Head spacing an ar-15.

[dbrown]

I'm fairly new in to ar-15s and do not know what or how head spacing an ar-15 goes.

 

[rcmodel]

You don't.

AR-15 bolts, barrel extensions, and chambers are headspaced at the factory.

If you buy a bolt & barrel assembly, it should already be correctly headspaced.

rc

 

[HOOfan_1]

Most I have read says only need to buy a "field" gauge. The "field" gauge measures the maximum allowable headspace.

There are others who may use Go and No-Go gauges.

The Go gauge ensures there is enough headspace. If the bolt won't close on the Go gauge, there is not enough headspace
The No Go gauge ensures optimum headspace. If the bolt closes on the No Go gauge, there might be too much headspace, go to the Field gauge, if the bolt closes on the field gauge then the headspace is beyond SAAMI specs and could be dangerous.


to check headspace on an AR, you need to remove the ejector from the bolt. The easiest way to do that is buy a jig to push the ejector in as you hammer out the roll pin which holds it in the bolt. There are videos on Brownell and Youtube.

EDIT:...my entire post deals with CHECKING the headspace, not adjusting it...

 

[briansmithwins]

Just a minor correction:

bolt must close on GO
bolt must not close on NO GO or FIELD
bolt is pushed forward with light finger pressure, not the recoil spring.

A USGI FIELD gauge will be relief cut for the ejector, so you don't have to strip the bolt.

I check headspace on all my rifles. Then again, I like seeing and already have enough scars.

BSW

 

[mljdeckard]

In my experience, this mostly became a significant concern because the military mixes and matches parts. If one bolt is more or less worn than the chamber it is being fitted to, the headspace and timing will be off. With new (IN-SPEC) parts going into new rifles, this is a very rare problem.

 

[rcmodel]

The easiest way to do that is buy a jig to push the ejector in as you hammer out the roll pin which holds it in the bolt.

A Mil-Spec bolt doesn't have a roll pin.

It is a solid pin, and you can just use a cartridge rim hooked on the extractor to lever down the ejecter spring and easily push the pin out using the tip of the firing pin.

rc

 

[HOOfan_1]

Mil-Spec or not, my Daniel Defense bolt had a roll pin and it took a roll pin punch and hammer to get it out.

 

[mljdeckard]

If I had a roll pin, I would replace it with the regular pin, I don't want to have to use tools to replace a broken extractor.

When I was trained, the extractor was part of a field strip. I understand now they don't want soldiers to play with it, because every lawn of every army post is full of lost pins, springs, and extractors.

 

[briansmithwins]

Just to make it clear: the EXtractor has a solid pin and is part of the standard field strip. The EJector has a roll pin and isn't normally stripped unless it's defective.

BSW

 

[madcratebuilder]

I find all the internet hysteria about head space and the AR15 amusing.:banghead:

The barrel extension is machined to a specification as is the bolt. I would bet you could not find a new bolt and new BE from any quality manufacturer that does not head space correct. Running a field gauge with a used bolt or BE is a good idea, but even then you have a 99%+ chance of correct head space. Even if it fails a field gauge it's not going to kaboom, it may split a case, but that's about it.

 

[taliv]

probably not new, but... several years ago i shot an AR15 until it was worn out and no longer passed the FIELD gauge test. I sold it for parts to a local after insisting repeatedly that he not fire it. A few weeks later I saw the same rifle in the local want ads described as "only 100 rnds fired".

THR's rules largely prohibit expressing my feelings about this individual, but reality is gunshows are chock full of people like him.

 

[HOOfan_1]

several years ago i shot an AR15 until it was worn out and no longer passed the FIELD gauge test.

any guess to how many rounds that was? How often did you check the headspace?

 

[taliv]

dunno. it was well-worn when i bought it. i think i put 15-20k ish rounds on it but it was 8 years ago so i don't really remember. i never kept a round count log on that one. i just remember buying 10k once fired brass and going through it a couple times

 

[medalguy]

Sounds like me. Over the years I've shot out a couple of barrels, replaced the barrels and bolts at the same time, never checked headspace, and went out shooting again. I've also built three or four AR rifles using all new parts and never had a problem with any of them.