I was just looking for a second opinion and to see if the information I have is correct or if I need to have something done to my weapon. The manufacturer of my MP5SD semi-auto (I believe it was an HK94 because it does have correct import markings and is HK origional), he says Quote: "I used win white box to test fire your gun several rounds no problems." Right now, the weapon in question is at my local dealer waiting on the tax stamps to come back. I've test fired it but I've been having a little trouble with it cycling different ammo. I know that these weapons can be "picky" about what ammo they like so I bought a variety to test it with. I've tried a few different weights and manufacturers including Remington UMC 115gr value packs (Yes, the yellow box. I've already heard about the value packs and their deficiency with "Subguns" and just wanted to see if mine was any different... obviously not). I've tried regular Remington 124gr (green white box), American Eagle 124gr, Blazer 124gr, but it only cycles properly on the Winchester NATO 124gr. I've been told by a couple trusted friends and shooters that it should work with the 115gr stuff. I've also been told that "European guns prefer the higher pressure NATO stuff". This isn't the "F" model mind you and I don't think its using any of the "F" parts, its the plain-Jane MP5SD with Action3 roller and semi auto group (there is no cut out in it for the sear trip). This was a fresh build so I'm wondering if it just hasn't been fired enough to "break it in"? Or if I'm just not using the right ammo? Or if the malfunctions may have something to do with the guns set up thus requiring some work to it? Is there something I'd need to check like bolt gap or head spacing? (This should have been done right from the manufacturer. It has the 115 degree locking piece, would the 120 degree piece make a difference? Any information on trouble shooting this would be very helpful.