Headspace

[prepare]

When should headspace be checked and with which gauges, go, no go, field gauge?

[mark5pt56]

I spoke with IG on this early in the year and he advised to just go with a Field gauge, I use the Colt one fro Brownells. (1.4736)

I would if replacing a bolt on a used upper
Switching a bolt from another
On a new build, maybe a GO as well just to make sure who ever made it will allow chambering and nothing excessive either.
If having a high round count upper to insure it hasn't worn to the point of unsafe


https://www.brownells.com/gunsmith-t...-prod6646.aspx

[titsonritz]

I spoke with IG on this early in the year and he advised to just go with a Field gauge, I use the Colt one fro Brownells. (1.4736)

I would if replacing a bolt on a used upper
Switching a bolt from another
On a new build, maybe a GO as well just to make sure who ever made it will allow chambering and nothing excessive either.
If having a high round count upper to insure it hasn't worn to the point of unsafe


https://www.brownells.com/gunsmith-t...-prod6646.aspx

Same here.

If excessive headspace, first replace bolt assembly and then recheck. If headspace is not corrected, replace barrel assembly; then recheck with the original bolt to determine if the bolt is still good or if the bolt should be replaced also.

[prepare]

I spoke with IG on this early in the year and he advised to just go with a Field gauge, I use the Colt one fro Brownells. (1.4736)

I would if replacing a bolt on a used upper
Switching a bolt from another
On a new build, maybe a GO as well just to make sure who ever made it will allow chambering and nothing excessive either.
If having a high round count upper to insure it hasn't worn to the point of unsafe


https://www.brownells.com/gunsmith-t...-prod6646.aspx

On the field gauge you referenced from Brownells, does it work like a NO-GO gauge? Meaning the stripped bolt should not turn?

[26 Inf]

Yes.

Here is what the TM says: ETA - Change 4 Page 3-47

6. Assemble charging handle assembly (4), bolt assembly, and key and bolt carrier assembly (5) into upper receiver assembly (6).

7. Insert headspace gage (7) PN 7799734 in chamber. Important to note that the gag PN7799734 does not require removal of the ejector because the rim is relieved to allow the ejector to remain uncompressed

For the purpose of this test "light finger pressure" is defined as 8 1/2 to 8 3/4 pounds.

8. Check headspace by pressing key and bolt carrier assembly (5) and charging handleassembly (4) forward using light fingerpressure.

9. Bolt should not rotate to locked position. Key and bolt carrier assembly (5) must protrude from rear of upper receiver assembly (6) for proper headspace. If excessive headspace,first replace old bolt assembly with an unused bolt assembly and then recheck.

[lysander]

If you do not have gauge, P/N 7799734, removal of the extractor may be required...

For the AR type barrel, the primary use for the GO and NOGO gauge are at the factory, in conjunction with a gauge bolt, to insure that the barrel and barrel extension are properly assembled. If you are the type that cuts his/her own chambers, then a GO and NOGO are essential. Otherwise, just a FIELD is necessary to check for wear.

Unless you have little confidence in you barrel or bolt manufacturer, not that there is anything wrong with that, it this case.

[prepare]

Thanks!

[Uni-Vibe]

I'm astonished that no commercial gauge maker has made one with relief, so we don't have to remove the ejector.

M4C machinists: why not buy some Colt ones and do the mod? I'd buy one if reasonably priced. I bet lots of other AR-heads would too.

[lysander]

I'm astonished that no commercial gauge maker has made one with relief, so we don't have to remove the ejector.

M4C machinists: why not buy some Colt ones and do the mod? I'd buy one if reasonably priced. I bet lots of other AR-heads would too.

Because most head spacing is done by gunsmiths in incomplete barrels and unassembled bolts.

The Army head space gauge (P/N 7799734) doesn't even have a extractor groove.