Factory Headspace Higher than SAAMI Maximum?

[Click_Here]

Messing around with the Hornady comparator and I wanted to measure my fired cases compared to factory loaded cartridges.
I measured a few cartridges of 6.5 CM Hornady 140gr ELD M and they were all 1.557
SAAMI Spec on headspace max is 1.551
Whats the deal with that?


My fired cases measure 1.560 bumping it back down -.002 would set me at 1.558 which is also above SAAMI spec.

Who is SAAMI and what does she do? Should I care about her or proceed with what my measurements are telling me?

 

[Varminterror]

Your tool does not allow you to measure actual headspace. The Hornady product ONLY allows you to establish a REFERENCE measurement, such as you have used to determine how to set your sizing die based on your fired case. This is described in the instructions included with your tool. Much ado about nuthin'.

 

[Walkalong]

Yep, you need headspace gauges or a trip to the gunsmith if you really want to know your rifle's actual mechanical headspace.

 

[Click_Here]

I wasnt trying to measure my chambers mechanical headspace. I was comparing SAAMI spec to a factory cartridge.
I get it though as Varminterror mentioned. Im using a reference tool not a precision gauge/tool.

 

[Varminterror]

I wasnt trying to measure my chambers mechanical headspace. I was comparing SAAMI spec to a factory cartridge.

View attachment 1187917

Again...

YOU DO NOT HAVE AN APPROPRIATE TOOL TO MEASURE HEADSPACE DIMENSIONS OF A CARTRIDGE. YOUR TOOL ****ONLY**** PROVIDES A REFERENCE MEASUREMENT. YOUR INSTRUCTIONS DESCRIBE THIS.

 

[Click_Here]

Again...

YOU DO NOT HAVE AN APPROPRIATE TOOL TO MEASURE HEADSPACE DIMENSIONS OF A CARTRIDGE. YOUR TOOL ****ONLY**** PROVIDES A REFERENCE MEASUREMENT. YOUR INSTRUCTIONS DESCRIBE THIS.

I know...you missed my edit by 10 seconds lol. Your Caps Lock is strong

 

[Howa 9700]

I have adopted the practice of buying a GO gauge for all the caliber's I'm loading for. I use the GO gauge to "calibrate" the case comparator. It establishes a known baseline to then measure where my chamber is relative to SAMMI specs. Of the three calibers I care about, one rifle is chambered to same depth as Go gauge.......one is 4 thousands over and one is 6 thousands over. They are what they are, and all get bumped back 1 to 2 thousands (just enough for a stripped bolt to close on sized brass without binding). But still nice to know where the chambers were cut, relative to SAMMI.

 

[Varminterror]

Im using a reference tool not a precision gauge/tool.

A reference tool can be precise tool, but the function and design of the tool is NOT to measure discrete values, but rather to PRODUCE a value from which meaningful values can be derived. If I have a ruler, I can't very well measure how long is a school bus, but if I have two busses of nearly the same length, I likely CAN well measure - precisely - that one bus is 6 5/16" longer than the other... THAT is what you can do with the Hornady headspace COMPARATORS.

 

[Varminterror]

I have adopted the practice of buying a GO gauge for all the caliber's I'm loading for.

That's a lot of money, and you're really early in your reloading journey - what's the real value of the expense there for you? That's a really convoluted dive into the weeds that I can't imagine can ever be truly fruitful for your process.

How exactly are you determining your chambers are 4 or 6 thou over, and what are they "over"? Over SAAMI Minimum headspace dimension, or over SAAMI Maximum dimension? How are you determining how far your cases are springing back after firing to know the chamber dimension vs. sprung-back fired case dimension? ALL of that work and ALL of that money spent to own gauges you don't really need... man, you can get the same knowledge you need with way less time and expense, and frankly, have BETTER info which isn't undermined by the variability of case springback...

 

[Soonerpesek]

Not sure…….
But I’m pretty confident that I, as well as MANY others here, could measure a bus with a ruler.
And be pretty precise with it….
What was the point in that statement…??

 

[Howa 9700]

Don't know if $40 for a Go Gauge is a lot of money (not to me as the gauge costs less than one box of factory ammo), but combined with new factory ammo, it helps me determine where my chambers were cut to relative to SAMMI min. Put another way......on a scale of 0 to 10......(almost literally 0 to 10 thousands) with zero being SAMMI minimum........I get to find out where my chamber resides on that scale. At least where the fired cases I recover balloon out to. I'm still only bumping them back 1 or 2 thousands, regardless. I could do that and do it blind and maybe it would not matter, but to satisfy my curious mind, I simply like to know where things stand.

But again, I'm going the extra distance to only bump the fired cases back 1 to 2 thousands to fit my chamber. If a guy were to follow the instructions on my die sets, the cases would get bumped back to about what factory ammo would be. In my situation, that would be 2 thousands for one gun to as much as 8 thousands for a different rifle. That is something I'd want to know. In short, it allows me to scratch an itch.

 

[Varminterror]

combined with new factory ammo

Why would you assume factory ammo is produced exactly to one end or the other of the 10 thousandths of SAAMI allowance for chamber headspace?

What if I told you - a LOT of folks have 4-5thou of clearance when they THINK they are only bumping 2thou? Springback really challenges our ability to use fired brass as a proxy for indirect measurement of our chambers.

