“The uppers and lowers are freely interchangeable, as are many major parts.
An AR-15 derivative is what I believe they call it.
I love mine.”
I handled one a few months ago and I like it. I think the grip design Sig came out with for that has the best ergonomics out there, at least for my hand. What I didn’t like was the trigger pull. Since you have one, perhaps you’d know, is the trigger interchangable with the dozens of aftermarket AR triggers?