Finishing my first complete AR15 build; headspace problems


PDA






1KPerDay
June 2, 2014, 05:11 PM
So I finally got all the parts together for my "cheap/light" build. I have assembled lowers before and stuff, but haven't installed any barrels to this point.

upper is a PSA flattop. Barrel is E.R. Shaw/Model 1 lightweight 16" CAR barrel from Midway, info says .223 chamber, reviews/feedback say .223 chamber.

BCG is "5.56 8620 with charging handle" from PSA. Not engraved with typical PSA logo so I assume it's no-name or generic brand. I don't know.

In any case, I'm having some trouble.

0. Crappy cheap Delton barrel nut sheared 3 teeth and was generally a PITA to install. That's another issue. I've learned my lesson on that one.

1. 8620 BCG closes on a Clymer .223 NO GO gauge. (1.4666"). The PSA BCG that came with my PSA mock dissy upper does NOT close on the NO GO .223 gauge in the new rifle. Both BCGs close on .223 NO GO gauge if tried in the PSA dissy upper (which has a 5.56 chamber).

So: I assume this means that my crappy 8620 BCG or bolt is out of spec, correct? OR, does it mean that in this particular combination, the chamber is actually 5.56?

I also assume that to confirm this I need to purchase a 5.56 NO GO gauge?

OR, can I assume that if the PSA dissy BCG doesn't close on a .223 NO GO gauge, it's close enough to a 5.56 chamber?

Wait, that doesn't make sense. That just means that it's a .223 chamber WITH THE PSA DISSY BCG, right?


Ugh... this has been a nightmare. 2012 was the wrong time to start buying parts and building ARs. Crappy NFA poly lower, crappy BGC, questionable (to this point) barrel...

If you enjoyed reading about "Finishing my first complete AR15 build; headspace problems" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
rcmodel
June 2, 2014, 05:33 PM
MAX 5.56 NATO is 1.4736".

Your .223 gage is 1.4666".

So you have about .007" to play with.

Scotch 'Magic' tape runs about .0015 per layer.
So two layers = .003", etc, etc.

See if more then 4-5 layers on your gage head will close.

Or buy some shim stock at the auto parts store.

rc

1KPerDay
June 2, 2014, 06:29 PM
Thanks, I'll check it out. I ASSUME that if I will close on a .223 No Go, but WON'T close on a 5.56 no-go (or equivalent), then the chamber is actually a 5.56? Or is it just the combination of this bolt with this chamber?

1KPerDay
June 2, 2014, 06:31 PM
BTW I've been checking with fully assembled bolt (with extractor/ejector). is there any reason I shouldn't? The book I've been following says use fully assembled BCG. But in reference to other rifles I've learned about they always say to strip the bolt before checking headspace.

highorder
June 2, 2014, 06:36 PM
I always remove the extractor (and ejector in your case) if possible.

I want to "feel" the lugs seating. ymmv.

BBBBill
June 2, 2014, 07:17 PM
Remove the extractor and ejector. They can provide a false sense of what your trying to measure. There's more to the difference between .223 and 5.56 chambers than headspace measurement. The leade is longer in a 5.56 chamber as well as the more generous headspace dimension. A headspace gage won't measure that. And a bolt carrier group won't change it from .223 to5.56 either. So use tape, shim stock, get the 5.56 no go gage, or buy the whole set of .223/5.56 gages to cover the entire spectrum if you're going to be doing much of this. That will help you with determining headspace. ER Shaw are not noted for screwing up a chamber, but stranger things have happened. Who knows what was done to it after it left their hands.

1KPerDay
June 2, 2014, 08:00 PM
Well the fact that the BCG won't close on a .223 no-go gauge with a "known good" BCG leads me to believe that the problem lies with the 8620 BCG. Right?

nulook45
June 2, 2014, 09:17 PM
Try just replacing the BOLT not the entire bcg and recheck

4v50 Gary
June 2, 2014, 09:18 PM
What BBBBill suggested. Remove the extractor and ejector or they'll give you a false reading. There is hope for your AR.

BBBBill
June 2, 2014, 09:45 PM
If it is bolt related it will only be the bolt. The bolt carrier will have zero effect on headspace. It is more common for barrels to be marked 5.56 when they are really .223. Far too many of the "hobby grade" AR parts manufacturers seem to not know the difference. Given your suspicions/concerns, why not do a chamber cast using Cerrosafe as well? That would confirm the barrel chambering and whether it is in spec for either .223 or 5.56. The chamber could be defective in other respects and still check out for headspace with a given bolt.

1KPerDay
June 2, 2014, 09:54 PM
What BBBBill suggested. Remove the extractor and ejector or they'll give you a false reading. There is hope for your AR.
Well since it closes on a no-go with extractor and ejector in place, I can't figure how it WOULDN'T close without them in place.

But I'm trying to locate a 5.56 NO GO or MAX gauge to be sure.

Actually probably cheaper just to buy a spare bolt. :rolleyes:

so much for cheap....

1KPerDay
June 2, 2014, 11:05 PM
Well, I guess good news: I added one layer of Scotch tape to the No Go gauge and it won't close now.

So I imagine that's within what most would consider safe tolerances, right? Somewhere between 1.466" and 1.4675"?

rcmodel
June 2, 2014, 11:11 PM
Sounds like it.

Test fire it, and check each fired case for a stretch ring inside the case with a L-bent wire or paper-clip.

If you can feel a stretch ring at all inside the case on the first firing of new brass, it ain't right.

rc

1KPerDay
June 2, 2014, 11:44 PM
Okay, thanks. I'll have to get the gas tube installed. Btw anyone have a cheap rear BUIS or old carry handle lying around?

1KPerDay
June 3, 2014, 12:43 PM
Never mind... ordered one, and a new barrel nut. :rolleyes:

My "cheap" build has now cost me quite a bit more than the "bargain ARs" I've seen in sales lately. Ah, well... the lessons learned are worth it. Right? RIGHT? :D

RussellC
June 3, 2014, 09:49 PM
Never mind... ordered one, and a new barrel nut. :rolleyes:

My "cheap" build has now cost me quite a bit more than the "bargain ARs" I've seen in sales lately. Ah, well... the lessons learned are worth it. Right? RIGHT? :D
Call me silly but I do! Think about how expensive school is these days, and you have a gun you know inside and out upon "graduation"

Russellc

triggerman770
June 19, 2014, 04:51 AM
your barrel should have come with the bolt it was headspaced with. Most do
and it should be stamped on the barrel what the chamber is IE: .223 or 5.56

1KPerDay
June 19, 2014, 01:01 PM
your barrel should have come with the bolt it was headspaced with. Most do
uh.... :uhoh:

Arizona_Mike
June 19, 2014, 01:52 PM
I've have done a bunch of builds including with a fluted Shilen .223 Wylde which retails over $600 and have never had a bolt included.

Ideally you want a stripped bolt but with the AR you can place the gauge under the extractor first. You should remove the ejector to get an accurate GO measurement but it will not give you a false positive NO GO.

Almost certainly you have a 5.56 chamber. Shim your existing NO GO gauge and check.

Mike

rskent
June 20, 2014, 05:51 PM
Yea, the only time I ever got a bolt with a barrel was from White Oak. I think it was an extra 50 bucks to have them
pick out a bolt and check the head space with it. Seemed like a good idea at the time. Not sure I would spend the money again.

If you enjoyed reading about "Finishing my first complete AR15 build; headspace problems" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!