Ok, i know this is probably a stupid question......What are M4 Feed Ramps and what are they for.  

Read this

Danny

OK, so if I understand correctly the upper has to match the barrel depending if it has the M4 or the standard.

Quoted: OK, so if I understand correctly the upper has to match the barrel depending if it has the M4 or the standard.

Yes.

Quoted: Read this Danny

Quoted: Ok, i know this is probably a stupid question......What are M4 Feed Ramps and what are they for.

I got one of the AR15.com group buy midlength barrels made in a special run by CMMG and ordered the M4 feed ramp option.  I had the barrel mated up to a LMT upper which is compatible with the M4 ramps (it has little ramps on it).  

Unfortunately it appears that the ramps on my barrel weren't cut deep enough such that when I try to run the tip of pencil along my ramps it hangs up on the shelf created by the mismatched ramp cuts.  This gives me concern that a cartridge could hang up as well and makes me wish I would not have ordered the M4 ramps at all.  I have not heard other's complain of this though.  

My plan is to see if someone can cut the ramps on my barrel deeper to mate smoothly with the ramps on my upper before I have this barrel assembled into a complete gun.  

Bushmaster did this to my upper 20 hbar 3 yrs ago

Can someone explain to me how this positivly effects reliability?

Thanks :)

Quoted: Can someone explain to me how this positivly effects reliability? Thanks :)

The M4 feed ramps essentially extend the ramps into the into receiver providing more ramp.  What I've heard here is that the potential problem is with full auto fire, so that you and I don't really need M4 ramps on our semi auto onlys.  It's just cool to say you have them.  It's mil spec for M4s and some want to be as close to that as possible.  Even if it's just for the cool factor.  

I'm not knocking them.  I got them myself.  But based on what I've heard here, they'll make no difference for me on my semi autos and I don't need them.  

Quoted: Can someone explain to me how this positivly effects reliability? Thanks :)

It takes weight off of the upper receiver allowing better harmonization between the barrel and the sling!

Quoted: Quoted: My plan is to see if someone can cut the ramps on my barrel deeper to mate smoothly with the ramps on my upper before I have this barrel assembled into a complete gun.   where in WA are you?

Eastern (Tri-Cities).  What do you have in mind?  I liked your old avatar better.  

My Colt Commando upper has the feed cuts.  
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Quoted: I was thinking I could clean up those ramps if you were close, I'm in Tacoma.

So it sounds like it's fixable then? Without too much trouble?   That would be good to know.  
I think I'll have ADCO (or similar) do it someday when/if I get enough $$$ and motivation to finish this gun.  I want the barrel profiled down anyway and probably a front rail put on.  Thanks for the help.  Your new avatar disturbs me.  

Well, back to the topic...

My 2 cents worth: making feeedramps out of aluminum is a less-than-satisfactory workaround - the alloy is softer than the steel barrel extension extension, and if/when the hard coat anodizing wears through, you could conceivably get reduced reliability due to deformation of the underlying alloy. This is somewhat of a concern with a factory M4 upper, but is a much bigger risk if your upper has been modified via the "Dremel method". Of course, I have no data to suggest that this is actually an issue with factory Colt uppers - army armorers from Iraq may be able to share an insight on how well the alloy feedramps are actually holding up.

For those who think M4 ramps are superior because everything Colt produce is golden, ask yourself why on earth Colt put the carbine gas port in the worse possible location - answer is that they couldn't find their asses with both hands. What has Colt's design team produced with any merit at all since 1911 ?

None of my rifles have M4 feedramps, and they have all been 100% reliable. If your rifle is not reliable with your choice of ammo and mags, then they may add value. Me - I prefer the rifle feedramps that Mr Stoner designed.