Headspace comparator question

[Louie12]

Hello everyone,
I wanted to get some feedback on the SAC haedspace comparators. I been reloading for about 1yr and still learning.. Love the hobby but man some days just can't make things work.

I been using the Hornady headspace kit and it's worked for me. it take some time learning how to use them since there is a lot of play on the brass. For Christmas got some money so I went out and bought SAC comparator. For now I wanted to start out with the 223 and 308 WIN brass.

I received the kit a couple days ago and to my surprise I'm more confuse now on my measurements. I was wondering if someone might be able to help me understand something or I'm missing something.

I have fired brass from my Remington 700... Remington core-lokt ammo. All brass I have removed the primer and no brass has been resize yet.

Hornady Measurement using the D400 - 1.6230 to 1.6235
SAC headspace bushing 30 cal x 20 - 1.5335
a difference of 0.0895.

What gives dont understand why it's so off. I thought it would sorta match with the Hornady measurement. When I purchase the SAC kit I reach out to support to make sure I had the right kit.

Any feedback would be awesome... thank you,

 

[simonp]

Different tools will give you different results. The SAC is designed to be more precise, if you believe their marketing, but whether or not it is is moot. You need to pick a tool and stick with it and those numbers so that everything is consistent.

The numbers themselves to some extent are immaterial because different people will handle the tool differently and get different numbers, if you hand the SAC comparator to 4 buddies with the same brass you are likely to get different numbers depending on how hard they handle the tool.

 

[Doom]

The Hornady is measuring approx 0.400" diameter (single point)on the shoulder and is not dependent on actual shoulder angle. The SAC mimics the 20 degree shoulder and the maximum case diameters at the 1.5598" and 1.7116" lengths (or possibly the minimum chamber dimensions). Where it actually hits will depend on the actual chamber it's fired in. These are comparators and should not be compared to any other meaning tool other than the specific one used.

 

[bahadunn]

Hello everyone,
I wanted to get some feedback on the SAC haedspace comparators. I been reloading for about 1yr and still learning.. Love the hobby but man some days just can't make things work.

I been using the Hornady headspace kit and it's worked for me. it take some time learning how to use them since there is a lot of play on the brass. For Christmas got some money so I went out and bought SAC comparator. For now I wanted to start out with the 223 and 308 WIN brass.

I received the kit a couple days ago and to my surprise I'm more confuse now on my measurements. I was wondering if someone might be able to help me understand something or I'm missing something.

I have fired brass from my Remington 700... Remington core-lokt ammo. All brass I have removed the primer and no brass has been resize yet.

Hornady Measurement using the D400 - 1.6230 to 1.6235
SAC headspace bushing 30 cal x 20 - 1.5335
a difference of 0.0895.

What gives dont understand why it's so off. I thought it would sorta match with the Hornady measurement. When I purchase the SAC kit I reach out to support to make sure I had the right kit.

Any feedback would be awesome... thank you,

Comparators give you a relative measurement. They aren't made to be precise like gauges are. So say you want to bump the shoulders back 0.002. You'd 0 your the pre full length sized brass in your calipers using the comparator and then you'd size your brass and use the comparator to verify how much shoulder bump you got. Most comparators will be off. Take a 308 go gauge for example with a known length of 1.630. My comparator will measure it as 1.624 (0.006 short). It's not a guage though and it's not meant for exactly measurements like that. It's meant for comparing one measurement to another. How much did the shoulder move, etc... Also for this reason different comparator brand will take different readings if used as a guage (which they are not a gauge). If you want a guage you get a headspace gauge.
At least that's my understanding. Anyone can correct me if I'm wrong.

 

[FLIGHT762]

Another example of two comparators, a Hornady .400 and a Sinclair that measures off of the shoulder angle.

On a 1.630" 308 Winchester go gauge, The Hornady measures 1.611" and the Sinclair measures 1.561".

They are both accurate measurements on that 1.630" Go Gauge.

This is why these tools are called Comparators.

 

[Rio Precision Gunworks]

Just to add on what everyone else has stated......

Be aware there are two types of tools for this kind of thing. There are comparators and there are datum gauges.

