Hello all,

I'm just about to finish up my first AR15 build. The upper, barrel, BCG and bolt are from Palmetto State Armory and brand new.

Is it a good idea to check the head space on this build?

Thanks,
Steven

Nah. Checking head space is not necessary. The barrel is "pre" head-spaced during the manufacturing process and prior to being installed to the upper receiver. Effectively, the head-space is verified by the fact that it fits into the upper receiver. If it doesn't or if the M4 feed ramps (if it has them) don't line up, your barrel or receiver is out of spec. If you buy an upper receiver with the barrel already installed, then you are good to go. Otherwise, "if it doesn't fit, then its sh't."

As Pmeaster touched on, AR's head space is determined by the correct spacing, torquing and pinning of the barrel extension on the chamber-side of the barrel during manufacturing. Any properly machined AR bolt will head space correctly, unless it's damaged, or severely worn.

What they said.  

Make sure the bolt will close fully on a dummy cartridge if you have one.

When you get to the range, if you have a "sticky" bolt issue where the bolt will get stuck shut on a full chamber then you have an problem.

+1

If you don;t have those, get some. Magpul sells a 5 pack.

Often, a gas/cycling issue can look like a "sticky" bolt issue (from out of spec barrel extension). So have someone with some experience take a look at your weapon before you run off and replace your barrel/receiver. You may just need a lighter or heavier buffer.

Yes check before installing the barrel.
If there is a problem it can be easier to return it more ways than one.
The chances of getting a barrel/bolt that are significantly out on headspace are low.
I have found a number of barrel/bolts that failed the Go gage due to tolerance stacking with the bolts.
This is not normally a problem for the tolerance range factory ammo is normally made in.
However get ahold of a lot of ammo that is in the high end of the tolerance range and you can start having issues.
Not necessarily a big deal at the range, but could lead to unintended consequences in a HD situation.
Dummy rounds and such are not a substitute for headspace gages as they are made to an entirely different tolerance and purpose.

If you're talking about those Magpul plastic dummies .... forget it.

They really are a piece of crap and should never be inserted into a chamber unless you are practicing malfunction/jamming drills.

+1 I check every barrel before installing. I do not assume every barrel is checked by the manufacture. Sarcasm on, but you can try checking headspace with live ammo. If it shoots then it's ok, if it doesn't or KB's, then it would have failed on the NO-GO. Sarcasm off
Even the manufacturers suggest to check the headspace.

My local small town gunsmith gauged my build, and refused to charge me for it.  How much is peace of mind worth?

depends on who you talk to, ive done 2 a 16'' and a 7.5'', i use quality parts, did not check headspace, both rifles run like champs

Meh.

And there in lies the rub.  One of the reason for checking it is to make sure that bolt is in spec with your chamber.   You have no way of knowing without using gauges.  

 
This mythical set at the factory, in the barrel extension blows me away. Check it, don't check it....headspace is measured to the bolt face of the bolt you are using.  If it requires your bolt face IT CANNOT BE SET AT THE FACTORY IF THEY DIDNT HAVE YOUR BOLT.  

I check all mine. Ymmv but it's a good idea. I had three out of spec with multiple bolts in the last year or so.

for safety sake it wouldn't hurt to check............Ive seen new builds with all new parts close on a no go gauge.............its your call........

Just go buy yourself a Forster FIELD gauge or NO GO gauge...If the bolt locks up and you can pull the trigger DON'T FIRE THE GUN..Cheap insurance!

I agree with Lug1, I am a bit concerned by pmeaster post... It was my understanding that the bolt locking into the barrel extension/barrel created the chamber and this was where the headspace was determined.  This means you should be able to take just a barrel (with extension) and the bolt you plan to use and be able to check the headspace with just these two components... outside the receiver.  As long as you use this headspaced bolt+barrel combo your headspacing will be fine even after assembling into the receiver.  
Other things like an incorrectly installed barrel-to-receiver union could prevent the proper "chambering" of a round, but this does not change the headspacing.
I think some are confusing "checking headspace" with "small tolerance manufacturing" which produce interchangeable parts.  
Were the barrels checked at the factory for headspace using a benchmark bolt? Probably, but is that bolt exactly the same dimensions as your bolt... that is the question.  A large percentage of different manufacturer barrel+bolt combos will likely be within tolerance for proper headspace right out of the box, but not all.

Yes.  Do it to remove uncertainty and assure a safe rifle.

I always check my builds. 10 minute check for a piece of mind is well worth it.

anyone who says not to do it..........is playing with fire..........for safety sake at the least get a FIELD REJECT gauge..........I have seen new components that will close on a no go gauge............Unless the company you purchased everything from has confirmed they have headspaced and test fired the components.

Back in the late 80's when I first started building AR 15's I didn't have the tools to install barrels ......I used to take my work to a gunsmith........that always checked the barrels he installed with a "Field Reject" gauge..........Its a piece of mind.........and safety thing...........

This.  The barrel extension is machined to match a bolt that meets certain specs.  That machining can be off, or the bolt can be off, and you have headspace issues.  The only time you can get a barrel that has had the headspace checked is one that comes with a matching bolt.

Checking headspace with a new barrel tells you a couple of things.  It tells you whether your new barrel is safe with the bolt you're trying to use.  It tells you whether your new barrel's chamber is closer to "minimum", or if it's closer to "maximum" (which is essentially measuring whether your barrel "looks new" to the headspace gauge).  It also tells you whether your chosen bolt is a good match for that barrel.  

Both the barrel and bolt are required for headspace measurements, so if you gauge your new barrel and the bolt closes on a NO GO gauge, maybe it's the barrel, but maybe it's the bolt.  Bolts are cheaper than barrels, so rather than running a setup that has longer than ideal headspace (and stretching brass every time you fire it), try a different bolt to see if maybe the bolt is to blame.