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Old December 26, 2010, 08:36 PM   #1
Boondoggie
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How to SBR my SIG P556

I have received several PM in the last few months regarding SBR’ing a SIG P556 pistol and as such, I am responding by producing this short tutorial as a ‘how to’.

1. Complete ATF Form 1 – This is the absolute first thing you must do before anything else. There are other threads dedicated to how to complete this form, so I will not go into details here.

2. Wait for your stamp – For the purpose of this thread, I will assume that you are in possession of your stamp and can now begin the legal process of building an SBR.

3. Fitting the stock – There are actually several way you can go with this depending on your budget and personal preference.

a. By another SIG 556 Classic and swap out the lower. Essentially you are done; you are now the proud owner of a SIG 556 classic SBR (I’ll get to engraving your upper receiver and what to do with the ‘spare’ SIG 556 now in your possession in a little bit). BTW, this is the only way that I am currently aware of if you are interested in having a ‘Classic’. I believe there were a couple of after markets considering making Classic lowers, but it is really cost prohibitive.

b. Assuming you decide not to go with suggestion ‘a’ above, or that you did and now have a 16” ‘pistol’, either way the following will demonstrate the steps necessary to add a stock to a pistol lower.

i. Unload and clear your gun. Once completed, check it once more. Set the magazines and all ammunition back in the safe, drawer or in another room.

ii. Unload and clear the gun again.

iii. Separate the two halves – If you have the older style ‘pins’ you will need to use two large screw drivers, turning counter clockwise simultaneously. This requires care not to scratch, nick or otherwise damage the screws. If you have this setup, I highly recommend purchasing this. If you have the newer style lower, simply push the two pins from the left side towards the right, similar to any AR.

4. Remove the rear plug – Again several ways to accomplish this.

a. Buy a tool from this guy but remember, you’ll probable use it exactly once, unless you plan on doing more than one. In which case….

b. Make your own tool – again several ways of doing this depending on if you plan on keeping the rear plug or simply want to ‘get it off’. I was merely interested in the latter and hence used the following method.

i. Use some clamp protectors and clamp the lower receiver to a bench vice with the plug pointed up on an angle.

ii. Carefully heat up the plug (I used a MAP gas touch) – caution, SIG uses a plastic plug on the bottom of the sling adaptor just below the plug, stay away from this. The reason for the heat? Again depending on when you purchased your gun and how the plug was installed, either a whole tube of red Loctite was used or none at all. Yeah, SIG was (is?) not known for ‘quality’ on most of the 556 product line.

iii. Heat for 2 – 3 minutes. Did I mention carefully on the plug itself?

iv. Inset large needle nose pliers into the two holes in the plug.

v. Use a set of channel locks to ‘clamp’ the needle nose pliers in place.

vi. Apply even force to the channel locks in a counter clockwise rotation.

vii. Remove plug and discard, done.

c. If you are interested in a ‘less destructive way’, try goggle, there are more ways that I can shake a stick at. Necessity is the mother of all inventions.

5. Install stock – Again, depending on your budget, taste, style, individualism etc… there are several ways to go.

a. Purchase a MIL spec AR baffle tube, screw on and install a stock of your choice – done.

b. For a folding stock, I recommend ACE ltd.

i. this

ii. or this

iii. or this with this.

6. Final step – Engrave your upper receiver. Since you are now the ‘manufacture’ of your new toy, you must have your name, city and state engraved on the upper receiver as per ATF. (unlike an AR, the upper receiver is the 'registered' portion on a SIG) Here is a good link regarding engraving.

Done.

I hope you have found this useful and as usual, I assume no responsibility, risks or liabilities. This is mealy for educational purpose only.
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Old December 26, 2010, 10:34 PM   #2
Willie Lowman
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Why did you wait till last to do the engraving? It takes months to get the tax stamp from the ATF, that is a great time to get the engraving done.
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Old December 27, 2010, 09:23 AM   #3
Boondoggie
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No particularly reason.

The engrave I use does a lot of work for the tool and die industry, is local to me and takes less then 3 days to complete, so it isn’t a top priority in the order of scheme.

Besides, what’s the rush? I think I've discovered why NFA items are so addicting, for me anyways. Once you finish it, and have had a chance to shoot it, fondle it, sleep with it (yeah too much information), it’s an anti climax. You want that ‘thrill of the chase’ feeling, so you began another and another and another…….

Last edited by Boondoggie; December 27, 2010 at 09:37 AM.
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Old December 27, 2010, 09:09 PM   #4
Ridge_Runner_5
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Quote:
Why did you wait till last to do the engraving? It takes months to get the tax stamp from the ATF, that is a great time to get the engraving done.
If it gets denied for some reason, then you have a standard, nothing special receiver that you have indelibly etched in with your private information.
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Old December 27, 2010, 11:59 PM   #5
Willie Lowman
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Come on now. If you think there is something lurking in your past that the ATF would turn you down on a form 1, just forget about it.

