Hi Muir
I got my first "Black Rifle" last year in the form of a HK MR 223, or as they are marketed in the US, a HK MR 556. I am very pleased with it, finally! When it arrived, I played around with it, field stripping it etc. Unfortunately, I did not assemble the bolt carrier carrectly and omitted to install the pin which holds the firing pin. Upon recharging the gun and dry firing, the spring for the firing pin was destroyed. I contacted my dealer in ZH and am still waiting, 16 months later for the German exporter to send replacement springs. Fortunately for me, I have a friend in the US, who sent me some replacement springs, after I bought some from HK Parts. Net!
I then decided to purchase an M4 but my dealer put me off the Norinco clones. He then produced a custom built M4 which has a Rock River Lower and a CMMG Upper; I cant remember if the barrel is 7 or 9 inches, but it is very short. It shoots brilliantly and has a 1:7 twist. I paid a small fortune for it, about 3 times the price of the Norinco, but I am very happy with it. I found out subsequently what it would have cost in the US to build...................sickened!
I have an HK MR308 on order, which is the HK's version of the AR10......if it shoots like the MR 223, I will be very happy indeed. I doubt I will get any more "Black Rifles" as I have covered every base as I see it. Also, my wife hates them as she thinks they look too aggressive or "war machines" as she calls them. The irony is, that she got me started in military syle weapons when she bought me a Sig 550 as a wedding present.....and a Sig P210.
All the best