Who knows how to read SAAMI specifications?


#1

I have a little problem with SAAMI specifications.

Indeed I don’t understand how they specify a chamber and a ctge.

  1. The rule when specifing the dimensions of a mechanical part (ctge, chamber or anything else relative or not to a gun) is to always give the minima and the maxima dimensions, either directly or either by adding a tolerance to the minima (or the maxima) values.

  2. When something (a ctge for example) is designed to fit into another part (a chamber for example) it is obvious than the minimum dimension of this second part must be equal or bigger than the maximum dimension of the first part.

  3. Let’s take a look on this SAAMI drawing:

a) the rim diameter, base diameter (diameter under the rim), case length are well specified for the ctge and the chamber.
Minima and maxima are given.
But about the rim thickness we just have a reference dimension (0.075 for the ctge and 0.0736 for the chamber)
What does it mean ???(It is never written in the SAAMI book that a reference value is a minimum)

b) The ctge must enter the chamber.
But the rim thickness of the ctge (0.075) can be bigger than the rim’s depth of the chamber (0.0736) !!

Could somebody explain me that ???

thanks
jp


#2

The rim is .0624(max) -.016 (tolerance) = .0464 (min) thickness
The .075 dim is to the top of the Rim/Body radius, referenced above it. The rim/body radius is .015", while the matching chamber cut has a .020 to .025 radius at the same point.

Note that on the chamber drawing where it has a “Circled X” mark? That is the headspace dimention, and is specified (on this drawing) as being between .0624 Min and .0764 Max, so you have a “in spec” headspace clearance of .0000 (min chamber, max rim) to .0300 (max chamber, min rim)

The above is assuming that I haven’t forgotten how to read a drawing.


#3

JP,

Tailgunner seems to have remembered how to read a drawing! His explanation does well to describe the allowable fit conditions with the primary dimensions being those given as the headspacing points at .8900 dia. on the rim bevel.

Nice work, Tailgunner…

Dave


#4

hello Tailgunner and Dave,
Thanks to have answered.

But I disagree
What is called rim on a shotshell is the length where the diameter is bigger than the base diameter

Therefore the rim is the rounded seection plus the radius .
And it is related to what they call “reference” = 0.075

If the rim was 0.0464 (min) to 0.0624(max), it woud be too thin for a 10 gauge
And the CIP standard for such a gauge being 0.0590 (min) to 0.0748 (max), there would be a too big difference between the two standards.

I think we have to understand the SAAMI specification as :
Max of rim : 0.075 (what they call “reference”). It perfectly fits the max of CIP : 0.0748
(in this case the “pseudo rim” would be equal to 0.0624 (max) and the radius equal to 0.0124)

Min of rim : 0.075 (what they call “reference”) - 0.015 (radius max) = 0.060. It perfectly fits the min of CIP : 0.059
(in this case the “pseudo rim” would be equal to 0.060 which is within its specification: 0.0464 (min) to 0.0624(max) )

But what is the use of the min of the pseudo rim (0.0464) ???
It is not clear at all !

What do you think ???

Thanks
JP


#5

JP
Again I must refer you to the chamber drawing, and the dimensions with the “circled X” behind them. Those are the dimensions that define both the GO and NO-GO gauges
GO .8900 dia by .0624 thick
NO-GO .8900 dia by .0764 thick

By definition than (and as you stated in your original post), the thickest the cartridge rim can be (at the .8900 datum) is .624

For a cartridge manufacture, the dimension they will be most concerned with, and set their manufacturing equipment to not exceed) is the .0624 number. IOW if their equipment will normaly hold +/- .002 they may target a nominal dimension of .0619 (yielding a production spread of .0617 to .0621) but still keeping the “once in a blue moon” piece (the engineer types call it “3 sigma” error) that goes 2x nominal error to still function (.0615 to .0623) in a minimum spec chamber. Just because they are allowed to go as thin as …464 doesn’t mean that they will ever produce one that thin.

If you think the .030 min-max clearance is sloppy for a low pressure clambering, than you don’t want to look at the allowed clearances in a belted CF round with their high pressures


#6

hello tailgunner,

We will discuss later fabout the chamber and the fact the ctge must enter the chamber.

