Not sure if this should go here. Mods feel free to move if you need to.

I haven't seen many reviews except for the ones from SHOT show. So heres mine.

Just picked up my Sig 556XI Friday and spent a few days messing with it and shooting before doing a write up. This is my first Sig rifle and first gas piston gun.

Out of the box: Very impressed. Very lightweight and easy to handle/move around. The polymer forearm and grip are slightly stippled from the factory and provide a very positive grip. Action is very smooth and the Ambi charging handle is very well done. I set mine up on the left side as a right handed shooter and it is a very nice improvement over other Sigs I've handled. The forearm does move slightly, but nothing to really complain about. The top rail on the receiver is machined into the forearm that covers the piston and bolts on the top with 3 screws that are secured with thread locker. Very solid with no play, even after removal. The gas system selector moves freely and is easy to adjust. The trigger is a factory 2 stage. It took some getting used to from my AR, but at the range I loved it.

Barrel is a 16" 1/7 lightweight barrel. It did get warm rather quickly. But had decent cooling.

The factory sights are nice, very well made. They look like oversized Troy sights and are standard AR height sights. In my opinion, they look horrible. Way oversized. But I will give Sig credit for including a good set of irons when so many others don't.

The stock is the standard Swiss folder stock. They added a removable check riser and it is a very nice addition. For the factory sights, you almost have to use it to get a good cheek weld with the stock. I used it at the range with Magpul BUIS and it worked very well. It snaps tight onto the stock and is slightly difficult to remove. Very solid with no wobble/play.

My only complaint (and this seems to be normal for Sig) is that there is some play between the upper and lower. Its not horrible, but it is there. Also, the selector is somewhat hard to reach. I have large hands and struggle to get to it quickly. Someone with smaller hands may want to consider that.

Range report: Took it to my local indoor range for a test run. I did not use the factory steel mag. Very disappointed in the quality of the mag. It was very scratched and beat up from the factory.

I loaded up (4) 30 round Pmags (Gen2 and 3) and a 20 round Gen3 Pmag. They all fit in the magwell without issue. There is some slight play in the magwell, but that is to be expected (to me anyway) since it is supposed to work with all AR mags.

I shot 140 rounds total and only had one Failure to Feed. I believe it was mag related as they were brand new mags that I loaded with a speed loader. It put the nose of the round into the face of the barrel. Other than that it was flawless. Very soft recoil and I was able to follow up shots very fast. Mag release it well placed and easy to use. It is a little stiff but I am sure it will loosen up some with use.

If you are a reloader, this rifle destroys brass. It puts a good dent in the side/neck of the casing. It also crushed the top of the casing where the bullet is. I don't reload so I don't know how much this ruins brass.

One other thing I want to mention is that the rifle is covered in factory Sig grease. I recommend cleaning it off before shooting as it gets EVERYWHERE inside the rifle. Made cleaning very difficult.

I think I covered everything. If there is anything you want to know just ask and I will do my best. Thanks for reading!

Pics to come ASAP.

Thanks, have a 556R but I'm considering the xi.

Im very happy with this rifle. Ive never been one to jump on the new gun bandwagon, but for this one I am glad I did.

Pics:












Here is the target from 25 yards standing, not supported. Shot as fast as I could follow up. This was using new out of the box Magpul BUIS that were zeroed from 100yds

Nice report! Have you weighed it yet? If so, can you tell us how much it weighs?

I will when I get home. I'll compare it to my AR

Thanks for the review.  Mine should be here Monday.  Can't wait to check it out.

Would you mind posting a few photos with the handguard removed, detailing the barrel nut?

That gun is super ugly but I want it .

Thanks for the review.

Here ya go. Not the best, crappy camera







Gas block is fixed to the barrel.

I thought the same when I saw it. It looks a lot better in person.

Looking forward to handling one...........soon as I find a shop that has one

where in Georgia are you located? I could be local to you

Would it be possible to get a photo of the gas valve by itself?

A lot of us are wondering if it is cross compatible with the older 556 classic and perhaps seeing it would let us have a better idea.

The uppers are supposed to be swappable with the older lowers. And I'm not sure what part you mean. Like the piston or remove the top rail and get a better pic of the block?

The little valve switch on the front of the gas block. It is supposed to rotate between three positions (normal, fouled and suppressed). If it is anything like the 556 classic you depress a little detent pin and it should rotate about 90 degrees and pop out. When it is out in your hand it looks like a little sink drain stopper but with tiny gas holes in the tube section.

These are 55X gas valves:



There were rumors early on that this gas valve would be backward compatible with the older 556 classic line, enabling us users of the classics to get a factory three position valve for our guns. Then I kept hearing rumors that the XI used a different sized piston similar to their 516 platform which would make the valve incompatible with the older 556 classic.

Gotcha. I'll snap a few pictures when I get home from work tonight.

