M4 Feedramps

[arizonaranchman]

Excellent summary and analysis! Thanks for sharing...

[AR15barrels]

I can see from this proceedure that there would be no way to assure that the gas port hole is drilled in the middle of a valley in the lands & groves of the barrel. It is drilled according to the ramps and at the distance where it needs to be and how it lines up with the rifling is inconsequential.

If it's important to someone that the gas port ends up in the middle of a groove, then the barrel would be threaded for a barrel extension, but not chambered.
Then the barrel extension is torqued on and the gas port location is checked with a borescope.
A determination is made as to how much more rotation is required to center in a land.
Then the shoulder of the barrel is cut, the length of the extension threads cut and finally the barrel is chambered.
When the extension is re-installed, there will be a groove centered where the gas port is to be drilled.
This type of work is only done on a custom basis.
It's far too much work to do in a mass production environment.

[RyanB]

Are M4 cuts necessary on an SPR? Ostensibly they have them to protect the bullet.

[MarkG]

Feed ramps only exist in the barrel extension. The other “feed ramps” as they are often referred to in the upper receiver are more accurately defined as clearance cuts. Their purpose is not to guide the ammunition into the chamber but to prevent it from hitting a 90 degree corner and glancing off as the scalloping of the carbine barrel extension causes it to end short of the common edge with the upper receiver. All of the photos used to illustrate what the different ramps look like, rifle (45 deg) vs. carbine (52 deg), typically provide a from the rear chamber view. A side cutaway would clearly illustrate the necessity of the clearance cuts and why they increase reliability in the M4 carbine and its commercial counterparts.

[AR15barrels]

Feed ramps only exist in the barrel extension. The other “feed ramps” as they are often referred to in the upper receiver are more accurately defined as clearance cuts. Their purpose is not to guide the ammunition into the chamber but to prevent it from hitting a 90 degree corner

However in doing so, the "clearance cuts" do indeed help to guide ammunition into the chamber. If you examine a few M4 cut and non M4 cut uppers with high round counts, you will no doubt see the copper deposited both on the 90 degree corner and in the clearance cuts.
This copper deposit is obvious evidence of the usefulness of the M4 cuts.

[4thPointOfContact]

The problem with this is "M4 ramps" existed well before there was such a thing as an M4 carbine.

Now you've got me curious; just when did the "M4 ramps" make their appearance?
In a production model, or in a prototype?

[SVT-ROY]

Very good info! I have been curious about this and didn't know what to look for. My m4gery has both the m4 feed ramps! Cool I guess.

[scottryan]

Now you've got me curious; just when did the "M4 ramps" make their appearance?
In a production model, or in a prototype?

Colt started using extended feedramps around 1990 to 1991 on its carbines.

[Dangerousdan]

This is valurable information, I'm looking forward to more of the same.
Thanks.

[mkmckinley]

can i use M4 barrel on A1 reciver? please explain it in detail.

It seems to me it's been explained in minute detail earlier in the thread. Did you bother to read it?