AR Upper build question

[jvpark]

I am buildling my first AR upper (I have built lowers and want to learn how to complete a upper) and have read some uppers come with a built in m4 feed ramp and some barrels have the M4 feed ramp attached to the barrel?
Is it more popular to have a AR barrel with the M4 feed ramp extension attached or when I go to buy the barrel, I have to ask for one with a M4 feed ramp extension?
What is is the standard?
Thanks and hope someone can school me on the process...

[kcstott]

M4 feed ramp only are really necessary for burst or full auto fire. That said AR have M4 feed ramp because that's what was on the upper.

The feed ramps are part of the extension as well as cut into the upper. So if you want M4 feed ramps you need to specify that to the builder or read the spec if provided on the upper you are ordering.

[Insight.556]

^^THAT^^

The M4 feed
Ramps are located on the barrel extension, but also cut out on some uppers.

Both the upper, and barrel extension will need the feed ramps to mate properly. In many cases the feed ramps on the barrel extension may not fully align with the feedramp cutouts on your upper so it may be necessary to dremel it a tad ,and then polish both ramps (barrel ext. + upper) to get it nice and smooth. (Even a nice Daniel Defense 16" CHF barrel and a DD A4 upper I was recently assembling didn't mate up 100% smooth and needed to be dremeled and polished)
Here are some web examples:

[jvpark]

^^^
Thank you!