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Great post courtesy of Gremlin.

Gremlin said:
The trouble with the ACE stuff is that there are too many options, some of which are better than others, some of which are improvements on others, and there is more than one way to do anyting.

First choose the receiver block for the Sig 556

This is going to be EITHER the AR receiver block (#ARRB) (which has a castle nut and STICKS OUT the back of the receiver):




or the AR COMPACT receiver block (#ARRB-C) (this is the BEST OPTION IMHO, because it is flush):



This is a shot of the ARRB-C on a SIG 556 showing how it screws into the receiver flush:



Next choose your folding mechanism.

Your folding mechanism depends on the kind of stock you are using.

If you are using an ACE stock, then choose one of:

a) the regular folding mechanism (#FSM)



or

b) regular folding mechanism with sling swivel (#FSM-SMG)



or

c) the push buton folding mechanism



OTHERWISE If you are using an AR or M4 style stock then choose one of:

a) Folding mechanism with AR interface built in (#FSM-AR):



or

b) Get the CAR15 stock block (aka 'PIG NOSE, #PN) and a castle nut:



and use it to attach your AR15 stock to any of the folding mechanisms:

The regular folding mechanism (#FSM)



The regular folding mechanism with sling swivel



The push buton folding mechanism



Just my opinion, but I think any M4 type stock looks odd with a folding mechanism...
 

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From Ace

This is a reply for Tim with Ace if we are using our stock 556 stock


The parts you will need are, ARRB(Receiver Block) $31.95, FSM(Folding
Mechanism)$59.95, PN(Pig Nose Adapater). This set up will allow you to

use your factory 6 pos. stock and make it fold left or right. If you
have any other questions let me know.
Thanks
Tim
 

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Wonder why ACE does not suggest the ARRB-C that fits flush????
 

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If I want to use a Magpul CTR, have it fold to the left, and want the smallest profile adapter possible, which options should I choose? Am I correct in my assumption that the FSM-AR adapter only allows stocks to fold to the left?
 

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Hey everyone! I have had my Sig for a while...Got all the parts from Ace to do the side folder. Can anyone give me instructions on completing the swap? I am just going to use the 556 stock for now. I could probally figure it out, but someone who has done a few of these would sure be a help to me. I have done most of the normal mods, this will maybe be the last.....yea right! I have enjoyed the forum, lots of knowledge here for sure! :)
 

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I just used my stock Sig stuff for now.....have a CTR ordered from Magpul.I dont care for the extra threaded section showing after putting on the Ace stuff but can be trimmed later.
 

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I've got the compact block and the built in AR Stock interface folding mechanism.

It does fold left only

Looks pretty close to factory if you've ever looked at FAL paras much
 

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Gremlin said:
Wonder why ACE does not suggest the ARRB-C that fits flush????
I don't know, but I have an ARRB-C from them attached to an ACE regular folding mechanism, which is attached to an ACE 7.5 inch stock. I have no issues! I have it set up to fold to the right (towards the ejecting side), and it locks open and locks closed as it is supposed to. In fact, it is just as sturdy as the ACE I have on an Arsenal SAM-7. I even used the CAR plate ACE sent with the ARRB-C.

Prior to buying these parts I called ACE and asked about the stock folding issue. They claimed to not know the details, and re-interated that the ARRB-C was "not recommended for the 556." I'd hade to think those guys at ACE have never tried their ARRB-C on an actual 556, but I can think of no other reason why they wouldn't recommend this part--it actually DOES WORK with the 556!

There is information out there (http://sigforum.com/eve/forums/a/tpc/f/ ... 033041/p/1), that says the stock doesn't fold "correctly" when using the ARRB-C. I don't know for sure what this guy did, but my guess is that he must have tried to screw in the ARRB-C to where it is flush with the rear of the receiver. I did not do that. I screwed it in to a point where 1/16--1/8 of the ARRB-C was sticking out of the receiver. This served two purposes: 1) it allows the CAR plate to mate in perferctly; and, 2) allows enough clearance for the folding mechanism to operate as intended.

So, if you like the stream-line look the ACE ARRB-C provides, do not hesitate to order one. Just do what I did and you will be happy.

Other notes: I can fire the 556 with the stock folded to the right. The controls are hard to get to, and the brass may(?) bounce off the top of the stock, but it can be done.

I'll try to get some pics up at some point, but it may take a while, because the 556 was a last minute pre-Obama purchase that the significant other does not know about--and she would castrate me if she did!
 

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Mounting a Ace folder

I just got an Ace folder for my 556 and am looking at mounting it.. I have never changed stocks on any rifle before. I have mounted the stock to the folding mechanism, and now need to take the old receiver block off, so I can put the new one on. Is there a special wrench that I need to spin off the "guess its called a castle nut" on the back of the gun, or does someone have a trick for that? I can see that the nut is also staked, which should make it more difficult. Does anyone have any suggestions for this part of the install.
 

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You need the special wrench for removing an AR stock.

Places that sell AR parts online should have one.

The staking wasn't a problem - the nut came undone easily.
 

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Re: Mounting a Ace folder

00juice said:
I just got an Ace folder for my 556 and am looking at mounting it.. I have never changed stocks on any rifle before. I have mounted the stock to the folding mechanism, and now need to take the old receiver block off, so I can put the new one on. Is there a special wrench that I need to spin off the "guess its called a castle nut" on the back of the gun, or does someone have a trick for that? I can see that the nut is also staked, which should make it more difficult. Does anyone have any suggestions for this part of the install.
Just got done with the armorer's course. I'd recommend this tool:

http://www.midwayusa.com/eproductpage.e ... mid=367774

As for the staking, it isn't a big deal at all. Just be sure to give it a quick, sharp movement of the wrench. And get a staking punch so that after you reattach the new stock you can restake it and make sure it doesn't come loose on you. Just a sharp tap from the spacer into the castle nut's opening.
 

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For when my sbr stamp comes in on my sig pistol, can I just order one of the folding stock sets specifically for sig 556 from the ace site and have that be all I need?

What tool would I need?
 

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To the people that have done this... can you post some pictures? I want to see if the stock lines up the same way as the stock on with it open and closed. Also post which parts you used. Someone has said with the ACE folder setup the entire stock will sit 1/4" to 1/2" higher than factory....
 

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tibim said:
To the people that have done this... can you post some pictures? I want to see if the stock lines up the same way as the stock on with it open and closed. Also post which parts you used. Someone has said with the ACE folder setup the entire stock will sit 1/4" to 1/2" higher than factory....
Yeah. That was me. Sorry, I didn't take any pictures. I just got my sig folder in the mail yesterday and removed the ace. It was really solid. I just didn't like the way it lined up. That was with the adaptor for the M4 type stock though. Not the pig nose, the other one.
 
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