Headspacing.

[nub]

I have a stripped upper laying around, so I bought a Black Rain Barrel and a BCM BCG.... do I need to check headspacing or is it good to go?

[Xrugger2012]

My recommendation would be to contact the manufacturer to ensure that their barrels are pre-checked for correct 5.56 head spacing. Most of the reputable manufacturers do this. I personally would also like to gauge it myself since it is my face it could blow up in... just sayin. gauges are inexpensive, and can be had at brownells, a go and nogo gauge set is cheaper then buying a new gun.

[nub]

Thank you sir.

[AR-10]

Headspacing is set when the barrel extension is installed on the barrel.

In other words, put it together and shoot it.

[M. Gale]

Headspacing is set when the barrel extension is installed on the barrel.

In other words, put it together and shoot it.

Sing it brother...

[markm]

I glue shims on the barrel extension to tune head spacing!

(Just kidding.... this is a reference to an imbecile soaked barrel nut thread on M4c.)

[todd.k]

I'll take the other side.

The Mil has consistent suppliers, consistent QC, all parts are made to one print rather than reverse engineered, and the Mil manual still requires HS be checked if a bolt is replaced.

All our rifles and complete uppers are checked for proper HS before test fire. I expect most quality manufacturers do the same, so why give a pass to home builders? I know the odds are slim of there being a problem, but we do need to contain 55,000 psi here.

[MoxyDave]

I'll take the other side.

The Mil has consistent suppliers, consistent QC, all parts are made to one print rather than reverse engineered, and the Mil manual still requires HS be checked if a bolt is replaced.

All our rifles and complete uppers are checked for proper HS before test fire. I expect most quality manufacturers do the same, so why give a pass to home builders? I know the odds are slim of there being a problem, but we do need to contain 55,000 psi here.

Well said sir. I completely agree. Better safe than sorry, and it's cheap insurance. I always check the headspace on my builds.

[Eric]

It's possible to have a an in spec barrel w/extension, with an out of spec bolt, that could cause it to fail a gauge check. Not likely, but possible.

[nub]

Alright, thanks for all the information. Is there anything else to be concerned with after the build before I take it to the range?

[landshark]

Alright, thanks for all the information. Is there anything else to be concerned with after the build before I take it to the range?

I know that in my shop we always make sure that all of our weapons pass a PFI (Pre Firing Inspection) before heading out to a range. This includes a function check, HS and barrel straightness among other things. This is done because not all Marines are "nice" to there rifles (have seen them used for everything from legs of a hasty table to a hammer...) but for a home build a simple function check and HS are typically all that is needed.

[AR-10]

Makes sense if you are assembling uppers for customers, I've never bothered to check.

If I were putting together an upper with an unknown barrel/bolt, I would be more inclined to pick up some gauges but I don't typically buy components unless I know where they came from.

[John Hwang]

Every barrel with ship with bolts get headspaced. Why?? Believe it or not about 10-15% doesn't head space correctly even from the same MFG. Will it still work, sure (meaning, it will be safe to fire in most cases) but you will not get the best accuracy out of your weapon.

Head spacing is a simple term to measure the spacing between the bolt face & chamber. Too much space, the bullet can sit loosely, too little space, you can have cycling issues. There are head space gauges for each caliber. GO / NO GO / Field are the most common. Go is good, NO GO is loose but still safe & Field is dangerous to use. We've yet to test a new bolt or barrel to fail the field gauge but we don't deal with cheap barrels so YMMV. Some MFGs go even beyond that and have special gauges made so we can get the tightest fit possible building a supreme rifle. Also, gauges need to be replaced from time to time as they lose shape with testing.

[tim716]

Sorry to bring up this old thread but i'm on the fence about buying go/no go gauges for my headspace. I have the Rainier Arms NIB BCG and BCM 14.5 5.56 Barrel. All the people i've spoken to have said that they are both quality parts and they should be fine.

[GOST]

I'm running that same configuration on a rifle and mine is fine. It should be fine but if checking it would give you peace of mind then check it. Gauges don't cost that much.