Finished assembling an AR--15 (5.56). I bought a completed upper assembly, and I am using a Midwest Industries BCG. Should I get a headspace check?

I can't say without knowing the brand of the upper. It if it's all quality parts I'd say no. But if i5 makes you feel better get a field gauge and check it.

I emailed aero precision about this. They said all there uppers are headspaced. They said it never hurts to do a field check though.

Your bolt could be off, unless it came with the rifle and aero headspace it.

just get this for peace of mind: http://www.brownells.com/gunsmith-tools-supplies/measuring-tools/headspace-gauges/5-56mm-maximum-headspace-gauge-prod6646.aspx

It's your gun, but I just use a loaded cartridge.  If it goes bang we GTG ;-)

That's probly the worst advice I have ever heard. It's not tight headspace that'll get you. Excess headspace. Huge potential to a kaboom with excess headspace.

You should.  Truth be told.  Most people who build their own don't.  Many talk a big game about safety but don't follow it.  

I have not had one of mine fail a field gauge which is what you need to check it with.

Tens of thousands of AR's are assembled without a headspace gauge check. It is NOT a standard manual action arm with pressed barrel in a trunnion requiring the bolt be installed to assemble correctly.

Just go shoot it. Check the first round for overpressure, stretching, cracks, etc. AR's assembled from components that came from opposite ends of the country are built and shot every day. Kabooms are extremely rare - recently the majority are guns with .300BO stuffed in the chamber. Odds right now are that will be a bigger danger.

Eight years ago this forum made fun of people who bought a headspace gauge, now it's the opposite. Unless you have a serious issue with closing the bolt on standard ammo, checking for headspace by the legion of previous assemblers wasn't done. And those guns are not yet blowing up.

Me? I bought a matched headspaced  BCG and barrel from my 6.8 supplier because the package was cheaper than separate parts. If headspacing is a concern then that needs to be addressed when you purchase it. Later in the game? They don't sell bolts sized over or under . . . and changing the barrel extension for a few thousandths more means you are better off buying another one. Don't buy cheap is your best insurance - but it's still no guarantee. Only their CS is.

This

I have tested only 3 ARs, and one of them failed with excessive headspace.  I was one of those who doubted if I needed to test headspace since I was buying very high quality components from very reputable manufacturers, but the truth be known, even the best can let something slip through.  If you're going to assemble rifles, you should invest in gauges, or have a gunsmith check it before you shoot it.  I would hate for one us in this great community get hurt.

Opinions are like....well you know.... ;-)

Huge potential to kaboom???  C'mon!

Insane advice..............Pick up any Government Depot manual on M16 maintenance, always check headspace .......when doing a re-barrel or replacing components....................for safety sake..................and piece of mind and FACE!!!!

You do realise the rnd is gonna fit with excess head space right? Given enough excess head space it will kaboom. It's nots a tight chamber that won't chamber ammo that's gonna get you. It's the super sloppy .015 over no go gauge chamber that's gonna pop in your face. Just cause it chambers ammo doesn't mean it's right.

I'll take my chances, thank you.

Fire a round, inspect the case, repeat as necessary or desired.  

Have a nice day.

$24 for a Field gauge from Brownell's.....
$30 for a MIN gauge from eBay........
$15 for a bolt disassembly tool from ARFCOM....

Peace of mind that components are within spec and gun won't blow up.....  PRICELESS!

I'm interested in this. Where can I get a bolt disassembly tool for $15 please?

Gun smith at local range checked mine for $10 and about 87 seconds of his time. It was worth it to me.

Here is that which you seek.