how to use headspace gauges?

[Robb_Jensen]

@turnero

I use the Forster gauges and have declared a few rifles as “unsafe to fire” because it closed on the field gauge.

Now my questions is, Is it still possible that those rifles will not close when using a USGI FIELD? There by making it still safe to fire?

Yes, some may close on a .223 Rem FIELD but not a USGI FIELD.

USGI FIELD is 1.4730"
.223 Rem FIELD is 1.4700"

As mentioned USGI 5.56mm FIELD is more forgiving.

Just for shits and giggles a M249 SAW 5.56mm FIELD is 1.50216" which is why I have repeating have said not to reload or shoot reloads that are from military brass that has gone through a M249 SAW or any belt fed machinegun.

[Iraqgunz]

gotm4,

Spot on. What’s really funny is we ordered some M249 “armorer kits” and I almost blew a headgasket when they sent me Forster Go/ No Gauges. I contacted the vendor and had to explain that the are differences in the dimensions and the gauges which is why they have (2) different NSN’s in the TM. They acted like I was speaking Martian. Unfortunately, once items like this get here getting them out is a bitch.

@gotm4

Yes, some may close on a .223 Rem FIELD but not a USGI FIELD.

USGI FIELD is 1.4730"
.223 Rem FIELD is 1.4700"

As mentioned USGI 5.56mm FIELD is more forgiving.

Just for shits and giggles a M249 SAW 5.56mm FIELD is 1.50216" which is why I have repeating have said not to reload or shoot reloads that are from military brass that has gone through a M249 SAW or any belt fed machinegun.

[C4IGrant]

@Paul Cataldo

I gotcha. You see where I’m going with this?
Basically, what I’m trying to determine, is IF I am buying uppers, lowers, and bcg’s from various sources, then do I need to be checking HS on all my builds??
OR, do I just need to go shooting, and call it good if the weapon performs reliably.???
Thanks.

It is NEVER a bad idea to check HS on anything (especially when putting a new bolt with an old barrel).

The purpose of “fitting” a bolt to a barrel is to improve accuracy.

C4

[turnero]

@gotm4

Yes, some may close on a .223 Rem FIELD but not a USGI FIELD.

USGI FIELD is 1.4730"
.223 Rem FIELD is 1.4700"

As mentioned USGI 5.56mm FIELD is more forgiving.

Just for shits and giggles a M249 SAW 5.56mm FIELD is 1.50216" which is why I have repeating have said not to reload or shoot reloads that are from military brass that has gone through a M249 SAW or any belt fed machinegun.

Thanks so much. I’ll have to order a USGI FIELD gauge and hope that I can still revert some of those rifles into “safe to fire” conditons.

[Iraqgunz]

Please let me know when you find them. I’ll buy everyone they have. I have never seen Milspec gauges outside of the supply line.

@turnero

Thanks so much. I’ll have to order a USGI FIELD gauge and hope that I can still revert some of those rifles into “safe to fire” conditons.

[gjj]

Where is a good place to buy a USGI field guage for the 5.56 AR15?

[turnero]

@Iraqgunz

Please let me know when you find them. I’ll buy everyone they have. I have never seen Milspec gauges outside of the supply line.

I might just have to make one (or 2 ) for myself. Have access to a CMM and a precision grinder. I think I’ll duplicate the “go”, “no go” and “field” gauges then make one more to the dimension of 1.473"

[armakraut]

http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=6646&title=5.56mm%20(.223)%20HEADSPACE%20GAUGE

Is this gauge any good?

[Spooky130]

@C4IGrant

It is NEVER a bad idea to check HS on anything (especially when putting a new bolt with an old barrel).

The purpose of “fitting” a bolt to a barrel is to improve accuracy.

C4

How exactly is a bolt “fitted” to a barrel?

Spooky

[Iraqgunz]

BTW,

My least favorite company Bushamster is actually selling G.I Spec “field” headspace gauges made by Clymers. I think they are 30.00.

[turnero]

@Spooky130

How exactly is a bolt “fitted” to a barrel?

