It is "reinforced" because they replaced a few internal parts.
Yes, it does fit.
And on to the real review:
This is a great, strong gearbox. Out of the box, our A&K M249 was shooting ~400 FPS @ 10 BPS with the stock 8.4v battery. When we dropped in a 9.6v battery, it was going at more around 17 BPS. From 50 feet away, I was able to massacre a beer bottle. Also, at ~100 feet, rounds from the SAW would stick in or go through the sides of Pringles cans.
That's REALLY good, if you were wondering.
Another GREAT part of this gun is; quick spring swapping! Merely push the spring guide in and pull out, drop in a new spring, click the spring guide back in, and you're in business! I wanted to try dropping in an M100 equivalent spring, but the owner had to leave. I'm pretty sure that ti would have gotten Li-PO-esque ratings with an M100 in it.
Rating: [5 of 5 Stars!]