Gauging questions on an AR 15 upper assembly.

[MAHLMAN]

OK I have what is supposed to be a Palmetto upper. I have bought a set of go nogo gauges to try and start being more meticulous about what I have bought before I shoot them. So putting the go gauge in the chamber and putting the BCG in battery it is flush with the end of the upper reciever. The problem is the No Go gauge does the same thing. Now I have a Wilson upper here and the go gauge works with the BCG in battery and the end is flush with the upper. The No Go however does not allow the BCG to go into battery and the BCG extends past the end of the upper reciever. In the mean time I also took the barrel off and cleaned things and used some of that Mil Spec moly grease for reassembly and torqued to 50 lbs. I am not real impressed with the kind of cheesy aluminum barrel nut and how the handguard mounts to it.

How do I determine if it is the bolt, BCG or barrel to receiver fitup that is the problem? I don't mind getting tools and gauges to figure this out I just don't want to jump in and start buying things without a reason to do so though.

 

[Jgault]

Are both the uppers 223 or 5.56? If so what gauge are you using ? There is a slight difference between the two, so if one rifle is 5.56 and one is 223 that would explain your results, chambering a no-go guage isn’t really how it should be used, it’s used with the barrel removed using the bolt. Are you using a field gauge or a actual No-go gauge?

 

[msgriff]

I'm a bit confused. Headspace has nothing to do with the upper or barrel nut. In fact, many will check headspace before the barrel is installed so you don't have to disassemble it if the barrel is chambered incorrectly (rare on a AR-15 .223/5.56).

 

[TonyTheTiger]

I'm a bit confused. Headspace has nothing to do with the upper or barrel nut. In fact, many will check headspace before the barrel is installed so you don't have to disassemble it if the barrel is chambered incorrectly (rare on a AR-15 .223/5.56).

Same, I read it a few times and hoped someone would come along that understood it better than me. The carrier also has nothing to do with headspace.

 

[loveha]

Also headspace should be checked with bolt completely disassembled.

 

[357Max]

OK I have what is supposed to be a Palmetto upper. I have bought a set of go nogo gauges to try and start being more meticulous about what I have bought before I shoot them. So putting the go gauge in the chamber and putting the BCG in battery it is flush with the end of the upper reciever. The problem is the No Go gauge does the same thing. Now I have a Wilson upper here and the go gauge works with the BCG in battery and the end is flush with the upper. The No Go however does not allow the BCG to go into battery and the BCG extends past the end of the upper reciever. In the mean time I also took the barrel off and cleaned things and used some of that Mil Spec moly grease for reassembly and torqued to 50 lbs. I am not real impressed with the kind of cheesy aluminum barrel nut and how the handguard mounts to it.

How do I determine if it is the bolt, BCG or barrel to receiver fitup that is the problem? I don't mind getting tools and gauges to figure this out I just don't want to jump in and start buying things without a reason to do so though.

If I'm understanding correctly?

You have a Palmetto upper that chambers both the go & no go guage.
Your Wilson chambers the go, but not the no go.

First off you need to remove the roll pin from the bolt that retains the ejector/spring & remove them. The exception to this is if you somehow managed to purchase one of the special guage sets that are machined to clear the ejector (doubt it).

The gauges that do not require removal of the ejector look like this.

Do the above to both bolts and confirm your original findings.

As was stated earlier you don't need the barrel installed. You typically just use the bare bolt in the loose barrel. You can use the disassembled bolt in the carrier if the barrel is already installed though.

Sounds like you did, but make sure the chamber/lug area is clean.

Now recheck the Palmetto with the no go. If it closes without resistance then add 1 piece of clear scotch tape to the back of the guage. If it still closes add another. Each piece of tape is an additional .002" If you are able to close with 2 pieces of tape then your beyond the Field guage & it should be considered unsafe. Go gauge for 5.56 = 1.4646, No-go gauge = 1.4706” + .002" x 2 = 1.4746", & Field gauge = 1.4736”

Now use the Palmetto bolt in the Wilson barrel. If it will not close on the no go then you know it's the Palmetto barrel with the loose head space issue. If it does close on no go, but takes say 1 less piece of tape. Then you know the Wilson barrel is .002" tighter + approximately .004"-.006" lies in the Palmetto bolt.

All I ever buy is the go gauge & then I add tape if needed to figure out exactly where I'm at. Saves some money if you have a bunch of calibers.

