Reading SAAMI spec sheets

[NZ_Fclass]

Sorry but it is a negative tolerance. the dimension is 2.204" maximum to 2.187" minimum. SAAMI Cartridge Dimensions are Maximum, so no positive tolerances, except one that is the grove in front of the ri

Sorry but it is a negative tolerance. the dimension is 2.204" maximum to 2.187" minimum. SAAMI Cartridge Dimensions are Maximum, so no positive tolerances, except one that is the grove in front of the rim..

Thanks

 

[precision.riflecraft]

To be technically correct the dimension shown is not headspace. Heasspace is defined in the minimum Chamber drawing. The dimension in question is simply the dimension of the cartridge to allow the maximum cartridge to mate with the minimum headspace chamber.

Is it not true that the term "headspace" is also used in terms of cartridge measurement, hence "Hornady Headspace Comparator"? That tool measures the brass, not the chamber.

 

[precision.riflecraft]

There is no guarantee that any comparitor will hit the shoulder exactly on the datum shown in the drawing. They are used for making comparisons, hence the name. If on the other hand you have a GO gauge then you can make comparisons to it.

Good point, thanks!

 

[precision.riflecraft]

Edd made a VERY important point. The first print is of the cartridge. All of the dimensions are designed so it will fit in a chamber. The print for the chamber has completly different numbers. A GO headspace gage will be of the minimum chamber dimension.

I should have also included the second half of the drawing, illustrating the chamber.

 

[precision.riflecraft]

It is easy to give advice to spend other people's money..... but if you are going to stick with this game and dedicate to good calibers, that advice from @BoydAllen to get yourself a chamber Go Gage is going to come in handy as you cycle more examples of chambers/bbls over the years.

Having a reference standard to set up your comparators can be very handy.

With just one gun, your idea still works fine and is an important concept to grasp early. How brass behaves with cycles is important. If you were to zero on your virgin Lapua, then check after several cycles of neck-only until closing the bolt indicated the brass was getting tight, you would see the behavior.

Just be sure to maintain that virgin setting if you don't have the Go Gage, in case the tool is disrupted in the time it takes to cycle the brass.

Also learn to take micrometer readings to the nearest 0.000X" on the 0.200 line and the shoulder as best you can and keep good notes. There is some taper in most cartridge designs there, so play with these concepts for a while since it makes the micrometer anvil contact important. Good Luck.

Good advice - thanks!

 

[6bra1k]

Is it not true that the term "headspace" is also used in terms of cartridge measurement, hence "Hornady Headspace Comparator"? That tool measures the brass, not the chamber.

lots of people make mistakes...it does not make what they say "correct" SAMMI has a def of headspace

 

[precision.riflecraft]

lots of people make mistakes...it does not make what they say "correct" SAMMI has a def of headspace

I looked it up and you're right - SAAMI's definition of headspace clearly concerns the chamber, not the casing.

However, for the sake of conversation, I just learned another way of thinking about headspace from an article on Redding's website that makes a lot of sense. They use that term quite literally - as the space between the case head and bolt face - writing "headspace is simply the distance between the head of the cartridge case... and the... face of the firearm's bolt": https://www.redding-reloading.com/tech-line-a-tips-faqs/145-dealing-with-headspace

A wise man once admonished me to "try not to be a slave to language". Words are just symbols, and their symbolism evolves over time. If I wrote this sentence in 16th century English, no one here would understand it.

 

[Doom]

Is it not true that the term "headspace" is also used in terms of cartridge measurement, hence "Hornady Headspace Comparator"? That tool measures the brass, not the chamber.

It is used but incorrectly. Yes I know I am being picky to an extent but since we often refer to SAAMI and throw the term around it can and does lead to confusion. Headspace in in relation to case and chamber is only one dimension and it refers to the Chamber dimension.

 

[precision.riflecraft]

It is used but incorrectly. Yes I know I am being picky to an extent but since we often refer to SAAMI and throw the term around it can and does lead to confusion. Headspace in in relation to case and chamber is only one dimension and it refers to the Chamber dimension.

Cheers, it almost seems we need another word for the case base to datum line dimension.

 

[Edd]

I looked it up and you're right - SAAMI's definition of headspace clearly concerns the chamber, not the casing.

However, for the sake of conversation, I just learned another way of thinking about headspace from an article on Redding's website that makes a lot of sense. They use that term quite literally - as the space between the case head and bolt face - writing "headspace is simply the distance between the head of the cartridge case... and the... face of the firearm's bolt": https://www.redding-reloading.com/tech-line-a-tips-faqs/145-dealing-with-headspace

A wise man once admonished me to "try not to be a slave to language". Words are just symbols, and their symbolism evolves over time. If I wrote this sentence in 16th century English, no one here would understand it.

If they did that, they incorrectly defined headspace. The distance between the cartridge base and the bolt face is..

HEAD CLEARANCE​

The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace.

Glossary - SAAMI

saami.org

 

[precision.riflecraft]

If they did that, they incorrectly defined headspace. The distance between the cartridge base and the bolt face is..

HEAD CLEARANCE​

The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace.

Glossary - SAAMI

saami.org

Interesting! I learn something new every day here.

 

[Doom]

In 43 years as a practicing Engineer I have been bitten more than once by the misuse/misunderstanding of terms. The more humorous ones were heated debates that turned out that both sides were arguing the same point. The more costly/dangerous ones were where two parties agree on something but their definitions are different.

 

[Edd]

There is one frequently used cartridge term that I find amusing even though I think it is being used correctly. I try not to use it. That word is “head”. In my human world, it doesn’t seem like the neck and the head should be on opposite ends of the body.

 

[precision.riflecraft]

In 43 years as a practicing Engineer I have been bitten more than once by the misuse/misunderstanding of terms. The more humorous ones were heated debates that turned out that both sides were arguing the same point. The more costly/dangerous ones were where two parties agree on something but their definitions are different.

The Hubble debacle comes to mind. Perhaps in hindsight it should be renamed The Humble.

 

[precision.riflecraft]

There is one frequently used cartridge term that I find amusing even though I think it is being used correctly. I try not to use it. That word is “head”. In my human world, it doesn’t seem like the neck and the head should be on opposite ends of the body.

Good point - I never thought of that.

 

[Vinootz]

I know this thread is old but maybe someone can explain the shoulder angle numbers next to degrees? Some have another number next to the degrees number with a foot symbol. For instance: 30-06 shows 17 degrees- 30’.
8mm Mauser shows 20 degrees- 48’. Thanks.

 

[358WCF]

I know this thread is old but maybe someone can explain the shoulder angle numbers next to degrees? Some have another number next to the degrees number with a foot symbol. For instance: 30-06 shows 17 degrees- 30’.
8mm Mauser shows 20 degrees- 48’. Thanks.

Seventeen degrees, 30 minutes... or 17 1/2 degrees.

It's a smaller measurement than degrees... 60 minutes per degree.