AR Upper Assembly

[pisgahrifle]

Thanks for the feedback, Chris. You caught me a shad to late, though- I'd already agreed to an Armalite. What can I say? It matched my lower!

So I've got to put a DPMS M4 barrel on this Armalite upper. After checking over my list (again) and getting another list made up of all the parts I forgot the first time, I think I'm ready to put this upper together.

Except for this tiny, teeny, miniscule, trivial thing.....

Will it blow up on me if I don't take it to somebody with a set of gauges and have it headspaced?

[John Dunn]

My most recent AR builds swallowed a .223 No Go gauge, but wouldn't take the field gauge. I wouldn't sweat checking the headspace, just shoot it.

[scottmilk9]

No need checking for headspace on an AR, unless the bolt doesnt close or anything funny like that. I wouldnt recommend switching bolts between uppers also. I've built my fair share of AR's and never had one where headspacing was an issue.

[pisgahrifle]

Okee Dokee...

I should have this thing thrown together by this weekend and have it shot Saturday. I'll let you know how many digits I've got left then.

[Patrick Sweeney]

If the rifle works, then it works. If the headspace is off, then you'll find out one of two ways: if it is seriously under, then the rifle will quickly stop when it gets grubby. If it is seriously over, then your reloaded brass will die after two or three loadings.

The problem isn't measuring it, it is correcting it if needed, after. Correcting out-of-spec headspace is easy in only one situation, but still expensive: an under-size chamber in a chrome-moly or stainless barrel. You ream it out. Everything else is much more expensive than a chambering reamer.

Sometimes it is better not to know, as long as the rifle works. (Ohmygod, did I just say that?) New-production bolts and barrels are much better in being correctly headspaced than in the old days. Most likely everything is fine.

[EricW]

Pat,

What's the solution to building one that's right out of the blocks? Buy a short-chambered barrel and ream it out in increments until it takes a GO gage?

[Patrick Sweeney]

Yes. Tell the barrel maker your intentions and they can probably supply one short by ten thou or so. While the "book" says to ream to a GO gauge, and accuracy will be best (I'm sure it is) most AR's I've shot worked best, and had no accuracy problems, when they were almost ready to swallow a NO-GO gauge. (By "best" I mean a rifle properly set up will run all day in anyone's class with only additional ammunition and lubricants to keep it running.)

I've measured brand new Colt rifles where you could get the locking lugs started, but couldn't close the bolt on a NO-GO gauge.

For best results, start short, and ream until it will take a GO gauge. Then practice and shoot it like a match rifle and see if it balks once it is dirty or hot. If it runs fine, leave it alone. If it starts to short-stroke, ream a bit more until it works 100%. Stop when you can almost get the bolt head to turn on a NO-GO gauge. If it is still balky then, headspace is not your problem.

[EricW]

Thanks Pat.

And you're right, Colt chambers are tight. I had to grind down the base of my 223 die to get my reloads to where'd they'd chamber nicely.