Well, I can give you some specific differences between the configuratuions. As far as use, etc, I cant really help there... This is all from memory and I admit up front I have no real knowledge of their use and what real parts may be used. This is all stuff I've just gathered from general interest. If people who know better see mistakes, please correct them. Thanks...

SPR - Special Purpose Rifle. Two "official" versions exist;
MK12 Mod 0 will use a 12" PRI FF tube with ARMS SPR rail. PRI gasblock/flip up front sight, ARMS #40 back up iron sight. 18" Douglass "SPR contoured" (midweight) barrel with a rifle length gas system. Ops Inc 2 port muzzle brake with collar and thread protector. ARMS #22 Med rings, first with Leupold LR/T 3.5-10 optic, later with Leupold MR/T 3-9 optic. Knights 2 stage trigger and initially a Versa Pod, later a Harris bipod. A2 (maybe even A1?) stocks. Real ones also used Ops Inc sound suppressors. Here's a pretty dang near perfect clone of a SPR MK12 Mod 0:


MK12 Mod 1 will use a 12" Knights FF RAS with a Knights low profile gas block and Knights rail mounted flip up front sight and Knights 600m rear sight. 18" Douglass "SPR contoured" (midweight) barrel with a rifle length gas system. Ops Inc 2 port muzzle brake with collar and thread protector. ARMS #22 High rings with Leupold MR/T 3-9 optic. A2 (maybe even A1) stocks. Knights 2 stage trigger with Harris bipod and Ops Inc sound suppressor. Here's a pretty dang near perfect clone of a SPR MK12 Mod 1:


DMR - Designated Marksmen Rifle
Uses a Daniel Defense 12" free float rail with a 20" heavy, fluted under the handguard barrel (I dont know whose barrel is used). Standard A2 stock, flash suppressor and A2 front sight. I think these were using two different scopes, a Trijicon ACOG of some sort (my guess is either the TA31-F or TA31-RCOA4) or a Leupold MR/T 3-9 in ARMS rings. I dont know if a BUIS was used but if it was, I would bet it was either a Knights 600m rear or a MaTech rear. Some two stage trigger was used, probably the Knights, but there could be others as well? This is a real SDM-R:


Recce - Recon Rifle (Recce is pronounced like Becky but with an "R")
I think they used 16" Lilja barrels with mid length gas systems. A 12" Knights FF RAS. I think the LMT SOPMOD stocks were used. I think there is a variety of scopes being used, NightForce 2.5-10, Trijicon ACOGs and maybe even the same Leupold MR/T 3-9. Who knows for sure though, could be even more variety? Dont know if there is a specific front or rear folding sights being used or not? Here's an example of what one might look like;


As for the board here on AR15.com, the terms get used pretty losely, and it doesnt really make a big difference. Right or wrong, SPR is now a pretty generic term for any 18", 20", or 24" accuraized AR15. right or wrong, DMR is generically used to describe an accurized flat top 20" AR15, usually with a fixed front sight and an ACOG. Right or wrong, Recce is generically used to describe any accurized and still capable at close range, 16" AR15, usually with a full length rail.

Wow, Lawman, nice guns!