AR headspacing
I have heard of headspacing but not sure how it's done. Can anybody go through the theory of it for me? What is it? How do you do it? When do you do it? I just never got into that area to deep.head spacing, get your mind on the ball!!! and out of the gutter
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AR headspacing is set by the basic design. If the parts are 'in spec', and the barrel extension seated all the way forward, then the boltface will be at the correct distance from the chamber shoulder* when the bolt head is locked in position.
Adjustment involves trashing the out of spec part (if you can determine which part it is), and replacing the bad part with a new one.
You can order barrels with different chamber dimensions, but the barrel designer will rely on the standard bolt head and extension dimensions when working up the chamber profile.
No receiver involvement, here. AR headspacing involves the relationship between the barrel, barrel extension, and the bolt head.
See
http://www.youtube.com/watch?v=UfDgF0txAlE
Hope I helped. Joe
*that's what headspacing is. It's the distance from the boltface to a datum. In your case, the datum is the chamber shoulder. I've restricted my reply to the firearm you have asked about. There are many ways to adjust headspace, but it is not germaine to the AR type rifle.0 -
Pistollero1050,
Headspace is the dimension from the bolt face to the chamber feature which stops the forward motion of the case. In this example of the AR or any other .223 Rem/5.56x45 chamber, it's the datum diameter on the shoulder with a specified diameter.
Forster commercial .223 Remington headspace gauges (length to datum) are:
1.464" Go
1.467" No Go
There is also a longer 'Field gauge' which is the reject point for the military (5.56x45).
However, this gauging is usually for bolt action rifles and not semi-auto or full auto rifles. With AR15/AR10 platforms the headspace is allowed to be slightly loose (approx. 0.001" to 0.0015") to accommodate feeding from the magazine. Tight chambers and exact headspace will cause an AR platform to malfunction. Reloaders have to take this into account when full length resizing or small base resizing their brass.
Measuring the headspace in an AR15 is best left to a gunsmith with the experience and measuring tools to perform the task.
Here is a reasonable article to give you another look at the topic:
http://www.zediker.com/articles/AR_chambers.pdf
Best.0 -
Thanx guys, the reason I asked is I want to get another upper and use the bolt and carrier from my present upper. don't see why I can't do that except I read some where that this is not a good idea. 0 -
Pistollero1050,
You can use the carrier but the bolt and extension should be integral with the sale of the barrel to assure proper headspace.
Best.0 -
It might depend on how much your bolt has been used. I've bought several uppers w/o a bolt and supplied a new bolt which works fine. A used bolt with some wear on the lugs might not provide proper headspacing. In theory, a combination of new mil-spec parts should result in a satisfactory headspace. 0 -
you see alot of uppers that come without the BCG. I hear what is being said. Ordered a head space gauge from brownells. I figure I can measure and know the speces and make my decisions from that. I expect to have to do this more than once or twice. so knowledge is king.[;)][8D][:D] 0 -
I use the same bolt and carrier in three 223 and one 6mmx45 uppers.
Mil spec ARs have hard chromed bolts and hard chromed chambers and bores so headspace dimensions aren't going anywhere for a long time.
It wouldn't hurt to check fired cases anyway.
If you're into competitive target shooting you might want to get a set
of gages and set up for minimum headspace.0 -
I question why one would not spend a few bucks and have more than one BCG for 4 uppers. I keep a couple of new extra BCG's just in case I break an extractor or something. 0
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