Thanks for the report-  I hate the looks of the stock and short handguard

Nice review.  The safety looks the same as the 556 classic.  Krebs Customs makes a replacement safety lever that is very easy to switch.  Tap out a roll pin, lay the extended safety on and put the pin back in.  Made a world of difference in being able to manipulate the lever without giving up my grip.

Does anyone know the weight of these?

Sig says 7.1 lbs.

Just got mine today.  Did an interesting test.  The lower will swap with the lower from my 556R.  There was a bit of resistance getting the 556R lower on the 556xi upper, but not enough to stop it.  Both seemed to cycle with each others lower.  Won't be firing it off to test it out unless Sig says it's okay. But was fun to test out.
Original rifles


Swapped lowers


The lowers


The Uppers

Nice, I'd really like to know how the xi 7.62 setup balances vs 556R.  The xi isn't a looker but it looks like it might balance better.

Well comparing the 556xi in 556 it definitely is a lot less muzzleheavy.

Yep, I thought so re: 5.56 but thanks for confirming.  Even though the 7.62 kit is probably slightly heavier, I bet the balance is slightly further back vs the 556R.

I don't mind it on the 556R (slightly front heavier than an AK) but it could be improved.

I assume the 556 grip will fit the Xi..........I kinda like the older grip

Hope these help. Let me know if you need different pics.

Inside


Bottom


Piston


Top

Thank you for that info! I thought the "previous" 556 weighed in around 8.5 lbs. Where/how did they shave so much weight off??

No problem.  According to Sig's site the 556 Rs and Patrols were already pretty close to the xi, but the Classics and DMR were heavier:

Sig 556R - 7.0 lbs

Sig 556 Patrol Rifle - 7.5 lbs

Sig 556 SWAT Patrol Rifle - 7.5 lbs

Sig 556 Classic - 8.2 lbs

Sig 556 Classic SWAT - 8.2 lbs

Sig 556 DMR - 9.5 lbs

If they work in both, couldn't you potentially end up with a non-serialized lower and non-serialized upper?  In theory?

Those are the pics I needed to see... it appears they redesigned the locking lugs into more of a half moon lug with a detent notch. That might not be compatible with the 55X classic gas block...



Any chance you could try to fit the XI gas valve into your 556R's gas block to see if it will fit?

Eric, I thought the uppers on all Sigs were serialized. When I was thinking of SBRing an older version of the 556, I was told by many stores it was the upper that would need to be sent off.

The upper has been the firearm on the 55X series since the day it was developed.

Yes, the upper is the "firearm" part of all Sig 55X rifles

Not going to work.  Here's pictures.
556xi top, 556r bottom

556xi left, 556r right.

Any chance you could shoot for accuracy at 100? If possible could you make sure the zero doesn't walk as the barrel heats? This was my chief complaint with the 556 I owned and if they fixed it then I need this. Thanks for posting so far. Looks great.

Well that pretty definitively puts a pin in that.

Thanks guys.

Damn. I figured it would be this way, but hoped it wouldn't.

 

I will try. Sadly the only outdoor range near me is 45 mins away and I usually don't have muxh time to go out there. I do plan on making a trip soon though!

Yep back to hoping someone comes out with a 3 position gas block for my 556.

Compared to my Colt AR, I find the 556xi to be stiffer and have less finesse as far as shooting 5.56x45.  That may be all Sig rifles.  I dont know first Sig I have ever owned.

How much did you guys pay for your xi's? I haven't found one in person yet.

$1,189 with free shipping and no credit card charge off Gunbroker.

1199 plus tax 1271 after tax,  (my serial number is less than 100, btw.  I never owned anything that was the first 100 made)

I paid MSRP like an idiot from Palmetto State ($1450 w free shipping)

But, I wanted one since I heard about them and jumped at the first one I saw.

$1010 but with shipping and FFL it was $1086.

ETA: Sorry, didn't read...mine's a 556R...

Do you mean more felt recoil, less ergonomic?

Not mocking, I'm interested in the xi.  Just trying to understand what you're describing.

Is your 556R a swat model? I can never find them. And online they seem to be overpriced. Cheapest regular 556R I've seen is $1250. I'm afraid once I find an xi in person I'll snatch it up. Guess it works out I never saw a swat model because I would have been upset that I bought one right before the xi announcement.

No just the poly hand guards.   It's already front heavy  (only slightly) so I wasn't interested in the extra imbalance.  At 7 lbs (no mag no optic) it's a good handling rifle.  

Would probably consider it if some variation of a super light rail like BCM KMR came out for it though.

$1345 for mine. - AZ

That's lower than what I thought it would be. I think the MSRP was $1450'ish range. But figured it would have been marked a little higher like any of the newer tacticool rifles like the Scar, Acr, and Tavor were when they hot the market. Granted the xi hasn't been in a Call of Duty or Battlefield game to have all the kids, airsofters, and neck beards to drool over, lol.