A while back there was a thread from Big Red and KevinB regarding some problems with the SG 552's in Iraq. Some bolt carriers had broken during use.
I have some experience with both the Swiss Arms CQB and SG 552. I own a CQB and I'm currently issued a SG 552. My experiences have been very positive. I have just over 3000 rds through my SG 552 (auto, burst and semi auto fire) and about 600 rds through my CQB. Both have been outstanding weapons. Our SG 552's in service have never experienced a malfunction of any kind. This includes minor things such as locking open on an empty mag. They have been perfect. They operate very smoothly and are easy to control in all modes of fire. The triggers are what sets them apart from most other weapons. Extremely accurate. We fire light, heavy and frangible ammo. They point very naturally and come on target easily. Some weapons are just easier to make hits with and the SG 552 is one of the best I've ever been issued in this respect.
At the Shot Show I spoke to one of the instructors from SIGARMS about the SG 552 (must consider the source as he works for the company that represents and sells Swiss Arms to US Law Enforcement.) He stated that in the tens thousands of rounds that he has fired through the SG 552 and 551 he has seen very few problems. He has changed two extractors and the recoil spring guide rods on the SG 552's use to break until they were replaced with the upgraded plastic ones. He also stated that the SG 552's used to get "beat-up" under heavy use. This was corrected a few years ago when the gas plug / regulator was changed in the SG 552. (I wonder if this was the problem that the SG 552's had in Iraq?) He also stated that the FBI and DEA extensively tested the SG 552 and 551. They are approved weapons for both agencies and are in their inventories. The Rock River Arms weapon is also approved and is half the cost so it is therefore the dominant weapon in use by those agencies (a smart decision from an administrative position.)
I have information that the UK SAS ran a trial regarding short barreled 5.56mm weapons for CQB use and the SG 552 beat out all competitors. (This is very interesting as we know that the Colt Canada SFW won an earlier trial and is the general issue weapon of this unit. It would seem that it would be natural to select the Colt Canada CQB as a partner to the SFW.) The OPP also ran a trial between the Colt Canada CQB and the SG 552. The Colt weapon won the trial, but when speaking directly with an Officer involved in testing it was not entirely due to better performance. (The "Gun Guys" / proficient shooters, involved in the test, perferred the Swiss Arms 552 and it proved to be more accurate.)
There are some negative points to the SG 552;
The gas system gets extremely dirty after extensive firing and is labor intensive to get clean. The up side is that the weapon will continue to function even when utterly, disgustingly dirty (the bolt stays clean though).
Stripping is more complicated than some other weapons. No small parts but never the less, more parts. (This was one of the OPP complaints with the SG 552.)
Mags have to be "rocked" into position. Empty mags usually have to be grasped and released with your thumb. (I see this as a positive aspect as when a mag is "rocked" in place it is secure. There's no such thing as not seating a mag. Either it's in or it's not.)
Cost. In most Countries the SG 552 is more money. In the US, the advertised Law Enforcement price of a Colt Commando is $795. What administrator is going to buy the SG 552 when you can purchase 2 RRA's or Colt's for the price of 1 Swiss Arms weapon.
Noise...noise...muzzle blast...flame...noise. All short barreled 5.56mm weapons experience this though.
I got a little long winded. Just some of my experiences with the weapon. I've been issued and used quite a few different weapons over the years and the SG 552 is the best I've ever had.
Rich
P.S. The night sights will hit in exactly the same point of impact as the iron sights if you use the dots. If you try and use the top of the post on the flip up night sight it doesn't work and will hit high. Impact will be where the dot is, not the top of the post.