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Posted: 5/23/2008 9:40:13 PM EDT
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Can someone please help me understand the over all premise of the barrel extension. Obviously I am new to AR building but I have tried to absorb as much as possible from this site. I have read the tutorials and am still unclear on barrel extensions. I believe I understand what the barrel extension does (sets headspace), but I am unclear if this is something you must purchase in addition to your barrel? I was under the impression that most barrels come with an extension. Is this not the case? I am also curious how to determine if barrels have have ramps to match up with uppers having M4 feed ramp cuts? To take this farther is it a must to purchase a upper with these cuts? Thanks, FrogFan |
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Usually when you buy a barrel, it already comes with the barrel extension on it and the gas hole already drilled. The barrel extension serves a good deal of importance. Before the barrel is even installed into an upper, the gas hole is drilled and centered off the index pin in the top of the barrel extension. Once the barrel has been installed into an upper, you check to make sure that the feed ramps match up from the upper to the barrel extension. This makes for smoother loading of the rounds. Now that all of that is ok, the lugs in the barrel extension work with the lugs on the bolt itself to ensure that the round stays in the chamber until the proper time for it to come out. The bolt lugs fit in between the barrel extension lugs and the bolt rotates so the lugs line up together to lock it into place. Older barrels only had ramps on the barrel extension and not the upper, now both the upper and barrel extension have them to some extent. If bought separately, they may not be a perfect match, but they will be there non the less. If bought as a complete upper half, they should be there and blended together to look like one continuous ramp. Hope this helped a little, |
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