Can anyone point me to a source that would explain the different figures in any SAAMI Maximum Cartridge/Minimum Chamber drawing? I'd like to have a better understanding of the technical aspects of cartridges and chambers. Thanks

They are just dimensions, both at the maximum material conditions (MMC).  What do you have questions about?



The tolerance range is given so you can calculate the LMC (least material condition).

All of SAAMI's specifications can be found HERE

When reviewing measurements; the numbers that are not in parenthesis are in inches while the numbers in parenthesis are in millimeters as determined by the legend. When reading an actual dimension. Let's use the cartridge dimension below that is from the bolt-face to the .330" datum line as an example:

1.4666" - .0070"

Here is how to read this; for this part of the cartridge to be within specification it will measure from 1.4596" to 1.4666". How 1.4596" was determined is because this is .0070" ten-thousandths or .007" thousandths of an inch less than 1.4666". When a dimension has a minus sign after it, you subtract the amount after the minus sign from the dimension. If a dimension has a plus sign after it, you add the amount after the plus sign to the dimension.

This is how the tolerance range is determined for different areas of a cartridge or chamber; or the range of difference in length or diameter allowable for a particular area while still within specification.

Also, some blueprint drawings include a legend like the one above for 223 REM that lets you know the meaning of certain symbols (i.e., the X in a circle stands for headspace dimension).

Also, interesting to note that the maximum length case, 1.4666" is longer that the minimum length chamber, 1.4636" by .003"

And the minimum freebore diameter, .2240" is smaller that the maximum bullet diameter, .02245" by half a thousandths.

Thanks lysanderxiii and AR-4C, that helps.

A couple of questions. In the diagram above, there's a body length of "1.000 (25.40) B", but it's not the full length of the body. Where does that distance begin and end, and what does "B" for basic indicate? Then there are two lengths from the base of the case to the shoulder 1.4381 and and 1.4666. Why is the second longer dimension needed, which seems to end a little beyond the start of the shoulder?

You will notice that the 1.000" reference dimension is between two lines  The "B" stands for 'basic' a reference dimension.  It is there to define the case (or chamber) diameter at those planes.  The first plane is 0.200" from the base of the cartridge (or bolt face) and for the cartridge the diameter at this plane should be .3759", the second plane is 1.000" from the first plane, or 1.200" from the base of the cartridge, for the cartridge, this diameter should be .3584".

The 1.4381 dimension is to the theoretical circle made by intersection of the taper of the body and the taper of the shoulder which should have a diameter of .3542".  The 1.4666" dimension is to a datum circle on the shoulder cone that is exactly .3300" diameter, this is the 'headspace' dimension.

The reason for the use of a datum circle of .3300" is because there are tolerance in both the taper of the body and the taper of the shoulder which change the position of the theoretical location of their intersection, also you cannot measure to a theoretical point.

Thanks, that is very helpful.