious, better ergonomics and the feel of the original Swiss weapon. I was unimpressed with the supplied plastic, the hand guard material seemed brittle and was oddly shaped with vertical encircling ribs, and the collapsing side folding butt stock was loose and wobbly.  The Swiss parts are pricey, but available from Colorado Gun sales.

Probably the biggest disappointment of all the Sig after market parts I've bought are the Aurora sights.  They are somewhat crude in manufacture, considering their cost.  The rear sight turret detents are sloppy and not very positive in their stops.  On my set the rear sight base appears to be a casting that was removed from its mold and finished with a bench grinder.  I remedied these problems by disassembling the rear sight,  polishing and cleaning up the detent stops on the underside of the turret and smoothing/filing the base's casting.  Once again I applied a coat of MolyResin for the exterior finish and filled in the sights adjustment markings with white enamel. The front sight required quite a bit of work with a file and emory cloth to fit the gas block dove tail, and it too received a coat of MolyResin.  

The white dots on the rear sight turret are actually "Glow in the Dark" paint, front sight blade also.  Not tritium, but still usable.  They're very bright after a few seconds of light exposure and last about 15 mins before dimming.

The Aurora's are over priced, but the only option until the MFI Swiss style sights are available.

Once again I used MFI's sling but with MFI sling hooks. The MFI hooks are a copy of HK's hooks and come in (2) sizes, 1" and 1.25".  They attach to the small ring on the gas block, front and rear on the butt stock.





The most difficult mod was installing the Magpul trigger guard in the Classic lower.  The Classic trigger guard is shorter than the standard 556 trigger guard.  This required shortening and reshaping the Magpul to fit.





Also notice in the picture above the MFI Swiss style take down pins.  These pins are captured in the receiver the same as AR pins, but have ends resembling the Swiss pins.  They are R&Red same as AR pins.


MFI on left, standard on right.






The MFI bayonet lug is NATO style and any M16 type bayonet fits.  It was simple to install and appears identical to the Swiss lug that I have.


Finally, the MarColMar 551 type flash hider.  Easy install and gives that "Sig" look rather than an AR A2 FH.  MFI also makes a 551 style FH that is very similar, but open 360 degrees.

 
A2, MarColMar, MFI 551, MFI 552

So that's it.  Two different takes on the same weapon.  My Classic has the look and feel of a Swiss rifle, and the Standard 556 has all the bells and whistles, and the weight to prove it.  It's been a three year process, fun and frustrating at times.  Most of the frustration stems from SigSauers lack of quality control.  The Swiss would never tolerate SigSauer's lax attitude and business practices.  But overall I like both rifles.  It's nice having something besides your garden variety ARs (I have eight).

My "Little Friend"

Very nicely done. Looks like a lot of work, but the end result looks like it was well worth it.

On a side note, you wouldn't have this many problems with an AR.

Great write up. Thanks for posting. Both are great looking 556 rifles.

Could you give some detail about how you disassembled the Aurora rear sight? I find your comments right on target about the Aurora sights. Sure would love to get mine apart and give it a tune up.

C_Swimm-Drive out all the roll pins and remove the circlip at the bottom of the turret for dis assembly.  Take care to not lose the little ball detent and spring.  Polish the bottom of the turret and clean up the ball detents with a drill bit CAREFULLY.  You don't want to enlarge the detents, just make them uniform in size.  Re assembly is a bitch.  Good Luck.

John91498 wrote  "Very nicely done. Looks like a lot of work, but the end result looks like it was well worth it.
On a side note, you wouldn't have this many problems with an AR"

Oh really, I've had problems with many ARs through lack of QC, same as Sig.  Even from top tier manufacturers.