Hello board ,
I am getting ready to order a complete post-ban Bushmaster M4a3 upper. Hope the waits not as long as I've heard. I've read on here about M4 cut feed ramps. What are these and would the upper I order from BM have them already or is it an aftermarket job. Just wondering so I can try to do it right the first time(if It would be best to have them that is).
  I have learned alot from this board That I know I could not have learned at any other site or place or book. Experience and know-how is the key and in here there is a ton of it. Another thing is you get information from all over the place, Different regions have different Ideas.
                  Thanks for all the help
                              silas

Do a search, there is a pic floating around. The cuts are Colt Patent, so you will find them on only new Colt M4 uppers. People are starting to dremel their own though.

Sorry, not a "Colt Patent". Extended feed ramps are available from Armalite, DPMS, and Diemaco. Bushmaster can, and has, added them on customer request. But, considering Bushmaster's current business situation, I would think they're far too busy for custom work. (IMO)

  Thanks for the responses and the pictures. It took me a second to spot the differences.
   Can you tell me if there necessary or not. Is it that big a difference between having them and not having them?

silas

If you're going to be shooting alot of full auto out of a carbine-length barrel then maybe you'd reap the benefits of the extended feedramps.  Otherwise I doubt you'd never know the difference.

The only possible reason to need them, is if the springs in your mags start to get weak or the mag gets dirty enough to slow the rise of the follower.  The only time I have ever had problems with the bullets hanging up on the receiver below the feedramps, was when I was shooting under-powered PMC out of carbine, with mags that had new followers just put in and were still a little rough causing the follower rise slower.  If I had changed my ammo or had smoothed down the edges on the mag follower, I wouldn't of had this problem.  So to sum it up, do you need them, no.