 

[strikeeagle1]

You can turn down the diameter of standard headspace gauges on the lathe. I found that ~0.200" works well.

 

[MAHLMAN]

To reply to some of the comments now and the rest later tomorrow. Both barrels 5.56 Nato.

I thought I remembered reading somewhere that the relationship of the receiver to the barrel could effect head spacing. Maybe I remember this wrong.

I need to make an ejector removal tool before I do some of the comments and get a smaller punch to remove that pin with. Did not happen to have needed tools on hand to do this.

@357Max is right on the money for what I am trying to do. I do have the Forster 1.4636 223 go NATO minimum and the 1.4666 Forster 223 no go set. Somewhere around here I also have that 1.4646 one SOTAR recommended but I guess it is in the same place as my lost key set as I can't find either. Now if I cut down the gauges as strikeeagle suggests that will allow me to test the headspace without disassembly, right?

@strikeeagle1 that is an excellent idea. Even though I own a TL2 and VF4 the idea of cutting the gauges down just did not occur to me. Making the bolt extractor pin remover was on for today or tomorrow so I will be good to go on both soon. I will probably just buy gauges as I am only worried about 223 and 308 or maybe it should be 223 and 5.56 and 308 and 7.62.

So this brings up another question. Adding the lone Wilde barreled Larue upper I have to the mix is it required to have gauges for all three types?

 

[TonyTheTiger]

So this brings up another question. Adding the lone Wilde barreled Larue upper I have to the mix is it required to have gauges for all three types?

No. A headspace gauge only takes the chambers shoulder location into account, since that's what almost all bottleneck cartridges headspace off of. The difference between 5.56, 223, and 223 Wylde is all in the throat, where the bullet enters the rifling, and has nothing to do with headspace. The chamber as it relates to the case body area is identical between them.
Also, and I'm not trying to be a dick at all, but all the gauges and SOTAR videos in the world don't mean much if you don't have a grasp on these basic aspects first.

 

[MAHLMAN]

Also, and I'm not trying to be a dick at all, but all the gauges and SOTAR videos in the world don't mean much if you don't have a grasp on these basic aspects first.

That's why I am here asking questions. Got a good source to point me to for learning the basics?

 

[MAHLMAN]

Speaking of questions, and this gets back to what exactly is a good source for info, I have an aluminum barrel nut on the Palmetto. I read, for what it is worth, that steel can be better then aluminum in this application. Yes or no and why?

 

[TonyTheTiger]

That's why I am here asking questions. Got a good source to point me to for learning the basics?

Honestly I don't. Everything I know is just from years of working on guns as a hobbyist, I've really never looked for a good source of info on this stuff. I'm sure one exists and someone will mention it here.
The SOTAR stuff is cool, and technically very correct, but most of it is so far over the head of 99% of AR assemblers that it's just as likely to cause them trouble as it is to help them.

 

[TonyTheTiger]

Speaking of questions, and this gets back to what exactly is a good source for info, I have an aluminum barrel nut on the Palmetto. I read, for what it is worth, that steel can be better then aluminum in this application. Yes or no and why?

That'll be the subject of some debate now and then. In theory the steel nut will be more rigid and a better HG mounting material. And aluminum will be a better thermal match to the aluminum upper it's screwed onto when things heat up.
I'm not sure I've ever seen any definitive testing to prove one better than the other, and well respected brands have successfully used both in their guns with no real problems that I've ever heard of.

 

[johnnyvw]

Keep in mind that maximum gauges for 223 and 556 are different...max headspace for 556 is 4.736 (this is according to the Forster information). So using the 223 no-go and field gauges may still show excessive headspace

 

[MAHLMAN]

Honestly I don't. Everything I know is just from years of working on guns as a hobbyist, I've really never looked for a good source of info on this stuff. I'm sure one exists and someone will mention it here.
The SOTAR stuff is cool, and technically very correct, but most of it is so far over the head of 99% of AR assemblers that it's just as likely to cause them trouble as it is to help them.

Well the beginning of that is where I am at. Years ago I bought a Haas VF3 and had no idea how to run it. People thought I was nuts. You open your wallet and pour the money out you will learn. I had no idea how much learning grief I was going to be in as the mill led to having to learn Solid Edge so I could make 3d parts in cyber space to feed to the mill after I learned the CAM programming.

