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View Full Version : Assembling AR-15 Upper Headspace... Adjustment?


Just-in
03-04-2012, 7:34 PM
After much procrastinating It seems the best route to get what I want for my latest AR is to assemble my upper. I want to use a DPMS 18" barrel. If once I have everything assembled my headspace is not to spec how can I adjust it? Or with new parts am I pretty much safe? Am I better off going with a matched set of a bolt and barrel?
Thanks

LAL6
03-04-2012, 7:52 PM
The only adjusting you can do is by buying a different bolt. If you are buying all new parts it should be good to go, some dealers will check headspace for you if you buy barrel/bolt together.

Its not recommended to use an old bolt with new barrel AFAIK

LAL6
03-04-2012, 7:53 PM
sorry double post

bohoki
03-04-2012, 9:28 PM
generally if the barrel has the extension installed and front sight attached the job has been done

707electrician
03-04-2012, 9:36 PM
The only way to change the headspace on an AR is to reset the barrel extension or machine the bolt. If you buy your barrel and bolt from the same place they can usually get you a matched bolt that has correct headspace

joelogic
03-04-2012, 10:35 PM
The barrel extension only goes on at 12 0'clock and if you machine the bolt then only that bolt will work. You can remove material from the breech face so any in spec bolt will work. But generally parts fit together.

The only way to change the headspace on an AR is to reset the barrel extension or machine the bolt. If you buy your barrel and bolt from the same place they can usually get you a matched bolt that has correct headspace

CHS
03-05-2012, 9:10 AM
AR barrels and bolts are headspaced at the factory.

Don't worry about it.

ScottsBad
03-05-2012, 2:09 PM
AR barrels and bolts are headspaced at the factory.

Don't worry about it.

I don't know what this "moderator" is talking about. It is kind of an irresponsible statement.

If you are assembling a rifle you really must check the head space. Most likely everything will be OK, but if not you could have a dangerous situation.

Consider this; Around 40,000 pounds of pressure are created in the chamber when a round is fired. If the bolt is not engaged properly you could have a serious problem.

If someone tells you "not to worry about it" don't listen. At least be smart and check it.

Cheers---

bohoki
03-05-2012, 2:26 PM
I don't know what this "moderator" is talking about. It is kind of an irresponsible statement.

If you are assembling a rifle you really must check the head space. Most likely everything will be OK, but if not you could have a dangerous situation.

Consider this; Around 40,000 pounds of pressure are created in the chamber when a round is fired. If the bolt is not engaged properly you could have a serious problem.

If someone tells you "not to worry about it" don't listen. At least be smart and check it.

Cheers---


yes it is possible to buy bare barrels and extensions and some goober could attach the 2 and sell the unit at a gunshow and if they screwed the barrel in too far the bolt wont lock and probably wont even go off if it is too far out then it could blow the case in twain due to the unsupported area

but if you buy a complete barrel assembly from a reputable source it is probably fine since the first thing they do is properly attach the barrel extension then only when that is done do they attach the gas block

so i guess its possible for goober to bodger together a barrel ramdomly screwing on the extension then drilling the front sight pins in and selling it at a gun show so be careful out there

and any normal person who buys a barrel without the gas block installed is crazy or a glutton for punishment since the cash savings vs labor required to complete the job is not much

CHS
03-05-2012, 2:49 PM
I don't know what this "moderator" is talking about. It is kind of an irresponsible statement.

If you are assembling a rifle you really must check the head space. Most likely everything will be OK, but if not you could have a dangerous situation.

Consider this; Around 40,000 pounds of pressure are created in the chamber when a round is fired. If the bolt is not engaged properly you could have a serious problem.

If someone tells you "not to worry about it" don't listen. At least be smart and check it.


Tell me again how much you know about AR's? Please.

First off, you can't even GET a set of 5.56 headspace gauges.

Second, AR barrels are HEADSPACED AT THE FACTORY during installation of the barrel extension. The extension sits in the receiver and receiver-to-extension or receiver-to-barrel fit DOES NOT CHANGE OR AFFECT HEADSPACE. At all.

