Quickie ar-15 question

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jojo200517

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I'm not really a fan of the ar-15 but I have noticed something about them as I browse the internet and see various pictures. Some but not all of them have a bump (or rather a dip) in the barrel part way between the front sight post and the flash suppressor or whatever muzzle end device there is. What i'm talking about is the part where the outside of the barrel is smaller for a short distance before returning to the previous outer diameter as in this picture http://www.stingerdefense.com/media/catalog/product/cache/1/image/5e06319eda06f020e43594a9c230972d/a/r/ar15.jpg


The question is what is the purpose of this place where the barrel size changes on the outside? Why do you see it on some models but not others?
 
My understanding is that the profile was originally intended to aid in the mounting of a M203 40mm tube under the barrel. Also, these barrels are typically smaller diameter under the handguards. This cuts down on the weight as well.

Dang, beat out by mljdeckard by a matter of seconds. :)
 
Oh ok that makes sense, so it basically has nothing to do with the firing of the rifle itself.

If I would have had to guess before I would have thought it was the appropriate place to cut one for SBR to thread for new flash hider location without having to turn down in a lathe first. Guess my guess was way off.

Thanks everyone.
 
It's true..... unless you ask one of my old Platoon Sergeants. He swore up and down that it was put there so that it would be easier to bend the barrel should the weapon become inoperable, or you were forced to surrender.


Truth is the cut-down portion is just what the original barrel diameter was on the M16/M16A1.
 
It's true..... unless you ask one of my old Platoon Sergeants. He swore up and down that it was put there so that it would be easier to bend the barrel should the weapon become inoperable, or you were forced to surrender.
Click to expand...

Sounds like he had his head so far up his fourth point of contact it was up near his fifth point of contact. (Or 3rd, if he landed like I always did, feet, @$$, head.)
 
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