I can quickly sift online information in areas I know about. There are so many dubious things said in firearms though and I don't have the knowledge to reliably filter the trash out yet. Today I learn that all those gauges touted by people like Brownells just might not be necessary.

 

[msgriff]

Also headspace should be checked with bolt completely disassembled.

I somewhat agree, but for different reasons, like looking for machining debris at the bottom of the ejector(s) channel. If the gauge doesn't have an extractor groove or similar, the extractor should be removed. Someone else had a conversation with Dave Manson at Manson Precision Reamers relating to this, here is an excerpt from that conversation:

1. The cutout on the back of his gages will not provide clearance for the ejector and was never intended to. It is there to drive the gage during manufacture when grinding between centers.

2. The ejector and extractor do not have to be removed when checking head space on an AR and will not affect the results. The tension on the extractor will have to be overcome but after that the bolt will either close or it won't.

Image of a Manson gauge:

 

[strikeeagle1]

Brownells has the 5.56 NATO max headspace gauge dimensioned to Colt specifications.

 

[MAHLMAN]

I somewhat agree, but for different reasons, like looking for machining debris at the bottom of the ejector(s) channel. If the gauge doesn't have an extractor groove or similar, the extractor should be removed. Someone else had a conversation with Dave Manson at Manson Precision Reamers relating to this, here is an excerpt from that conversation:

OK if you do that do you also check for magnetism which could theoretically collect steel shavings from where ever?

 

[strikeeagle1]

OK if you do that do you also check for magnetism which could theoretically collect steel shavings from where ever?

Doesn't everyone. However unless the washer is painted orange it is not mil-spec and will not work.

 

[357Max]

OK if you do that do you also check for magnetism which could theoretically collect steel shavings from where ever?

I check on initial build.

Doesn't everyone. However unless the washer is painted orange it is not mil-spec and will not work.

I actually took his Master class a few years ago. It was a good time & a long f'ing day.

As for the barrel nut question. There will be a lot of different opinions on that subject.
Sure an aluminum barrel nut will work fine. I have one in Geissele rail. That said I prefer Titanium or steel. My rational for that is that the barrel nut is basically the biggest heat sink area on an AR. Aluminum's thermal expansion rate is roughly double that of titanium or steel. So with an aluminum barrel nut at basically the hottest location there is a lot of growth/shrinkage at a torqued connection. Even though both the receiver and aluminum nut should in theory grow/shrink together, what effect does that have on the torque value long term? The other issue (in my mind) is that the nut grows/shrinks in diameter inside the handguard & the handguard screws are steel. The steel retaining screws stretch and torque loss is the result.

The above is just rational/theory bla bla.

In practice the only handguard I've had to fight walking forward from the receiver has been a Geissele MK4 with the aluminum barrel nut. That also happens to be the only AR I currently have built with an aluminum nut.

I'm about to build an Aero enhanced with a Sgt of arms rail, but that design has the steel hand guard screws fastened into the receiver, not acrossed it.

 

[MontanaMan]

I do have the Forster 1.4636 223 go NATO minimum and the 1.4666 Forster 223 no go set. Somewhere around here I also have that 1.4646 one SOTAR recommended

It's always best & easiest & (IMO) most reliable, to check the uninstalled barrel by hand with a stripped bolt; but it can be done assembled, with the bolt stripped (preferred) or not, but that's not the best way unless you have special HS gauges as already discussed.

I check every barrel I get before I use it & in the 25-30 that I've used, I've only had a problem with one, & it was short, not long, & would not accept any of half dozen different new bolts nor a Go-gauge. And that was a Wilson Combat barrel (hint), if your upper is a Wilson Combat & not a Wilson Arms upper.

If your No-Go gauge is really 1.4666, a good barrel is gonna accept that as it's well below normal max headspace for a 5.56 or even a 223.................there is normally about .005" - .007" between Go & No Go, & as pointed out by others, the military allows .010" more than the Go gauge dimension for the No-Go on a 5.56.

I have a bolt drawing & FYI, & for what it's worth, I've never seen a bolt out of spec.

MM

 

[MAHLMAN]

Well I learned two things on this thread. These NATO barrels are in spec with NATO go and no go gauges. Hat tip to the gentleman who told me to turn down the bolt end of the gauge to allow for testing bolt to barrel fit and not have to take anything apart to do it. BCG would not close on this gauge.