“By definition than (and as you stated in your original post), the thickest the cartridge rim can be (at the .8900 datum) is .624”

I never said that , I said : 0.075 looks to be the max value of the rim (taking into account the definition of a rim by SAAMI) :

The flanged portion of the head of a rimfire cartridge, certain types of centerfire rifle and revolver cartridges and shotshells. The flanged portion is usually larger in diameter than the cartridge or shotshell body diameter and provides a projecting lip for the firearm extractor to engage so that the cartridge or shotshell may be extracted from the chamber after firing.

You perhaps are not in the habit of 10 Guage.

therfore I will give you the saami secifications for a 12 gauge:

0.0576 -0.014 for the pseudo rim. It makes : 0.0436 mini to 0.0576 maxi
"reference value" 0.072
radius : 0.015 max

if we follow your reasoning it makes 0.0436 mini to 0.0576 maxi for the rim of a 12 Gauge.
Take a micrometer and any US 12 G shotshell and you will discover the rim is thicker than that.

The CIP gives : 0.610 mini and 0.728 max

If I follow my reasoning it gives :
Rim maxi = 0.072
Rim mini = 0.072 - 0.015 = 0.057
Which is close to the CIP measurements

make the measure and please tell me the result

JP


#7

JP,

Maybe a visual aid will be helpful in showing how the dimensions work out? If I get the chance I’ll generate a drawing showing a max. dimension cartridge in a min. dimension chamber for the 10 Ga. set you show.

Dave


#8

[quote=“jeanpierre”]hello tailgunner,

“By definition than (and as you stated in your original post), the thickest the cartridge rim can be (at the .8900 datum) is .624”

I never said that , I said : 0.075 looks to be the max value of the rim (taking into account the definition of a rim by SAAMI) :

JP[/quote]

[quote=“jeanpierre”]2) When something (a ctge for example) is designed to fit into another part (a chamber for example) it is obvious than the minimum dimension of this second part must be equal or bigger than the maximum dimension of the first part.
[/quote]

The rim must be equil to or thinner than the GO gauge

While DaveE creates another of his wonderful drawings, I’ll send a e-mail to a local chamber reamer maker to see if he would be willing to comment on the topic.


#9

[quote=“DaveE”]JP,

Maybe a visual aid will be helpful in showing how the dimensions work out? If I get the chance I’ll generate a drawing showing a max. dimension cartridge in a min. dimension chamber for the 10 Ga. set you show.

Dave[/quote]

ok, here is the 12 gauge

jp


#10

[quote=“jeanpierre”][quote=“DaveE”]JP,

Maybe a visual aid will be helpful in showing how the dimensions work out? If I get the chance I’ll generate a drawing showing a max. dimension cartridge in a min. dimension chamber for the 10 Ga. set you show.

Dave[/quote]

ok, here is the 12 gauge

jp[/quote]
and here the saamsa 1920 proofing the max rim is 0.072 (like CIP standard) and not 0.0576 max


JP


#11

JP,

Here are some boiled down basic drawings of the 10 ga. you started the thread with:

A couple things to note. The .0736 dimension for the chamber and the .0750 dimension for the shell are to imaginary intersecting points of the 55 deg. bevels and the case base and chamber wall lines. In reality there are radii there. A physical measurement of the rim thickness would require picking a point somewhere on the radius or bevel. SAMMI defined these points only as a reference for the purpose of conveying the needed information in the drawing. What is important is that at .8900" dia. and .0624" from the case head/bolt face, a point is determined to be the point of headspacing the cartridge. In the below view, it can be seen that with maximum cartridge dimensions and minimum chamber dimensions, a fit will still happen (with zero headspace gap).

I think this is a good example of a situation where the information being presented for specific purposes is not easily matched to real world measurable features.

Please pardon the lunchtime 2D drawings, but making cool looking models would take some time if the details were to be effective at showing the fit.

