Been looking all over for headspace dimensions for 5.56 chambered AR. I measured factory .223 with a Hornaday Headspace guage. 1.45". Just wondering what the minimum and maximum dimensions might be, and can I size on the longer side since the rifle is chambered for 5.56. Right now my resized brass is measuring 1.46". I can set the die a little lower to get 1.45" but it seems that I might be over stressing the brass.
Headspace Dimensions for 5.56 Chamber
- Thread starter Slinger
- Start date
- Status
rcmodel
Member in memoriam
Forget measuring.
Strip the AR bolt of the ejector & extractor, and try cases in the chamber itself.
Size only enough that you can feel only very slight resistance when manually closing the stripped bolt on a case.
That is the minimum for your rifle.
Not some magic number of what it is "supposed" to be.
Drawings:
http://www.ar15barrels.com/data/223vs556.pdf
http://www.ar15barrels.com/data/223-556.pdf
Headspace Guages:
http://www.ar15barrels.com/data/headspace.pdf
rc
Strip the AR bolt of the ejector & extractor, and try cases in the chamber itself.
Size only enough that you can feel only very slight resistance when manually closing the stripped bolt on a case.
That is the minimum for your rifle.
Not some magic number of what it is "supposed" to be.
Drawings:
http://www.ar15barrels.com/data/223vs556.pdf
http://www.ar15barrels.com/data/223-556.pdf
Headspace Guages:
http://www.ar15barrels.com/data/headspace.pdf
rc
Last edited:
rcmodel
Member in memoriam
I assume if he is measuring headspace, he is measuring to the imaginary datum line on the shoulder.
That's the only place a 1.45" measurement could come from.
1.4380" is to rear of shoulder.
1.5573" is to front of shoulder.
rc
That's the only place a 1.45" measurement could come from.
1.4380" is to rear of shoulder.
1.5573" is to front of shoulder.
rc
According to the standard diagram in the reference book, headspace for .223/5.56mm is measured where the shoulder in the chamber is 0.330" diameter at 1.467" from the bolt face. That's the 'datum' rc model was talking about. Your cartridge case can be slightly smaller than that, but not larger.
I've noticed other modern cartridges use such a datum, and that's how my go/nogo/field headspace gauges are made. Instead of trying to land flat on the whole cone of the shoulder, they land on specific point on the shoulder in the chamber.
I've noticed other modern cartridges use such a datum, and that's how my go/nogo/field headspace gauges are made. Instead of trying to land flat on the whole cone of the shoulder, they land on specific point on the shoulder in the chamber.
MCK45ACP
Member
A question to ants post. What reference book are you speaking of pertaining to the .330 dia. datum? I have been looking for this information and is difficult to find. I came across this site and this thread in a google search and I am quite glad I did. Thanks.
MCK45ACP
Member
I would also think that there is a formula to determine the datum dia. Does anyone know of that?
Clark
Member
The 223 headspace is at .330" diameter ring on the shoulder.
It is 1.4636" min 1.4736" max.
I have a 223 go gauge that is close to the 1.4636" and that is what I try to chamber to.
It is 1.4636" min 1.4736" max.
I have a 223 go gauge that is close to the 1.4636" and that is what I try to chamber to.
MCK45ACP
Member
I also use a Go gage at 1.4636. I am looking for the book that determines the datum dia. Not just for 5.56 but also other calibers such as .308.
Clark
Member
This book has most of what you seek.
http://www.amazon.com/Handloading-William-C-Davis/dp/0935998349
It does not have this, a 40 S&W or a 260 Rem, or anything after 1980.
But most cartridges were SAAMI registered before 1980 and the drawings with dimensions and tolerances for cartridge and chamber are in the back of that book.
You can buy the drawings from SAAMI, but that would be a more expensive route.
MCK45ACP
Member
Thank you Clark. I guess I failed to see the forest through the trees. I purchased that book back in 1982 and has been sitting there in front of me all this time. It has the info I have been looking for. I also suffer from analysis paralysis on occation. :banghead:
Innovative
Member
Headspace for reloaders vs. barrel installation
Slinger .....
When you measure your cases, you're only getting half the story. That information is only meaningful if you also know the exact size of your particular chamber.
The real concern for handloaders is the "difference" between those measurements. Check out my Digital Headspace Gauge, and see what you think. It works on ALL different calibers, and it displays actual chamber clearance (at the shoulder) by comparing your handloads to one of your fired cases. That way you can set your die height perfectly.
Slinger .....
When you measure your cases, you're only getting half the story. That information is only meaningful if you also know the exact size of your particular chamber.
The real concern for handloaders is the "difference" between those measurements. Check out my Digital Headspace Gauge, and see what you think. It works on ALL different calibers, and it displays actual chamber clearance (at the shoulder) by comparing your handloads to one of your fired cases. That way you can set your die height perfectly.
- Status
