Jeff put it more succinctly that I could.
Personally, having trained with it, I am very fond of the MP5 in 40 S&W (haven't tried the 10mm version) and it holds a special place in my heart. I am also familar with the G3 series of rifles and have lots of experience with the civilian versions in 7.62 and 5.56 mm Nato. Use to shoot a HK91 rifle virtually every other weekend when I was in college (they cost only $385 new back in 1978). While the HK53 and the HK family of weapons certainly has its merits and a lot going for them, Jeff is right on the money when he talks about
advantages of the M4.
As part of the M16 family of weapons and no extra training being required. Another major advantage mentioned by Jeff is the commonality of parts (in our armed forces). Military armorers won't have to stock up on so many extra types of parts, have another set of tools (did you realize that there's a special dent removing tool for the HK receiver which probably costs about as much as a mortgage payment?) to service a 2nd type of gun, and require additional training? Think of it, two soliders, one a truck driver with an M4 and another an infantryman with an M16. They can trade rifles without having to trade magazines. How much simplier can it get?
Is the Stoner system superior to the delayed blowback of H&K? I won't get into that here and I think Edmund Rowe started an interesting thread elsewhere in The Firing Line which you may find amusing.
