Re: MRP Recce and SPR builds.....
Recce is basically a 16" bbl SPR. I read somewhere that some SF dudes wanted a smaller package, so they had the bbl shortened. I don't think there is an "official" version.
From a lot of builds I've seen, many just consider Recce to be a precision carbine. They tend to have optics that would allow for fast up close shooting. So, like a reddot in conjunction with a variable power scope. Others will run some 1-4x scope like an accupoint or the shortdot or an aimpoint with 3x mag in a flip mount. Also they tend to not have bulky stocks or fixed stocks.
I think the popularity is because this style carbine is tactical looking but well suited towards 3-gun. Sorta a do-all AR-15.
Funny thing is that I RARELY shoot my Recce style carbine. Also funny is that I am constantly changing it's configuration. In the end I either just shoot my 14.5"(pinned to 16") or my SPR.
What gets me, is why more people don't try and build SAM-R's. They're pretty neat too.
I've got to say something. Based on my estimates, that carbine recce that you built(sans optics) cost less than an ACR basic and I'm certain it's a WAY better setup than an ACR full. It does all the things an ACR is supposed to be able to do, and it is built on a proven system by two of the most reputable companies out there. It really is a perfect mating of an upper to lower. Probably the best out of the box combo I've ever seen. I've spent many many hours trying to piece together parts for perfect builds... and here they are. <sigh>
The only thing I'd do different is use Larue SPR-S mounts and put some podlocs on those bipods.