I recently acquired an MSAR STG-556. It is chambered in 5.56 NATO 1/8 twist with a 16" barrel. The one I got was a flat top with a 1913 Picatinny rail. It came with a BSA RD30 red dot sight that had a flush mounting system. This was the only means of aiming the rifle, and for obvious reasons needed to be changed.
When using the RD30, a proper cheek weld was easily accomplished and the dot could clearly be seen at the highest setting of 11. I immediately removed the RD30 and made my way to the local gun store. Upon arriving I spotted a MeproLight M21 red dot reflex sight with the x reticle . I purchased it and went home really excited to mount it to my new rifle.
The M21 came with a really solid quick detach mount, throw arm style, so I figured it would be plug and play. Boy, was I wrong. First, I found the proper place on the rail for the M21 and then I mounted it using the throw arms. It was quick and simple.
I raised the rifle to a firing position and got a proper cheek weld. All I saw was the base and a little bit of glass. After moving the M21 up and down the rail I got the same results each time. Apparently the quick detach mount was raising the sight too high to achieve a proper cheek weld. If I raised my head just a bit, the sight picture was right where it was supposed to be.
So now I have two options. First option is to raise my head a little and not be able to achieve a proper cheek weld, but I would have a correct sight picture. Second option was to remove the factory quick detach mount and find a lower profile mount. The mount itself is only inch high, so I don't think that solution was going to work. Also, after some research, I found out the mounts are calibrated to the optic at the factory. In essence, neither option was going to be acceptable for me.
I then found a company called Promoted Pawn. They specialize in aftermarket parts for the STG-556 and FN P90. They make an optics rail specifically for this inherent problem with the flat top STG-556s. I ordered the rail and a set of their QD sling swivels. The rail was $150 and the set of two QD sling swivels was $30. So $180 with no shipping charge. The items took about a week and a half to arrive at my house.
The rail is machined from a single piece of billet aluminum and features 23 Picatinny slots versus 19 slots on the stock rail. It is a little longer and a little shorter than the stock rail. The QD sling swivels are entirely made from stainless steel and have a more solid build than the stock ones. Both parts feature a lifetime warranty.
Installation was fairly simple and the Promoted Pawn rail came with three attachment screws. So really all I did was remove the three stock screws and rail and replace it with the aftermarket rail and screws. Obviously the new QD sling swivels just popped right in.
I mounted the M21 and found I had a correct sight picture while using a proper cheek weld. I also like how the rail is about 2 inches longer for giving you additional sight radius when using irons. Thankfully this was an easy fix, but it cost some money for the correction.
I have recently traded the M21 and I don't have irons for her yet, so I have yet to shoot it. Currently I have no sighting system for it, but when I do I'll update how the rail performs under fire. My initial impressions of the rail and QD sling swivels are that they are both top notch quality products. Hopefully that doesn't change when put under stress while firing the weapon.
Pros: Robust construction, rail is in 1913 spec, retains the classic AUG look with the space between the receiver and the bottom of the rail towards the ejection port.
Cons: The front of the rail isn't wide enough to match the front of the upper receiver, the color is ever so slightly off (minor), the rail markings are not color filled white like the stock rail (minor).
I hope this helps anyone else that has an STG-556. There isn't a lot of info on them, or any bull pups for that matter. I will update as I continue to build her.
Stock optics rail
Closeup of stock optics rail
Stock optics rail height
Promoted Pawn QD sling swivel on the left, stock on the right
Stock parts on top, Promoted Pawn parts on bottom
Stock rail on top, Promoted Pawn rail on bottom
Promoted Pawn optics rail installed
Promoted Pawn optics rail height
Rifle with Promoted Pawn optics rail
Promoted Pawn optics rail is not wide enough to match the upper receiver