I have been shopping for an M4 style AR for some time and I saw the Sig M400 on sale for a really good price so I picked it up, it came with a Magpul stock and forend. I of course wanted to add some things to it, I purchased the B.A.D. Lever, ASAP - Ambidextrous Sling Attachment Point and a MS3 sling.
First thing I did was go to put Sling attachment on, well with the Sig lower it doesn't fit as the Sig lower needs a flat plate instead of the Magpul with two bosses so I had to grind off the two bosses to make it fit, looks nice but sucks that I had to modify parts that were supposed to fit. Went to put on the B.A.D. lever the same thing didn't fit had to grind the lever so it would clear the mag release button and again on the radius to clear the boss surrounding the mag release button, then I had to touch the areas that I had modify. So I was rather disapointed in this from Magpul.
The pictures for the MS3 sling were backwards, I had to read the instructions to get it to work properly.
However the Mags work great!!!