$40 per gauge, go + no-go = $80 per set to do a proper job, I guess I’m glad I don’t have $1500 (or $3000) in gauges sitting around my shop just so I can calibrate a comparator bushing…

 

[Howa 9700]

My understanding of a GO gauge is it represents the minimum chamber spec for that caliber. When a smith or other sets up a chamber, the bolt has to be able to close on a GO gauge or chamber is too tight. So if I put the case comparator on one of those, and Zero the calipers, I've set the calipers to duplicate SAMMI minimum for that caliber. Also my understanding that factory ammo is made to chamber in SAMMI spec chamber, and to do that, they have to be sized to be equal to or less than SAMMI minimum.......and that then means equal to or less than GO gauge. And when I have measured the GO gauge, and then factory loaded ammo, I have found that to be true. Shoulder on those cases has been from 1 to 3 thousands less than the GO gauge. Insight. May not be for everyone, but I find it comforting to know what kind of chamber I'm working with.

So when fired, if the fired case I get back has expanded out some distance.........say 3 thousands over the GO gauge.......even if it went more, but due to spring back, it measured less than it really went, that doesn't matter much to me if it won't a stripped bolt won't chamber it. I"m still going to bump it back until the bolt drops on it without resistance. At least that what a lot of folks like Cortina are telling guys to do.

BTW, also find it comforting to know distance to the lands for any bullet I'm using. Pistol or rifle. Another glimpse into the depths of the chamber I'm working with. With pistols, some are content to just plunk it and if it fits, go with it. I like to take that one step further and find out the actual distance. If I'm close......or far, far away.

 

[MEHavey]

factory ammo is made to chamber in SAMMI spec chamber, and to do that, they have to be sized to be equal to or less than SAMMI minimum.......

^^^ THIS ^^^

 

[NMexJim]

Not sure…….
But I’m pretty confident that I, as well as MANY others here, could measure a bus with a ruler.
And be pretty precise with it….
What was the point in that statement…??

Define precise. When you’re dealing in a couple of thousands, a ruler is a hand grenade.

If you were able to buy a precise ”comparator” (note compare), you would be rolling in bucks. Production machining is not nearly precise enough for the kind of accuracy you’re talking about. That’s why the SAAMI standards allow a tolerance of -.007 in the cartridge and a min and max dimension in the chamber. It’s up to you to define the dimensions for you particular firearm.

 

[tmd16556]

I like the comparators. They’re really nice for sizing between chamber size and the maximum a die can size. It’s also useful to compare headspace on loads of the same caliber. How much bigger is one than the other, which rifle did this one come from, etc.
I agree that they could be used to measure headspace with a no go gauge, but the error compounds quickly with every step. If headspace gauges didn’t exist it would be better than nothing.

 

[Varminterror]

I find it comforting to know what kind of chamber I'm working with.

Introduce yourself to cerrosafe, far better opportunity for your “insight” than wasting money on gauges and chasing smoke by trying to calibrate on “well I know they say it’s supposed to be smaller”.

 

[JFrank]

Not to be snarky but

I wasnt trying to measure my chambers mechanical headspace. I was comparing SAAMI spec to a factory cartridge.
I get it though as Varminterror mentioned. Im using a reference tool not a precision gauge/tool.

View attachment 1187917

Does you comparator actually make contact at the .400 datum ?

 

[Click_Here]

Not to be snarky but


Does you comparator actually make contact at the .400 datum ?

It "looks" like it but I couldn't tell you if its actually at the .400 datum.

 

[JFrank]

It "looks" like it but I couldn't tell you if it’s actually at the .400 datum.

I think you need an inside mic to confirm.

I’ve never chambered a barrel personally but the guy running the lathe can make a big difference just running the reamer in an extra .001 or .002 or less. I just need to create enough headspace when sizing to chamber freely.

 

[Theinkman]

One of my prairie dog rifles is a Savage 110 .204 ruger. Bought new not too long ago and new brass has been hard to find. My father in law gave me a bunch (800+) cases that he had previously fired through his .204. Some once fired, some way more than once fired although there was no way to tell how many times. Because it was not fired in my rifle, I'm going to FL resize all. Question is how much shoulder bump do I want?

I measured a number of fired cases with a Hornady comparator and marked those cases with the measurement numbers I got. Then I took those cases and chambered them in my rifle. What I found was that cases that measured 1.554 and over on the comparator would chamber (bolt has a lot of force) but chambering those resulted in a very hard bolt lift. Cases measuring 1.553 and under chamber and resulted in an easy bolt lift.

Using a Redding S-type body die and their competition shell holders, I bumped the shoulders back on this brass to 1.551 and everything is fine. I don't care what SAAMI min/max numbers are; I want these cases to work in my rifle's chamber. A GO/No GO guage is useful to many but not to me. My chamber is telling me what works and the Hornady comparator is the tool I use to measure that.

 

[Walkalong]

Introduce yourself to cerrosafe, far better opportunity for your “insight”

Very useful stuff, helped me get the ID of my chamber's throat and the "wiggle room" on brass length in my Blackout.

 

[Walkalong]

I think you need an inside mic to confirm.

I’ve never chambered a barrel personally but the guy running the lathe can make a big difference just running the reamer in an extra .001 or .002 or less. I just need to create enough headspace when sizing to chamber freely.

Technically, when sizing to fit the chamber, that would be "Head Clearance". Where's Duffey when you need him.

 

[higgite]

Technically that would be "Head Clearance". Where's Duffey when you need him.

I think you mean Guffey. As frustrating as he was, I kinda miss him.

 

[Walkalong]

Ah yes, Guffey, that's it.