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View Full Version : Barrel Compatability, Extended Feed Lips


nrakid88
09-05-2008, 10:17 AM
Well, I have a CMMG upper with a 16 inch barrel, extended and polished feed lips. My question is that when I buy a 20 inch barrel, will it need feed lips at a different angle than spec ones so that the feed lips in the receiver match those on the barrel, or will any barrel work?

aplinker
09-05-2008, 12:59 PM
You'll need an M4-style ramps on the 20" barrel extension if you're going to install it in the M4 ramped upper.

nrakid88
09-20-2008, 2:11 AM
If anyone is wondering, I e-mailed cmmg and they said that the barrel is mated to the receiver for LIFE. and if i want a new 20 inch barrel, its feed ramps must be mated for LIFE with my old receiver, sounds like a crapppy situation, huh?

eaglemike
09-20-2008, 8:54 AM
If anyone is wondering, I e-mailed cmmg and they said that the barrel is mated to the receiver for LIFE. and if i want a new 20 inch barrel, its feed ramps must be mated for LIFE with my old receiver, sounds like a crapppy situation, huh?

I'm pretty sure there's an oops in there somewhere. You might not be using the same terminology on all sides of the conversation. The receiver doesn't have the feed lip, the barrel extension does. The barrel extension is usually mated to the barrel for life. The barrel assembly (including the extension) can be changed from receiver to receiver, or barrel assemblies can be changed in the original receiver. The barrel extension is the part that actually mounts to the receiver.
all the best,
Mike

aplinker
09-20-2008, 12:56 PM
I'm pretty sure there's an oops in there somewhere. You might not be using the same terminology on all sides of the conversation. The receiver doesn't have the feed lip, the barrel extension does. The barrel extension is usually mated to the barrel for life. The barrel assembly (including the extension) can be changed from receiver to receiver, or barrel assemblies can be changed in the original receiver. The barrel extension is the part that actually mounts to the receiver.
all the best,
Mike

M4 feed lips go all the way into the upper receiver - and the receiver has the lips, as well.

Randall has a nice pic showing some mis-matched and matched types.

eaglemike
09-20-2008, 7:38 PM
M4 feed lips go all the way into the upper receiver - and the receiver has the lips, as well.

Randall has a nice pic showing some mis-matched and matched types.
They aren't considered as matched parts, I'm pretty sure. I did go and check my upper (WOA, RRA) assemblies before I typed. IIRC, the M4 stuff stuff is considered necessary for full auto, but not for the usual semi-auto stuff.

shark92651
09-20-2008, 10:44 PM
I'm sure Randall has some better pictures but here is one I sent to someone when I was trying to explain it to them. I'm pretty sure the feed ramps (not lips, feed lips are on a magazine) are not "mated for life" with the receiver. I think he meant the barrel extension is mated for life to the barrel, but the barrel (along with extension) can easily be removed and a new one placed in the upper receiver and mate up to the existing feed ramps. As long as the barrel extension has the M4 ramps you are good to go. Having feed ramps in the receiver but not in the barrel extension is bad - could create a little gap in there where the tip of the round can jam up.

http://farm4.static.flickr.com/3290/2874910658_cf5932be98_o.jpg

ar15barrels
09-21-2008, 12:20 AM
Here's my picture:

http://ar15barrels.com/tech/feedramps2.jpg

Now, if you take a barrel and install it in a receiver and THEN take a dremel and blend the ramps together further, it's true that the barrel and receiver should live together forever.
If you swap those parts, you would need to re-blend the new reciever or barrel to get the parts to match again.
Ideally, M4 feedramps and M4 extensions will match up properly, but it's not always the case.
That's why people blend them better with a dremel.