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Posted: 12/20/2005 11:32:50 AM EDT
[Last Edit: 12/20/2005 11:33:31 AM EDT by JackalAR]
Finished my first build. Used a Sabre middy barrel and CMT BCG. Sabre of course recommends I at least get a go / no-go guage before shooting. Has anyone ever had a head space issue with new quality parts? I found some .223 guages (is this right for 5.56 chambers?) at Mid-South for $15 each, but seem to remember them being cheaper elsewhere and forgot where. If I go need to pick some up, do I need both go and no-go or??? How do I use them? Sorry for all the ?'s...thanks.
Link Posted: 12/20/2005 12:26:15 PM EDT
Link Posted: 12/20/2005 5:01:39 PM EDT
Uhhh...RTFM a few times and still don't know what guages to get. Says the Forster no-go is 1.467, but Military no-go is 1.473. Do I have to buy all three and hope for a tight chamber or what? Is it absolutely necessary to remove the ejector which requires a bolt vise does it not?
Link Posted: 12/20/2005 5:11:24 PM EDT
I'm obviously not going to say checking your HS is a BAD idea. But I just put together a new build with a new barrel from Denny's Guns. I'm not going to worry about it and plan on shooting it for the first time tomorrow!

Just my $.02.

Gundraw
Link Posted: 12/20/2005 5:25:16 PM EDT
Yea, just seems like such a small amount of tolerance though. Is the bolt and barrel the ONLY two parts that affect headspace? I would assume an MP checked CMT bolt and chrome lined CMV Sabre barrel would be GTG if these are the only critical parts. Do bolts vary that much between different ones of the same brand? Are they specifically checked for this as barrels are?
Link Posted: 12/20/2005 5:50:10 PM EDT
from Midways website:
"If the bolt closes on a GO gauge, then your rifle will accept any ammo that is within SAAMI specifications.

If the bolt closes on a NO GO gauge, the rifle chamber may have excessive headspace.

If a rifle closes on a FIELD gauge, the rifle chamber is dangerously close to or already over SAAMI specified maximum chamber size.

When chambering a new barrel, these gauges are invaluable to ensure a tight, safe chamber."
Link Posted: 12/20/2005 6:18:53 PM EDT
[Last Edit: 12/20/2005 6:19:54 PM EDT by JackalAR]
Seems like you'd need all three...a no-go would be the most versitle being that it's in the middle. How can you tell on an AR when the bolt is closed...when you can lock the lugs?
Link Posted: 12/20/2005 6:28:32 PM EDT
I would check to make sure it chambers a round, and locks...... then blast away.
Link Posted: 12/20/2005 7:38:33 PM EDT
Link Posted: 12/20/2005 8:15:49 PM EDT
Isn't a no-go for new barrels and field for rifles that have been in the field for a while?
Link Posted: 12/20/2005 9:03:16 PM EDT

Originally Posted By JackalAR:
Isn't a no-go for new barrels and field for rifles that have been in the field for a while?



Nope.
Link Posted: 12/21/2005 2:44:44 AM EDT
does it matter on what type of chamber it is...wydle chamber for example?
Link Posted: 12/21/2005 5:59:06 AM EDT
Again...how do you know when the bolt "closes" on an AR? I assume you remove the bolt from the bolt carrier? Is it a MUST that you remove the ejector / extractor?
Link Posted: 12/21/2005 7:02:01 AM EDT
Ok, I am prolly gonna get flamed... but I'll give my opinion anyway:


Originally Posted By JackalAR:
"Basically, unless you are installing new barrels, you don't need a "go", and even then, a factory cartridge can provide that (some would flame me on that one!)... "



This is correct. If the bolt will close on a factory cartridge... you dont have excessivley short headspace. That is what a go gauge checks for.


no go is nice to verify the condition of the firearm (hey, it passed a no go!)... field is likely the more useful for many surplus arms. I have all three for several calibers, and I have never needed or used the "go", but often use the field and no go...


Exactly. On a SAAMI spec rifle - a NO-GO is used to check if the chamber has excessive headspace. The bolt should NOT close on this gauge.

HOWEVER - AR-15's are NATO spec (or now Wylde, or a handful of other variations) chambers, not SAAMI. Military rifles are designed with a larger chamber spec (typically longer throat - to allow shooting higher pressure ammunition)

Therefore, it is common for a an new, in spec AR15 bolt to be able to close on a NO-GO gauge. Therefore - using a NO-GO gauge doesnt really tell you a lot. It might close, it might not.

The FIELD gauge is dimensionally closer to the max measurement we are looking for. If the bolt closes on a FIELD gauge, it is general accepted the rifle has excessive headspace, cause by a worn chamber, worn bolt, out of spec chamber, out of spec bolt, or improperly installed barrel extension. That being said - some rifles might even close and lock on a FIELD gauge, and that would not be a big deal to me.

