I picked my SIG 556 scm model(no flash hider or folding stock, NY state). The rifle shot very well and was getting around 2" groups with normal ball ammo. I will try the 75gr Hornaday tomorrow. I'm sure that will shoot close to an inch. The problems I have are.

1. upper and lower have a bit of play to them like when you have to use a accu wedge in an AR. Is there a way to fix this?

2. The bolt doesn't stay back after the last round is fired with the SIG 10 round mag or my Thermold 30 rounder. With my 30 round OKAY GI mag it works fine( might have happened once I can't remember). How would I go about fixing this? It seems to happen about 30% of the time.

Questions

1. I need tips on where to add the break free. Should I put it over the entire bolt?

2. I want to get the classic swat hand guards, where do I buy them from?

3. What ACOG would be a good fit for mine with a 16.1" barrel?

Congrats on your new purchase, I love mine and I am sure that you will enjoy yours as well.

1. As far as the play between the upper and lower, this is normal for a combat style weapon. If you wish to tighten up the play there are a few options. first you can use an Accuwedge just like you would use in an AR style rifle. You will need to trim some of the rubber to allow it to fit but it is possible and I have seen this done with success on the 556. Second option would be a 3/4" rubber o-ring around the rear lug. The o-ring will sit between the beginning of the lug and the hole for the rear pin. This is what I have used and it is a very easy solution to wanting a bit tighter fit.

2. As far as the bolt issue, it sounds like it may be weak mag springs. Other than that you may want to contact Sig over this issue, they will take care of it and probably will send some new mags.

3. When I clean and lube my 556 I put a coating of oil or TW25 white lubricant on the rails that the bolt travels in and the rails that the carrier travels in. I also put a light coating on the bolt lugs and any are where there is metal to metal contact. You do not want to oil the gas piston system. Especially around the gas control valve. It will make for a crusty mess after you put a few rounds done the tube.

4. You can find the classic handguards on Gunbroker or Top Gun Supply as well as Colorado Gun Sales. They will run around $85 to $95. The Swiss style handguards will fit a little loose on the 556 due to the slightly different dimensions between the Sig 550/551 and the Sig 556 but they will work. Sig Exeter is now offering on there website new "Swiss style" handguards for $86 and are the same ones that are in the picture I posted in your thread regarding the Aimpoint ML2. They are drilled to accept rail segments witch is cool if you want to mount a flash light but do not need all the real estate and weight that the quad rails offer. Just understand that the picture on Sigs site is not representative of what the actual handguards look. Here is a link to them; Handguards

5. Any Acog that is designed to work with the 5.56/.223 should work well.

Thanks for the help. Great advice and answers. I bet the same ACOG for the M4 would be fine for this since its almost the same barrel length.

The bolt hold-open issue may also be related to letting the rifle break in.  If it's still tight, and not quite cycling as easily as it normally will, then it may be moving back forward too soon to catch the follower.  Try shooting it a bit more, and try using other magazines to see if it helps.

After I cleaned it I used break free, it that ok to use? I will try to see if the TW25 is at the gun store. If any one is interested in my brand new Sig Holosight I have it listed in the optics new exchange. I would trade for some 551/556 handguards.

The break free is fine. I have found the TW25 at Midway and other places online but if all you have is break free then your still good to go. Key is to keep a light coating on metal on metal surfaces. Don't over lubricate or it will actually attract debris. If you do order the handguards from Top Gun Supply they also have the TW25. TW25 Grease

Thanks. How about FP-10 I use that on my Kimber pistol is that ok to use?

With help from Sapper I just fixed the loose receiver problem. I found an old accu wedge I had from the old days and cut it down on the top and bottom so it would fit. I just used a razor blade(be careful when doing this).

I'm using Otis dry lub from rainier arms and like ti so far I still need to shoot with it but its very smooth so far and not wet. Kinda smells like smarties though.

My upper/lower receivers had excessive play. No accuwedge or o-ring was going to fix it...I sent it back, and they replaced my lower. Another story for another thread.....

Tb25 is the shiznit.

I am going to test my new accu wedge job today. It is rock solid now except for the handguards.

There is one more option to reduce the play between the upper and lower receiver.

Use a longer grip screw. One that will contact the upper receiver lug. Then trim it to fit the upper so there is no play between the upper and lower.


I've done it to all of mine and it works perfectly, and there is nothing to break off and jam up the inside of your gun.

I bought the sig swiss handguards from SIG.