I don't have that problem so I can't see the harm in getting my info engraved on a gun whilst the examiners are licking my tax stamp.
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Old December 28, 2010, 03:14 PM   #6
Boondoggie
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Quote:
Come on now. If you think there is something lurking in your past that the ATF would turn you down on a form 1, just forget about it.

I don't have that problem so I can't see the harm in getting my info engraved on a gun whilst the examiners are licking my tax stamp.
I would agree, however, I also see Ridge’s point. Assuming this is someone’s first NFA, I would be inclined to agree. Not necessary that there maybe something ‘bad’ in one’s background, but for that simple ‘uncertainty’ factor.
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Old December 29, 2010, 03:48 PM   #7
nrtnburgess
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Thanks for info..but why seperate the uper and lower can you not just remove plug..I am new to the black guns and wanting to learn all I can
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Old December 29, 2010, 03:53 PM   #8
nrtnburgess
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Also what about forends for a p556 sig says that they are the only peolpe who make a forend for this gun and it is the swat quad rail and is 259 plus shipping to them because only there gun smiths can change them out any info would be a great help....also what is the diff on ATF form 1 and form 4
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Old December 29, 2010, 04:21 PM   #9
Willie Lowman
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I don't know what you are asking in the first half of your post. Spelling, punctuation and clarity are important.


A form 1 is the form you fill out to make a NFA item (except machine guns, we can't do that any more. )

A form 4 is the form you fill out to transfer ownership of a NFA item.
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Old December 29, 2010, 06:42 PM   #10
Boondoggie
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Quote:
Thanks for info..but why seperate the uper and lower can you not just remove plug..I am new to the black guns and wanting to learn all I can
Why separate into two halves? Why wouldn’t you? It makes it much easier to work with as you don’t have the length of the barrel and or the width of the forearms to contend with. It’s also a preventative action on your part, you don’t want to accidentally scratch, ding or other damage your upper receiver. Remember, on the SIG this is the registered portion, in other words its means a new gun if damaged beyond repair.

As for a quad rail, the one I would recommend is this.
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Old December 30, 2010, 09:44 AM   #11
nrtnburgess
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Thanks sorry about the spelling. As for the quad rail in the link you gave it has a option for one with the flange and with out...what are they talking about ?

The factory rail i have connects to the lower with 2 set screws that it pivits on this rail looks like it mounts a differeny way is it for the classic ?
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Old December 30, 2010, 01:34 PM   #12
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The ‘flange’ is this



The stock rail disassembles in the following way

1. Unload and clear the gun.

2. Separate the two halves by pushing out the ‘take down pins’.

3. Push down on the charging handle latch and remove the charging handle.



4. Remove the BCG from the rear of the upper receiver.

5. Depress the gas plug detent and rotate the gas plug until the top and bottom tabs line up with the cutout on the gas tube.



6. Remove the gas plug and piston assembly.

7. Using the folding stock lock tab, push down on the bottom half of the quad rail.



8. Separate the top and bottom quad rail by lift up at the rear and pulling out.



Note – you can either remove the gas tube or leave it in place, the stock rails will disassemble either way. In the pictures I have it unlocked as I was in the process of cleaning. Yes, even gas piston guns needs to be cleaned

The Samson rail installs by removing your stock hand guards and the top rail mounted on the receiver. The top rail of the Samson is then installed in it’s place and the bottom secured to the top.
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Old December 31, 2010, 10:08 PM   #13
nrtnburgess
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cool thanks for all the info i am going to a show tomorrow to look for a buffer and a rail oh and are the threads on the non swat edition sig p556 comercial or mil spec dont wanna buy a mil spec and it not thread into the pistol
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Old January 1, 2011, 10:23 AM   #14
nrtnburgess
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Oh and also should I get one with the flange or with out are there any advantages or disadvantages thanks
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Old January 1, 2011, 12:17 PM   #15
Boondoggie
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If you are referring to the baffle tube threads, there is no difference between a MIL spec and a commercial, both will fit. The difference is in the OD of the tube itself. In other words, a commercial collapsible stock will not fit correctly on a MIL spec tube and visa versa.

I don’t believe there is an ‘advantage’ to the flange, purely cosmetic.

Again, be sure you have your tax stamp before attempting this conversion. I can not stress this enough.
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Old January 1, 2011, 05:50 PM   #16
nrtnburgess
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got ya yup not doing it until i have paper work ...but will i need to retain the factory ring thats behind the pug to in stead on a regular ring this one looks like it has to fit on the round nip. under pug and i was told there is a spring under it that keeps pressure on the pin that hold the up and low together
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Old January 2, 2011, 11:03 AM   #17
nrtnburgess
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well i traded my gun think i am gonna get a lwrc rhey already have everything i want thanks for all your help i am sure i will prob have more questions in the future with what ever i get cause i am new to it all
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Old January 3, 2011, 12:17 AM   #18
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This is what it looks like when your done.. My 5 year old hitting a man size target at 100 yards everytime he pulls the trigger.
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