A comparator can measure from pretty much anywhere on the shoulder. The SAC specifically has inserts that match the angle of the shoulder you are measuring. The hornady sits higher. Those are examples of comparators. They are only good when comparing measurements from the exact same set/device/tool. Not for comparing against other brands, or even other tools of the same manufacturer (you may get the same measurements from same company, but that's not guaranteed).

A datum gauge is a measurement tool. It has a hole cut to a specific predetermined size from a print. For example, a SAAMI 6gt print specifies a .375b datum gauge. Which in and of itself, the gauge has a spect that it should be cut to. That can now be used to compare measurements to any other measurement using the same datum gauge. So, if you wanted to share you base to shoulder datum measurement to someone 5 states away, they would need a datum gauge cut to the same spec.

 

[bahadunn]

Another example of two comparators, a Hornady .400 and a Sinclair that measures off of the shoulder angle.

On a 1.630" 308 Winchester go gauge, The Hornady measures 1.611" and the Sinclair measures 1.561".

They are both accurate measurements on that 1.630" Go Gauge.

This is why these tools are called Comparators.

Your .400 comparator is off more then mine. Mine is 0.006 short while yours is 0.019. I have the Hornady .400 also. To the Original Poster: This further illustrates what we are saying. Same brand but mine is off 0.006 while another person with the same comparator is off 0.019. Both will measure comparisons accurately when comparing how much shoulder bump or whatever. But when measuring the actual headspace of the case these aren't really the tools for that (headspace gauges are). The best we can do with our comparators if we have go/no-go gauges (which should be an exact length) is measure the go/no-go gauge and find out how off our comparators are. Then we can measure the case and add or subtract the difference to approximate the headspace. Not as accurately as a headspace guage but probably close to some degree. However, I'm not suggesting comparators be used for that purpose.

 

[FLIGHT762]

Yes, that .400 Hornady insert is off by .019". It is a very old one I bought many years ago. I believe it was a Stoney Point, before Hornady bought out Stoney Point. I do have another .400 insert I bought about about five years ago that measures 1.622" off of a 1.630 Go Gauge. It is .008" off.

These are made as Comparators, not Gauges.

 

[45-90]

Cartridge gauges are more of a reference tool..not an actual measurement.
I use the actual "go gauges" as a guide to show how far off, the reference chamber gauges are.
The same "go gauges" I used to chamber the barrel, as a guide and to show that the gauges are off...one plus .002" and the other minus .002".
Then set the brass case shoulder back, according to the actual chamber measurement.

You can use your finish reamer to make cartridge gauges, and sometimes it's necessary, with wildcats, and obsolete cartridges...and they will be more accurate.

 

[Herb Stoner]

They are not "off" - it is COMPARING case to case - hence the name. It is not measuring.

 

[45-90]

They are not "off" - it is COMPARING case to case - hence the name. It is not measuring.

They ARE "off", as shown... comparing is a reference, and not a qualified measurement, this is true.
But this way one can get an actual measurement, to "know", where you are at, with respect to brass case shoulder and rifle chamber shoulder, plus real variations and how much...the Hornady stuff is elementary junk, and a caliper, are approximately tools...basic simplistic tools for comparison only. And would not be qualified for measure on anything in a modern manufacturing facility. Just the facts.

 

[Louie12]

Thank you everyone for the feedback. To tell you the truth there is a lot of info on here I need to read about. This is all new to me and I'm glad to learn more from you guys. I went out the range this afternoon just so I could have some good current brass reading.

I measured 4 fired brass without the primer .
2 of them were 1.5425 and the other
2 were 1.5435

Sorry if this sound dumb but from my understand you have bump the brass 0.002 headspace. Meaning if I go with 1.5425 I should try to get the brass to 1.5405 correct...

 

[Rio Precision Gunworks]

Thank you everyone for the feedback. To tell you the truth there is a lot of info on here I need to read about. This is all new to me and I'm glad to learn more from you guys. I went out the range this afternoon just so I could have some good current brass reading.

I measured 4 fired brass without the primer .
2 of them were 1.5425 and the other
2 were 1.5435

Sorry if this sound dumb but from my understand you have bump the brass 0.002 headspace. Meaning if I go with 1.5425 I should try to get the brass to 1.5405 correct...

Just entirely forget the 4th decimal place with calipers. They aren't capable of being that precise.

You can easily move measurements .001 or more simply from more or less pressure with your thumb on the caliper.