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Posted: 1/31/2011 2:18:47 PM EDT
I'm kind of new to working on ARs so this may be simpler than I'm making it. I currently have an A1 upper receiver and want to change to either an A3 or A4 receiver. I'm going to keep the same barrel and everything. My question is, with the extended feed ramps, will the A4 work? I would like the bigger ramps, but I got to thinking that the ramps might not work. If the A4 doesn't work, then should an A3?
Link Posted: 1/31/2011 2:49:49 PM EDT
if your barrel extension does not have the m4 feed ramps it may cause problems if your new upper reciver has them. you will need to blend them smooth for propper function.

however i believe you can buy a3 and a4 recievers with or without the m4 feed ramps. if your barrel has the m4 ramps using either reciever would work
Link Posted: 1/31/2011 2:52:52 PM EDT
I can only assume you are concerned about compatibility with barrel extensions from one receiver to the next. Assuming your barrel has a standard barrel extension to match your existing A1 upper, if you were to switch to an A3/A4 upper with m4 feed ramps you would run into an issue. However I believe you may be able to find an A3 style 'flat-top' upper without m4 feed ramps, in which case you will be good to go. Here is the often quoted diagram for reference:

Link Posted: 1/31/2011 4:02:46 PM EDT
A4 uppers don't have extended feed ramps, M4 uppers do. I'm guessing since you have an A1 upper your barrel has rifle ramps, so just make sure you get an A4 upper instead of an M4.
Link Posted: 1/31/2011 5:52:26 PM EDT
Alright. thanks for the help guys. How hard would it be to switch the barrel extension? I got to looking at it and they seem like they would provide more reliable feeding. I may be way off base, though.
Link Posted: 1/31/2011 6:05:53 PM EDT
[Last Edit: 1/31/2011 6:25:50 PM EDT by hunterboy56]
Or do M4 ramps make that much difference?
Link Posted: 1/31/2011 8:07:46 PM EDT

Originally Posted By hunterboy56:
Or do M4 ramps make that much difference?

No, not really. And changing the extension might as well be impossible. However, dremeling M4 feedramps into your current extension is easy. Really no point in doing that though when you can get an upper that doesn't have the ramps.
Link Posted: 2/1/2011 3:21:55 AM EDT
Alright. Thanks again guys.
Link Posted: 2/2/2011 3:04:34 PM EDT
FYI the barrel extension is screwed onto the barrel, the headspace set, and then it is pinned to preserve it. Since the gas port gets cut to place it at the proper part of the rifling, there's already a nominal Up^ and the ramps are cut relative to that. It's a working assembly at that point.
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