Check Headspace on AR-15
Hello, which gauges do i need and how do i complete the check? I know AR barrels are headspaced but want to check to be sure..thanks
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Be sure and get the correct headspace gauges. There are two different types. 223 for commercial bolt action sporting rifles, and 5.56 X 45 for semi-auto AR type rifles.
I would imagine that the big on-line retailers who deal in AR parts in a big way, like Brownells and Midway sell the 5.56 X 45 type headspace gauges that you need for your AR.
Brownells has on-line video tutorials, you might check if the have one regarding headspacing AR's. U Tube also has a lot of tutorials.
You best be all full careful of the stuff on U Tube though. Lot of the folks who post their videos, don't know their rectums from a hole in the ground, and are just attention whores.
EDIT #1, I might be wrong on this, as it's been awhile since I built my AR. Believe that the instructions I followed at the time stated that you had to use AR specific headspage gauges. As the .223 gauges used for BA rifles wouldn't work and give erroneous readings.0 -
I use Bushmaster's gauges, don't forget to take the extractor off your bolt before you check the head spacing. 
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quote:Originally posted by shilowar
I use Bushmaster's gauges, don't forget to take the extractor off your bolt before you check the head spacing.
How can those gages be marked both 5.56 AND .233?? There close, but isn't there about a .004" difference between a nogo for each of them??
I never buy gauges from the company that makes the rifle I want to check.[;)] seems like asking a used car salesman if the oil was changed on schedule.[:D]0 -
quote:Originally posted by babun
quote:Originally posted by shilowar
I use Bushmaster's gauges, don't forget to take the extractor off your bolt before you check the head spacing.
How can those gages be marked both 5.56 AND .233?? There close, but isn't there about a .004" difference between a nogo for each of them??
I never buy gauges from the company that makes the rifle I want to check.[;)] seems like asking a used car salesman if the oil was changed on schedule.[:D]
They are the same case dimensions, but where the chamber's differ, are in the throat.
The 223/5.56x45 head space gauges are the same, as the distance being measured/checked is from the face of the bolt to the fulcrum of the shoulder. That is how all rimless, bottleneck cartridges headspace.
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quote:Originally posted by tsr1965
quote:Originally posted by babunOriginally posted by shilowar
How can those gages be marked both 5.56 AND .233?? There close, but isn't there about a .004" difference between a nogo for each of them??
They are the same case dimensions, but where the chamber's differ, are in the throat.
The 223/5.56x45 head space gauges are the same, as the distance being measured/checked is from the face of the bolt to the fulcrum of the shoulder. That is how all rimless, bottleneck cartridges headspace.
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I'll give you both a point [8D], as you are both correct
There a dimensional difference in the length, BUT there is also a difference in the datum circle diameter. Larger circle, shorter length to circle - smaller circle longer length. When you do the math however, both points are on the same shoulder angle.0 -
quote:Originally posted by Tailgunner1954
quote:Originally posted by tsr1965
quote:Originally posted by babunOriginally posted by shilowar
How can those gages be marked both 5.56 AND .233?? There close, but isn't there about a .004" difference between a nogo for each of them??
They are the same case dimensions, but where the chamber's differ, are in the throat.
The 223/5.56x45 head space gauges are the same, as the distance being measured/checked is from the face of the bolt to the fulcrum of the shoulder. That is how all rimless, bottleneck cartridges headspace.
Best
I'll give you both a point [8D], as you are both correct
There a dimensional difference in the length, BUT there is also a difference in the datum circle diameter. Larger circle, shorter length to circle - smaller circle longer length. When you do the math however, both points are on the same shoulder angle.
I hate it when math gets in the way[:D]
Comes out to only .001 difference.
http://www.ar15barrels.com/data/223vs556.pdf0 -
There was a guy here who checked the headspace on his AR.
His chamber was noticeably long, so he freaked out and demanded a new barrel from the maker. Too bad the replacement with tight headspace was not as accurate as his old "sloppy" one.
The original was kind of a freak, as Jeff Cooper said of one of his Scout rifles, if it was half as accurate, it would still be twice as accurate as necessary.0 -
quote:Originally posted by tsr1965
quote:
How can those gages be marked both 5.56 AND .233?? There close, but isn't there about a .004" difference between a nogo for each of them??
I never buy gauges from the company that makes the rifle I want to check.[;)] seems like asking a used car salesman if the oil was changed on schedule.[:D]
They are the same case dimensions, but where the chamber's differ, are in the throat.
The 223/5.56x45 head space gauges are the same, as the distance being measured/checked is from the face of the bolt to the fulcrum of the shoulder. That is how all rimless, bottleneck cartridges headspace.
Best
what he said0 -
deerhntr,
Please don't take this wrong as I don't mean to diminish your question or the fact that you're seeking information. But...
If you don't know the process of checking the headspace nor the parameters of the headspace in an AR15, how are you supposed to know if you're getting the right answer?
Headspace in an AR platform barrel is the same as headspace in a Bolt Action rifle in that the headspace dimension for an AR15 is from the bolt face to the datum line of the shoulder of the chamber as shown in the photograph below. The difference is how we arrive at that dimension.
Before cutting a chamber, we usually measure the headspace by holding the extension in a padded vise and insert the stripped bolt into the extension from the bottom, rotating the bolt until it rests on the lugs in the extension. We use a depth mike to measure from the face of the extension down to the bolt face which is the actual headspace dimension for cutting the chamber. Here's the difference though. We will use a +0.002" headspace gauge instead of the standard gauge which allows for the feeding and operation of this semi-auto rifle system. The gauge sets we use consist of 11 Match precision ground gauges in 0.001" increments (+8/-2 and the standard gauge) with a retail of between $250 and $350 per set.
Now, with your rifle already assembled and headspaced, you will have to remove the barrel from the upper, remove the bolt carrier group, disassemble the bolt from the group and then strip the bolt. Holding the barrel in a vise you will insert a gauge into the chamber then fit the bolt into the extension and rotate it in an attempt to feel the gauge against the bolt face. If you don't feel a slight resistance, a longer gauge will be tried. When you can't insert the bolt and rotate it against a gauge you have gone too far. The headspace is the gauge before the stoppage.
The standard headspace for AR platforms is usually a +0.002" to allow the rifle to feed and function. Headspace held tighter will usually result in malfunctions. If your rifle feeds and functions, I'd leave well enough alone. There are too many other factors which affect accuracy besides headspace and I doubt you will be able to do any of the diagnosing.
Best of Luck with your endeavor!0
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