I've noticed on this forum and others that quite a few 556 Classic owners are trying to make their Sigs more closely resemble the Swiss 55x series.  I've done this to my Classic and posted about it in the past.  The process is ongoing.  My plan is to make my Classic as close as possible in looks to the Swiss rifle and still use the AR magazine that I believe superior for a variety of reasons, mostly cost.

The latest change is to replace the standard take down pins with MFI's new pins that have just become available.  I first saw the pins on display @ SHOT.   The pins function exactly the same as the standard pins, but are machined on the ends to resemble the Swiss version.  The pins are machined from tool grade steel and then parkerized a dark black that matches the lower receiver nicely.

MFI pin,  standard pin


MFI inserted


Standard inserted


The MFI pins are machined in exactly the same manner as the Sig pins, with a slot cut the length of the pin to match up with the retaining detent.


The only real difference is the shape of the end of the pin (standard, MFI).


Installation is fairly simple, the front pin is a little tricky (like an AR) but no real problem.

First separate the receivers.


Then insert a magazine or lower receiver block in the magwell and place it in a vise to hold it securely while you remove the front pin detent.  I used a straightened paper clip to relieve the spring pressure on the detent while withdrawing the pin.

(Sorry for the out of focus pic, but you get the idea)

Be careful not to lose the detent pin while withdrawing the take down pin as it's under spring tension.


After applying a lubricant to the new MFI pin insert it in the receiver while keeping the detent flush (collapsed) into the receiver with a small screwdriver.  Push the pin in until it holds back the detent and remove the screwdriver.


The rear pin is easier to install.  Remove the grip screw from inside the lower receiver, pull down on the detent spring and remove the pin.


Insert the new MFI pin and reassemble.  Be careful that the detent spring is straight while tightening the grip screw and doesn't get smashed between the pistol grip and lower receiver.


Reattach the upper and lower receivers and you're good to go.  The whole job took 10 minutes.  The MFI pins don't increase functionality, or any provide any  benefit other than they look more like the Swiss pins.  If that's worth $50.00 a set to you then get them.

My Classic





Another item that MFI sells that I find useful are their HK style sling hooks.  The hooks are cast from aluminum and then powder coated black,  with a spring loaded latch.  They attach positively and won't come off inadvertently.  
The hooks are available in 1" and 1.25" sizes to accommodate most slings. The powder coating appears softer than the parkerized finish on the gas block, and wears off without removing the finish on the weapon.




Now my 556 Classic is almost complete.  All I'm waiting for now are the new MFI diopter/rail sight sets.
MFI diopter rear sight.
MFI diopter front sight

Mike Frost @ MFI tells me they are currently in production and should be available in the next few months.  Anyway, MFI has some neat products for the 556, check out their website.
MFI's website

And no, I'm not an MFI employee, or stand to gain financially from MFI in any way.

Thanks for posting this FD.  Good write-up.

I have the KNS pin in the front right now, and will be looking into these for my 556 SWAT, old style fixed stock.

I'm using Blackhawk's HK style hook on my Vickers Tactical sling to hook to the front gas block, and a Troy bush button Swivel on the Magpul's CTR end.

Blackhawk # 98HM01BK (1.25 Heavy Duty Alligator Claw Hook)
Troy # SMOU-SSQ-00BT-00 ( S.S. Q.D. Swivel)

Great looking rifle!





I too would love a MFI rail/sight, but Aurora's are good for now...

 

snakeman48-These pins are designed as a direct  replacement for the 556 Classic, but the rear pin works fine in the standard 556 (M4 stocked version).  So if you put a original Swiss pin in the front and the MFI pin in the rear they will match.  The MFI front pin won't work as it's to long for the standard 556 lower receiver.

Jerad-The MFI diopter sights will be available soon-hopefully.  When I get a set I'll post up a review ASAP.

Very well done sir. I too want to make my 556 closely resemble the 551, but I like the idea of the railed handguards so I got the SWAT version. Your 556 looks like what SIG USA should have made from the begining. A 551 that takes AR mags and an integrated rail was an improvement too (although the SIG's original execution was flawed). The simple addition of some 551 style furniture, flash hider, and sights make a world of difference.

Whoever at SIG decided to cheap out on the details should be fired. Especially the ER version wiht those fish gill handguards and M4 stock. I am as big a SIG fan as you will find and even I wouldn't consider a 556 (although I had bugged SIGARMS about making a US version of the 550 since 2003) until they introduced the classic series. One I verified that their crappy adjustable side folder could be swapped for a 550 sotck I bought the first one I saw in a shop.

C'mon SIG get with a US company like Mag-pul or such to make you a quality US made 551 stock and handguards for the 556, and then contract with Aurora to supply the sights and ditch that god aweful factory diopter set. Get SIG back the reputaiton they worked so many years to earn.  

C_Swimm:

What is so terrible about the Classic stock?  I really like the fact that it is adjustable, and while I am sure it is not as solid as the original SIG stock it is a lot better than your typical M4 stock.

I don't totally hate the classic stock. I do like it better than the M4 style on the 556. I just like the 550 stock so much better.  I rather wish SIG would have made either stock optional. I have the classic stock on my 522 still, and will probably leave it on there since my 11yr old daughter likes shooting the 552 and with stock collapsed it fits her very well.

I don't like how clunky the classic stock looks compared to the original, but I think it looks much better than the M4 stlye did on the 556. I guess you can't have one that adjusts though and not be somewhat clunkier looking than the original, and it 's going to be looser feeling too just by the fact that it has moving parts.They have to have some play in them or they wouldn't be adjustable.