Headspace Gauges (Go, No Go)

[SingleSeven]

Do I need to remove any of the bolt head components, i.e., ejector, extractor, or firing pin, when using the go and no go gauges to check headspace? If not, should the rim of the gauge be held captive by the bolt like the rim of a cartridge would be? My PTG go gauge does not catch by the rim at all and the no gauge only catches on one side? Just trying to figure out if the gauges are defective or if they are supposed to work this way. Sorry for the newbie question. Thanks.

 

[dfrosch]

Some people remove the ejector and spring. I don't.

The gauge rim should be captured by the extractor, just like a cartridge.

Can you measure the gauge rims and compare to a cartridge drawing?

 

[SingleSeven]

Thanks, that was an excellent suggestion.

I measured the go and no go gauge rims and they were both consistently 0.4605" in diameter.

I measured the rim diameter on a piece of spent brass and it was 0.4695."

From the SAAMI website drawing it shows 0.473" - 0.01" which I think means +/- so that would be 0.463" to 0.483."

Based on these measurements the gauges appear to be undersized for my rifle by a few thousands, which may explain why they aren't being retained by the extractor. It may also explain why the gauges were on clearance.

May I ask which brand of go / no go gauges you use?

 

[Bill Rodolph]

You should remove the ejector, spring and the firing pin assembly. You will have better feel with no spring tension of any kind. I have gauges that the extractor catches and some that it doesn't. The gauge is for measuring headspace, not whether the extractor works.

 

[SingleSeven]

That's good logic Bill. Is there any benefit in keeping the rim of the gauge captive against the bolt face when taking a measurement? Does that keep the gauge centered reducing the chances of canting errors? Or does this not matter as the gauge will self center as the bolt closes?

 

[Walt Krafft]

That dimension is +0 -.010. The gage will self center.

 

[dfrosch]

That's good logic Bill. Is there any benefit in keeping the rim of the gauge captive against the bolt face when taking a measurement? Does that keep the gauge centered reducing the chances of canting errors? Or does this not matter as the gauge will self center as the bolt closes?

The extractor would likely push the gauge slightly off center. But it'll center itself as the bolt closes.

You need the extractor to pull the gauge out of the chamber. The alternative is to punch the gauge out with a cleaning rod down the muzzle, which could damage the crown..

 

[243winxb]

I used a field gauge without removing anything on an M16. I think its different with the other gauges when chambering a new barrel or screwing on a new Savage barrel?

https://www.brownells.com/aspx/learn/learndetail.aspx?lid=12555

Do not remove the extractor on Remington rifles.
Place the gauge rim under the extractor, then place bolt into the gun.

 

[Bill Rodolph]

As stated above, the gauge will self center. Depending on the firearm, the extractor may have to be removed, your judgement call. I have had some combinations that the extractor wouldn't snap over the gauge and of course a claw extractor, the gauge must go under. Taking the extractor off of the bolt, leaves no doubt what you are feeling and no chance to break something. The gauge should fall out of the chamber with no need to be pushed or pulled. I have a small screwdriver with a magnet on the end that I sometimes fish them out with.

 

[SingleSeven]

Good discussion. I feel more confident now about the gauges. When I eventually replace the barrel on my Savage I'll remove all the bolt components before setting headspace, but initially I just wanted to verify that current headspace was correct, so I left the bolt parts intact. As such the bolt closed with the go and didn't close with the no go, so the gauges did their job even though they weren't retained by the extractor. I didn't need to use a muzzle rod or magnet to remove them (the no go was partially retained by the extractor) as they fell out on their own power with a little tipping of the muzzle.

 

[MGYSGT]

Lots of folks strip the bolt. I do not. Doesn't really seem to make a difference.

 

[dfrosch]

Good discussion. I feel more confident now about the gauges. When I eventually replace the barrel on my Savage I'll remove all the bolt components before setting headspace, but initially I just wanted to verify that current headspace was correct, so I left the bolt parts intact. As such the bolt closed with the go and didn't close with the no go, so the gauges did their job even though they weren't retained by the extractor. I didn't need to use a muzzle rod or magnet to remove them (the no go was partially retained by the extractor) as they fell out on their own power with a little tipping of the muzzle.

I was about to ask what action you were using. Here's some good info on the 110 series rifles: https://www.savageshooters.com/show...enterfire-FAQ-s-amp-Gunsmithing-Article-Links

When you disassemble the bolt head, do it inside a clear baggie. The ejector, extractor ball and their springs tend to fly if not contained.

 

[cem]

Under no circumstances - except looking for a lesson on why a little knowledge is a dangerous thing - close the bolt on a modern sporting rifle with the firing pin removed. Myself I do like to use a short firing pin in a MSR and remove the striker assembly in a bolt gun to avoid any potential for pushing the gage forward when I want to know what the headspace is. Cocking pieces do load the bolt. As when using a set of multiple gages by thousandths or so. Same depending on design for ejectors including how much of a nuisance.

In reply to the original question and for most modern firearms I'd say the answer is the ever famous it depends. "when using the go and no go gauges to check headspace?" when the question is does the rifle as assembled accept a SAAMI cartridge? and the next question is does the rifle as assembled have excessive headspace with a SAAMI cartridge? I see no gain from testing as modified to generalize to as not modified. YMMV

Many gages are made not to interact with the extractor. This avoids issues of must be fed from the magazine and extracts onto a concrete floor.

 

[Bill K]

Some do, some don't. Remember the headspacing measurement is from the shoulder to the case head fitting flush to the bolt and front of gauge touching the chamber shoulder, just lightly. So it will work either way.
Your preference.

 

[Straightshooter1]

Hmmm??? It seems the method depends on how the bolt and the headspace gauge is designed???

The first time I replaced the drop in barrel on my RPR I removed the firing pin assembly and the extractor per what has been described. I got the headspace set where it should be using my go and no-go gauges. After reassembling the bolt, I was curious as to what the difference is if I hadn't disassembled the bolt to set the headspace. I unscrewed the barrel out a little and reset the head space with the go and no-go gauges expecting there to be a .004 - .005 difference from before but found I got the same headspace. That was a couple years ago and recently I dropped in a new barrel in the same RPR and this time I didn't removed anything from the bolt and got the headspace I was after (afterwards confirmed by fired cases).

I've only changed barrel on an RPR. I wonder if I'm just luck in getting the headspace right (twice) or if there's something different where one method is necessary for a particular action vs. another???

 

[SingleSeven]

The PTG Gauges are recessed (relieved?) where the firing pin would protrude so no need to remove the pin assembly when taking a measurement. Not sure if other manufacturers do this too.