The worst situation possible with the AR15 rifle is a tight chamber with high pressure ammunition... which is why I check to see if the bolt will lock with a factory cartridge. If it does, without having to slam it in the chamber, then I am good to go. The headspace is set at the factory by the smith who installed the barrel extension. It cannot be adjusted by you.... so really in checking headspace, all you are checking is did the manufacturer set it correctly. I have never heard of one being shipped out of spec.... though I suppose it is possible.



Again...how do you know when the bolt "closes" on an AR? I assume you remove the bolt from the bolt carrier? Is it a MUST that you remove the ejector / extractor?


You dont HAVE to remove the ejector or exctractor. Here is what I do.

Break open rifle at the pivot pin. Remove BCA and CH. Remove the firing pin from the BCA. Drop a round in the chamber. Insert the BCA, and with two fingers on the back of the carrier, push toward the chamber. It should snap around the extractor and the bolt should lock.

So understand if the bolt is locked or not - you really need to understand how the AR15 system works. Watch the bolt as you push the carrier. Look at the lugs on the barrel extension. The bolt, because of the cam pin in the BCA, will rotate as the carrier comes forward the last few millimeters. It "locks" when the carrier is fully inserted - and flush with the back of the upper receiver. You can see the bolt lugs have rotated and locked behind the extension lugs. This supports the bolt face as the back of the chamber, for firing.

For these reasons.... having a GO, NOGO, and FIELD set is never a BAD idea. If you were a true AR15 smith, they would be required. But for the average home builder, they arent necessary.

But I think you can see why some say "just get the FIELD gauge." Personally, I think if you are so obsessed with headspace in the AR system, you really should get all three... so you have some idea of exactly where your chamber sits.
Link Posted: 12/21/2005 7:17:29 AM EDT
[Last Edit: 12/21/2005 7:18:05 AM EDT by JackalAR]
Thanks man, cleared the mud for me, and saved me some money. I'll try the cartridge method. I understand now that I know you don't have to remove the bolt from the carrier. ...thought I was suppose to manually lock the bolt in or something.
Link Posted: 12/21/2005 10:18:22 AM EDT
Link Posted: 12/21/2005 10:35:30 AM EDT
Do you sell relieved field guages?
Link Posted: 12/21/2005 12:17:38 PM EDT
[Last Edit: 12/21/2005 12:21:15 PM EDT by Triple_D]

Originally Posted By Randall_Rausch:
More fun with headspace




Just to muddy the waters a little.....

Take a look at the dimensions on the Clymer 5.56 NATO headspace gauges.

Clymer 5.56mm NATO gauges:

-GO - @ .330" Datum - 1.4686"
- NO-GO - @ .330" Datum - 1.4746"
- FIELD - @ .330" Datum - 1.4786"


They are huge compared to the "military" gauge specifications. I've yet to find a bolt/barrel combination that would close on the GO gauge....much less the NO-GO or Field gauge.
Link Posted: 12/22/2005 11:42:14 PM EDT
Link Posted: 12/22/2005 11:43:40 PM EDT
Link Posted: 12/24/2005 6:27:02 AM EDT

Originally Posted By Randall_Rausch:
Are these dimensions marked on the gauges?
If not, what's your source for those dimensions?




The specs are not marked on their gauges, so I wrote to Clymer and asked them what the dimensions for both their 5.56mm and .223 Remington gauges are. Their .223 gauges have the same dimensions as the "civilian" gauges. But their 5.56 specs are different from anything else I've seen.
Link Posted: 12/24/2005 7:02:20 AM EDT
Link Posted: 12/24/2005 7:40:21 AM EDT
And they are not cheap either. LOL.

One day if I ever get rich, I may buy a set of these. That way, I'll have everything covered.

Time to go to work....
Link Posted: 12/26/2005 12:33:36 PM EDT
There are two things to worry about, too tight and too loose.

First, let's take care of too tight. Load up a couple of mags with good quality factory ammo. Cycle through your rifle by hand. Do they smoothly feed and eject? If so, you have sufficient headspace (not too tight).

Next, go shooting! Pick up YOUR brass and examine. Are the primers flattened (excessive pressure)? Now look just above the head (the "web" area). If headspace is excessive, this is the place where it will show up as stretching the brass. There will be shiny rings running around the circumference of the brass in that area. No shiny rings? Then your headspace is not excessive.

5.56 NATO and .223 chambers (Wylde and others) in the AR-15 are looser than .223 SAAMI chambers in bolt rifles to allow better chambering and extraction. This is on purpose, and not a defect. This is to allow dented or out of spec rounds to feed and eject smoothly.

So, if the new factory rounds will cycle through by hand easily, and the fired cases do not show the tell tale signs of stretching (and potential head separation issues), then you are good to go.

That's all there is to it.
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