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Old November 30, 2007, 11:32 PM   #1
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Headspace in an AR-15

I recently bought all of the parts necessary to build a 16'" AR-15 (all the parts are brand new usgi spec). This will be my first attempt at assembling a firearm from components, as opposed to buying a rifle ready to go.

My concern involves the headspacing, I bought the barreled upper and bolt assembly separately to save some dough, so it hasn't been professionally headspaced. For all the talk of AR's almost being like legos, as a novice "gunsmith" is it reasonable to be able to install the bolt assembly in the upper receiver without major issues? Ive been looking at buying a set of headspace guages and using those.

Is this something that should be strictly left to the professionals?

-The last thing I want is an unsafe situation
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Old November 30, 2007, 11:44 PM   #2
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I just did the same thing (bought BCG and upper separately). Although I found web pages that said, basically, "don't worry about it," I got a GO guage and a NO GO guage from Midway for $17/ea. and checked the headspace. It was fine. You need to remember to remove the extractor from the bolt when you check it.

I might not have purchased the guages if I didn't already have another build in mind where I'll use them, but now I've got them and any future bolt/BCG replacements can be checked.

At arfcom there's a helpful thread about headspace.
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Old December 1, 2007, 10:48 AM   #3
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I've built many uppers over the years, starting in the mid 80's when my first AR (Sendra) came to me as a kit. I've never once checked headspace on any of them and they've all worked fine. If you decide against buying the guage, chances are you'll be fine. But if it makes you feel better, buy one.
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Old December 1, 2007, 11:54 AM   #4
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Don't worry about it, the headspace on an ar15 is set by the barrel extension, which is the part the bolt engages with it's lugs. This is different than a typical bolt rifle, which the bolt engages lugs in the reciever and the barrel is screwed to that. The barrel extension on an ar15 is set at the factory on the barrel at the correct distance and headspace so you can install it on an upper and not worry about it. Save your money for ammo, mags or accessories, don't waste it on guages.
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Old December 1, 2007, 12:50 PM   #5
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The first time I bought an AR upper for my Colt HBar it was at a gun show, these were uppers that were in boxes without complete bolt and carrier. He picked out a complete bolt and carrier from the glass case and installed it in one of the 16" DPMS uppers and subsequently installed the complete upper on my Colt HBar via offset pin. He inserted the gauges in the chamber a couple of times and mucked around with it. After he was satisfied he showed me the go gauge and basically said it was good to go. Now he had lots of ARs and all the other tacticool guns on fairly big side-by-side tables. Judging by his professionalism he has plenty of experience with ARs since he was pretty busy installing the match triggers customers were buying. This guy checked with a no go and go gauge just to make sure all is fine, if that doesn't tell you something then you must be a gambling man. There are too many variables in the machining of the parts that deals with the AR's headspace. I can tell you one thing, if the chamber is a bit long it may fire most of the rounds without a problem, but just wait for that one case that doesn't like the long out of spec chamber and you may just be in for some fireworks. I suggest after you get your AR together to have a competent AR smith to double check to see if all is well. He shoudln't charge more than 20-30 bucks, I'm sure your safety is worth that much. josh
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Old December 1, 2007, 01:20 PM   #6
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I appreciate all the input, I probably wont spend $$$ on some gauges for a one time use (that could change depending on how much fun I have w/ my new BR)

Its seems like the chances are it will work no problem but, I'll have a qualified person take a look at it just to be sure

thefiringline forums have been bookmarked!
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