Spooky

I dont know if this procedure is the right way to do it but we have done it more than a few times.

remove barrel extension and remove .001" of metal from the step where the barrel extension rest and also from the where the bolt lug are to touch thereby moving the barrel extension forward by .001" yet maintaining the void for the bolt lugs to fit in.

if you still dont get the right fit, repeat the procedure again.

I have not yet made the 5.56 mm field guage cause I figured that if we will be fitting bolts this way then I’ll just have to use the .223 field guage and get a better fit.

[drck1000]

Apologies for resurrecting a 3 year old thread, but I figured better this than start a new one.

Anyways, I recently purchased a Clymer’s Field Headspace 5.56/.223Gauge from Bushmaster and was researching the proper use (thanks for the lead on that Iraqgunz). There appears to be come conflicting information, so I have two questions to try to clarify:

1. Do you need to remove the ejector for proper headspace?
2. What else needs to be removed from the bolt or BCG?

I read through this thread and the following thread:

https://www.m4carbine.net/showthread.php?t=87829

I also read through the instructions:

http://www.brownells.com/userdocs/learn/Inst-300%20Colt%20HS%20Gauge.pdf

I just want to be clear on the proper use as I got a bit confused on the proper use of the Clymer/civilian version of the Field Headspace Gauge.

The directions indicate that you need to remove both the extractor and ejector. However, in the linked thread, it appears that the ejector may not need to be removed, assuming that it is working properly and the spring allows it to retract in it’s normal operation. It is my understanding that removal of the ejector is also somewhat of a PITA, so if it’s not necessary, that’s good.

In this thread, Grant mentions to “not re-install the firing pin or cam pin” and that the extractor stays in, but the spring and insert is removed. However, Iraggunz indicates that the TM instructions are to put the bolt in complete. I understand that the TM instructions are for the USGI field gauge without the case rim.

Regarding the installation of the cam pin back into the BCG/bolt, is that irrelevant since the bolt would bottom out in the bcg when all the way forward? Forgive my ignorance on the positioning of the bolt in the BCG when the bolt is in battery. I just assumed that the cam pin slot provided the stop for the bolt.

I bought the field headspace gauge as I will be swapping out a complete BCG on a couple of my guns (semi-auto to full-auto, and different brand) and also just to have to be able to occasionally check headspace (just to be sure).

Thanks!

@C4IGrant

Barrel can stay in the receiver. Generally on Go/No Go gauges, you just need to remove the Extractor spring and insert and then put the bolt back into the bolt carrier (do not re-install the firing pin or cam pin).
Slide the BCG back into the receiver. The end of the bolt carrier should poke out the back of the receiver slightly. If it sits flush with the receiver, then you have a problem.

C4

@Iraqgunz

I’ll run it down the way it is in the TM and how it is done in the military.

Insert charging handle, bolt assy. (that means complete), and bolt carrier into upper receiver.

Insert headspace gage into chamber area.

Press the rear of the bolt and carrier assy. and charging handle forward using light finger pressure into the chamber area.

Bolt should not rotate into the locked position and the bolt carrier must protrude from the rear of the upper receiver assy. for proper headspace.

[5pins]

The cam pin and firing pin must be installed or the bolt will not turn to lock in the barrel extension. With the civilian version the extractor and ejector should be removed but it can be done by just removing the extractor. The ejector will compress and add more resistance but it will still work.

[drck1000]

@5pins

The cam pin and firing pin must be installed or the bolt will not turn to lock in the barrel extension. With the civilian version the extractor and ejector should be removed but it can be done by just removing the extractor. The ejector will compress and add more resistance but it will still work.

Ok. Thanks!

When you use the headspace gauges with the case rim, do you remove the extractor completely? Or do you only remove the extractor spring and that little post?

[Iraqgunz]

You simply remove the extractor pin and extractor and then insert the gage into the chamber and push the bolt forward.

@drck1000

Ok. Thanks!

When you use the headspace gauges with the case rim, do you remove the extractor completely? Or do you only remove the extractor spring and that little post?

[drck1000]

Very good! Thanks IG!

@Iraqgunz

You simply remove the extractor pin and extractor and then insert the gage into the chamber and push the bolt forward.