Dave


#12

I can certainly understand JP’s frustration in trying to figure this one out. I can imagine a reamer grinder or gunsmith pulling their hair over this, and they are the guys who the SAAMI drawings are suppose to be made for. Makes me wonder why SAAMI made a confusing situation even more so.

Ray


#13

Hello Ray, Dave and Tailgunner,

it is not frustration, but I just need to understand.

Here are shotshells and chambers shematics used by all the European manufacturers (French, Italian, German, Cheskolosakian, including British ones) and US manufacturers (prior to WWII) plus Russian, Chilean,and so on and a lot of others PLUS CIP members .
Please note the fact I say “PLUS” because you could think I am listing only CIP members when I give the details of the manufacturers. It is not the case because when I list the manufactuers it means I have their own datasheet and I am not refereing to the fact they belong (or not ) to CIP.


I showed you the SAAMI sheets for 12 gauge and 10 gauge

Don’t talk now about how the max ctge is fitting into the min chamber, but please let’s start by the beginning;

From the two SAAMI sheets could you please tell me what are the values of Tmax, Tmin for the chamber and tmax and tmin for the ctge, for 10 and 12 gauge.

No long sentence please because I don’understand english very well, but just the numbers:
Tmax =
Tmin =
tmx =
tmin =

Thank you very much
JP


#14

JP,

It really isn’t quite that simple, but I will try to generate numbers that you can use as reference.

Ray,

Bottom line is these drawings are not meant to designate specifically the “rim thickness” of the cartridge or the recess depth in the chamber to receive the rim. I think the intent is to provide min/max conditions for safe chamber and cartridge dimensions. The question of an accurate rim thickness measurement with calipers is a tough one as it comes down to just where you would measure it with the terminus at the case body having a radius that leads into a 55 deg. bevel.

While my drawing came out crappy in the file translation, I was trying to show the drawings do work to generate the geometry that is needed. Anyway, the thing being dimensioned doesn’t really exist and some ‘cyfrin’ is gonna have to be done in order to fabricate a reamer. For that purpose, I would be nice and add the center point dimensions of the radius.

Dave


#15

JP
My reamer guy is out of the office until Tuesday, but his office manager has stated that she’ll have him look at this thread when he gets back.
The angle and datum location are much more clear on the 12ga drawings


#16

JP,

Sorry for the delay.

Is this the dimension you wish to know for the rim thickness? If so, I’ll generate the min. and max. for the shells and the matching points for the chambers per the SAAMI drawings you provided.

Dave


#17

hello Dave
yes, this is what we call rim thickness.

How do you get 0.828 ? (it is just an example, or what you found?)
For 12 Gauge please

Thanks


#18

JP,

That is the 10 ga. max. dimension to that point. I’ll do the 12 ga. max./min. shell and chamber for you (as soon as I can get to it).

I wouldn’t think that’s an easy point to measure to!

Dave


#19

JP,

Here are the 12 Ga. dimensions you requested.

t min. = .0746"
t max. = .0798"
T min. = .0816"
T max. = .0842"

Please note that the minimum radius for the 12 Ga. shell is not defined and I used an arbitrary .005".

Here are the models and please pardon the different scale depicted. The .JPG export does not make equal output scaling by default…

Hope this is of help to you.

Dave


#20

Hello !
First at all, thanks to all of you who have tried to help me to decode these “funny” SAAMI specifications.

All the measurements you gave me haven’t satisfied me because they were too far away from :

  • the specimens I have measured
  • the CIP specifications

Therefore I decided to start from the beginning and to calculate all the parameters.

The first point to emphasize is the fact the 1992 SAAMI data are not written to check the ctges but to design a gauge to check the ctges

The second point is the fact they mixed on the same drawing the details about the checking gauge and the details about the rim itself (max radius allowed, aso)

The third point is the fact some of the data are redundant, meaning confusion and heavier drawing.

Let’s start now.

Application for the 12 Gauge ctge now

As you can see the values fit with CIP values

All this is for the 12 gauge ctge

If some people are interested I can show the same calculations for the 12 gauge chamber

Please correct the english sentences because I m sure there is a lot of mistakes

JP