I don't want to start a flame war about whether or not M4 feed ramps are good/bad/ugly/indifferent/whatever.  I've been doing quite a bit of looking around on the internet, and have decided that when I finally get around to building my AR, I'd like them to be on there.  Now, the question is this:  Are M4 feed ramps standardized between the various makers of receivers and barrels?  I know you can get into trouble if you've got an upper that has them and a barrel extension that doesn't, because it'll make a lip for the bullet to ram into and jam up.  It seems like the same thing could happen if the feed ramps were cut more aggressively into the upper than the barrel, creating the same lip problem, so how does a guy avoid that?  Do the barrel and upper have to be from the same manufacturer?  Or will M4 feed ramps from one (reputable) manufacturer of barrels just match up with M4 feed ramps from all the other (reputable) makers of uppers?

After you assemble your barrel and upper you have to feel the ramp how smooth it is.  Push your finger in the groove toward the barrel and see how it feels.
If it steps up then you will need to smoothen it out with some sanding rolls then polish. If it steps down you could leave it.

I have an upper with feed ramps that were polished/blended to a previous barrel.  Its wearing a Colt M4 barrel now and the ramps dont line up, they have a small gap that easily catches with a scribe or small screwdriver blade.  The gun still runs like hot butter.

What brand were you going to go for your upper and lower?

I was wondering about this very issue. Seems like some say the ramps are necessary while others say its just a feature used by retailers as a selling point. I've heard that without M4 ramps you will likely suffer a jam once in a thousand rounds. I suspect improperly cut/matched ones will probably cause more issues than that. Are they really necessary? I know some want their guns to be 110% failure proof because their rifles will be used for SD or in tight situations but if there's very little chance that your rifle frame will dismount, jog a 100 yards to your bench and kill you before you clear the jam, is it really all that important? Sorry if this is a stupid question but I'm reading up on this stuff as much as I can and am still green.

If the choice is between M4 feed ramps or not, all other things being equal, why not get the m4 feed ramps. Most sellers now include the feed ramps anyway. That said, not having them is wouldn't be a deal breaker for me.

If the choice is between M4 feed ramps or not, all other things being equal, why not get the m4 feed ramps.

This

After you assemble your barrel and upper you have to feel the ramp how smooth it is.  Push your finger in the groove toward the barrel and see how it feels.
If it steps up then you will need to smoothen it out with some sanding rolls then polish. If it steps down you could leave it.

If your barrel is chrome-lined, you can't really do that, can you?  Doesn't the chrome coating extend to the barrel extension?  I don't know what upper and barrel I'll get yet, but I do want to put it together myself; so I'm hoping to get a barrel and upper that will go together correctly without having to take a Dremel after my brand-new rifle.  I guess I might just have to go to the various local gun shops and see what the grooves look like on various barrels. 

Whether or not to get them, I agree with 2A and Voodu; they're offered, they don't really raise the cost of the components, and they (may) increase the reliability of your rifle.  Even if that means it jams once every thousand rounds instead of twice, I figure it's worth a little extra homework to have them.

Quote from: SpeedTek on January 07, 2012, 01:05:08 AM

After you assemble your barrel and upper you have to feel the ramp how smooth it is.  Push your finger in the groove toward the barrel and see how it feels.
If it steps up then you will need to smoothen it out with some sanding rolls then polish. If it steps down you could leave it.

If your barrel is chrome-lined, you can't really do that, can you?  Doesn't the chrome coating extend to the barrel extension?  I don't know what upper and barrel I'll get yet, but I do want to put it together myself; so I'm hoping to get a barrel and upper that will go together correctly without having to take a Dremel after my brand-new rifle.  I guess I might just have to go to the various local gun shops and see what the grooves look like on various barrels. 

Whether or not to get them, I agree with 2A and Voodu; they're offered, they don't really raise the cost of the components, and they (may) increase the reliability of your rifle.  Even if that means it jams once every thousand rounds instead of twice, I figure it's worth a little extra homework to have them.

Only the chamber and bore are chrome lines, the barrel extension is regular ole chrome moly steel like the outside of your barrel.  Just make sure if you do this that you are removing the steel and not the aluminum of the receiver, as the aluminum will polish away a lot faster than the steel.

Ok, great.  I guess it sounds fixable even if the barrel extension and upper don't quite match up.  Thanks for the info, fellas! 

Shoot it before you fix it, you may find its irrelevant and attempting to fix it could actually induce problems.

Shoot it before you fix it, you may find its irrelevant and attempting to fix it could actually induce problems.

Very sound advice. Don't fix what "ain't" broke