Posted this on the other board and didn't get much response so I'm trying it here:

I purchased an BM M4 upper a couple years ago and its been faithful to me.  Relatively accurate and reliable.  I'm a newbie to M4 style rifles and the question at hand is in regards to feed ramps?
I've heard of 'polished' or 'throated' (?) feedramps or something along those lines.  Can someone line me up and this term and explain to me:  1) should the M4 upper have them, 2) should they be 'polished', 3) who can do it?, 4) 'throated'? (terminology?) and what performance enhancement, if any, besides reliable feeding will it offer or supposed to offer.  I'm sure I don't have my terms correct here and would like some input from those in the know.

there was a thread in the AR section a while back about this, about feedramps and how you shouldn't try to throat them, iirc.  let me see if i cant find it for ya

ah here it is, this may help
linky

Colt has their own proprietary "M4 feed ramp" that you won't find on other mfr's M4's

Not sure if you tried the AR Discussions forum, they would have answers for you.
My experience has been that ramps need to be sufficiently clean, but not neccesarily polished.
I havent dont anything special to the feed ramps on my M4 style upper and it eats whatever I feed it. The difference I have seen between the 'M4' style ramp is that the ramp is cut into the bolt reciever flanges, where I have seen other uppers where the ramps cut starts a bit higher on the reciever face. Both have worked fine for me, so frankly, I think that as long as you are working with a quality upper, slap in on a lower and go shoot it.

If it present problems, revisit the issue...if it shoots without feed problems, I say leave it the way it is.

thanks for the replies


after checking the link its obvious that I don't have what is widely known as M4 feed ramps
thank for the info