Third, AR bolts are HEADSPACED AT THE FACTORY to headspaced reference barrels.

When you buy an AR barrel it comes headspaced. When you install it, nothing you can do will affect headspace.

Which is why you DONT HAVE TO WORRY ABOUT IT.

707electrician
03-05-2012, 2:58 PM
The barrel extension only goes on at 12 0'clock and if you machine the bolt then only that bolt will work. You can remove material from the breech face so any in spec bolt will work. But generally parts fit together.

The barrel extension can be installed in any direction before the gas port is drilled

russ69
03-05-2012, 3:06 PM
...First off, you can't even GET a set of 5.56 headspace gauges....



http://forsterproducts.com/catalog.asp?prodid=700597 max
http://forsterproducts.com/catalog.asp?prodid=700596 min

BAGunner
03-05-2012, 4:37 PM
http://forsterproducts.com/catalog.asp?prodid=700597 max
http://forsterproducts.com/catalog.asp?prodid=700596 min

According to the info here (http://www.ar15barrels.com/data/headspace.pdf) by ar15barrels

That max gauge is a field gauge: 1.4736"
The no-go gauge is 0.003 smaller: 1.4706"

BAGunner
03-05-2012, 4:50 PM
Second, AR barrels are HEADSPACED AT THE FACTORY during installation of the barrel extension. The extension sits in the receiver and receiver-to-extension or receiver-to-barrel fit DOES NOT CHANGE OR AFFECT HEADSPACE. At all.

Extension screws onto barrel, that changes headspace. This has nothing to do with upper receiver.


Third, AR bolts are HEADSPACED AT THE FACTORY to headspaced reference barrels.

When you buy an AR barrel it comes headspaced. When you install it, nothing you can do will affect headspace.

Which is why you DONT HAVE TO WORRY ABOUT IT.

If you buy the bolt and barrel w/ extension from the same place, it will be headspaced. If not, you best hope is that both the bolt and barrel w/ extension is manufactured within tolerance, so that when they mated together, the headspace is still within spec.

That's why buying from reputable manufacturers is important.

CHS
03-05-2012, 4:58 PM
Extension screws onto barrel, that changes headspace. This has nothing to do with upper receiver.


And that is exactly what I just said.


If you buy the bolt and barrel w/ extension from the same place, it will be headspaced. If not, you best hope is that both the bolt and barrel w/ extension is manufactured within tolerance, so that when they mated together, the headspace is still within spec.


It doesn't matter if you buy the bolt and barrel from different sources. Any decent manufacturer from DPMS on up to Colt, Noveske, Larue sells factory headspaced bolts and barrels.

What part of "It's done at the factory and you don't need to worry about it" do you people just not get?

Lets put it another way:
How often do you hear stories about people getting factory-new AR barrels and bolts that WERENT headspaced properly?

supersonic
03-05-2012, 5:24 PM
OP - If it really has you concerned and you are ever up here in my neck of the woods, I have a set of 5.56 headspace gauges that I can check your rifle with. Keep it in mind.;)

BAGunner
03-05-2012, 6:49 PM
Also don't mix new barrel w/ old bolt (or vice verse) without checking the headspace first. The chamber will grow 0.001 longer in the first several hundred rounds, and another 0.001 for the rest of the barrel's life.

Just-in
03-05-2012, 7:27 PM
OP - If it really has you concerned and you are ever up here in my neck of the woods, I have a set of 5.56 headspace gauges that I can check your rifle with. Keep it in mind.;)

Thank you and everyone else as well for helpful information. I'd pretty much gathered previously that using new parts there isn't a large likelyhood that the headspace will be out of spec. I understand the basic principles but not much more than that for the time being.
I wasn't certain as far as adjusting it if you'd have to machine the bolt face or adjust the barrel extention however It didn't click in my head that the extention is oriented with the port for the gas block so moving the extention to adjust headspace would throw everything out of whack...

All makes sense now thank you.
now where is my tax return check...:cool: