First impressions:
The shotgun is well put together, with tight seams on the plastic components and good fit and finish with the forend rail lining up perfectly with the upper receiver.  The stock sights definitely leave something to be desired, but are easy enough to replace.  The shotgun is very light, more on that later.  The chokes included with the shotgun were Full, Modified and Cylinder.  The trigger is very crisp, no creep, very short take-up and low weight.  The ergos will feel familiar to anyone used to the AR-15.

So here is my experience so far with the BR-99:

This was the shotgun in the configuration I tested it in:

And the varied ammo I brought out to test the gun:



As you can see, the only thing I did to the shotgun prior to testing was change the sights to a set of Troy fixed I had on hand and disassembled/cleaned/lubed/reassembled prior to shooting.  I followed the break-in procedure as outlined, by running 50 high brass 00-buck shells through the shotgun.  The shotgun cycled the high brass shells 100% without any issues, and patterned well at 25 yards:

You can see where the wads chased the buck shot downrange:



Next I fired a magazine of slugs off hand at 25 yards to see what the point of impact looked like:

And after I figured out the hold over (the irons are a bit high over bore) I fired another mag of slugs:


I followed this with more slugs, buck and bird shot, with the Winchester Dove loads (pictured above) being the lowest brass shells fired today.  All of them cycled fine, and there were only a few hang-ups all day.  I later determined the shells which did not fully cycle came from a box all of which looked like this:

As you can see the shells are not round at all, and stuck partially in the chamber after firing.



TL;DR, Conclusions, Whatever:
1. The shotgun is well built and very solid for being primarily composed of plastic.

2. The shotgun is very light, resulting in high recoil compared to other semi-autos.

3. The trigger is amazing, I can't stress this enough as it is the nicest shotgun trigger I have ever felt.

4. Straight drop/load mags are a godsend compared to other mag-fed shotguns

5. Mags are a pain to load as the brass from one shell catches on the rim of the next shell, necessitating pushing the shells in the mag down prior to loading the next shell.

6. The shotgun patterned predictably and was reasonably accurate with rifled slugs offhand (no bench testing as I didn't have a bench )

7. The shotgun ate everything I threw at it, and ran fine, high brass and low brass shells didn't make a difference.

8. Also on hand today for comparison was a Saiga S-12, which failed to cycle the low recoil slugs at all, and would not cycle the Dove loads either.

9. It's fun shooting stuff, even when it is hot as hell out.

Finally, S-12 vs BR-99 vs Winchester SX2:

Saiga S-12:
Heaviest by far
Lower recoil than the BR-99, but far more than the SX2 (also has an auto gas plug, so the recoil stock would have been worse than the BR-99)
Won't cycle the same variety of ammo as the BR-99
Would not cycle the low recoil slugs at all
Rock-in mags suck

SX2:
Middle weight of the bunch
Softest recoiling
Not mag fed (big negative)
Chokes occasionally on low brass bird shot and frequently on the low recoil slugs

BR-99:
Lightest of the three (big plus)
Highest recoil (not a problem as long as you aren't a pussy, probably has to do with the low weight)
Straight drop/load mags for the win
Ate everything without complaint, even the oblong, low recoil/pressure craptacular slugs (most reliable with a variety of ammo)

Thanks for the post, OP.

I would like to mention that through out the day, the wind was kicking up a lot of fine dust.  When I disassembled the shotgun to clean it last night (after posting the review) I found the action had a rather inordinate amount of grit and carbon adhered to every moving surface and the gun still ran fine.  That's saying something about its reliability.

Also I would like to make an ongoing list of things I would like to see made available for this shotgun:
1. Lower receiver which takes AR stocks and grips.  Preferably, either with a built in BAD lever type bolt hold open or clearance to accept a BAD lever
2. Drum magazines in 10rnd or greater flavor, preferably with a clear back panel for the sake of having a quick visual reference to how much ammo is left in the gun.
3. Lower rail for the foregrip.  I can't stress this enough as a shotgun without a flashlight is like a car without headlights.
4. A provision for a left side charging handle would be nice, but isn't necessary.

I will add to this as I come up with stuff

Any idea if it takes MKA 1919 5 rounders? I don't like the look or price of a 10 rounder, I would buy one 10 rounder and keep 5 rounders on my battle belt, so I would like at least 3 of those.

That is exactly what it takes, the owners manual even refers to it as a MKA 1919 so I'm guessing it is more of a revision than a whole new gun.

ETA: it comes with 2 of the 5rnd mags.

5 round mags available here.

Is there a difference between the 3" and the 2.75" mags?

The mags are all 3" but they work with 2.75" shells as well.  I had no feeding problems regardless of shell length.

I love my MKA1919 but would rather have started with the BR-99 as I like that hand guard and top rail much more.  I still would have chopped off the stock and grip and gone with the MagPuls as I have done (with Enidine Stock Buffer) but at least I would have the nice top rail and hand guard without going after market.

MadDog

What muzzle device is that?  I'm interested in one...

I also wanted to add that it is easy to insert a full mag on a loaded chamber and it cycles fine when starting with one in the chamber and the mag to capacity (much unlike the S-12).

Trying to find out the Length of Pull and also the Stock length, and will a Tooth & Nail forend fit in place of the original ?

My understanding is that the T&N forend will fit.

Short LOPs exacerbate perceived recoil.  Probably a contributing factor to what the OP reported.  It a neat looking gun and I'd like to see one in the flesh.