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Discussion Starter · #1 ·
Hi everyone! :)

Hope you're all doing fine.
Recently, I have been very confused when I started diving into some technical details on revolvers. I used to be a semi-auto guy but I'm starting to like revolvers a lot as well. So I'm familiar with how a non-rimmed auto-cartridge headspaces on the front of the chamber (=the datum reference) with it's neck. And of course we know that most revolver cartridges are rimmed and that they usually headspace on the rim.
However, when digging up some SAAMI specs, I found that there are cartridges that do not have a throat cut in the chamber of the revolver,while other cartridges have a throat cut. In particular, I'm talking about the 32. Short Colt (no throat according to SAAMI) and the .32 Smith and Wesson (throat cut according to SAAMI). I've attached the drawings of both.

So what have I not understood about throats in revolver cylinders? Is the difference in OD between the projectile and the OD of the brass the determining factor? So a cartridge where the projectile is almost as big as the brass does not require a throat to be cut and a cartridge, where the OD of the projectile is a lot smaller than the OD of the case does require a throat? :confused: I guess it is a very stupid question but I'm trying to understand this for days now...

Thanks a lot!
 

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Retired Moderator & Gunsmith
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So I'm familiar with how a non-rimmed auto-cartridge headspaces on the front of the chamber (=the datum reference) with it's neck.
This is true only for bottle neck rifle cartridges/chambers. Handgun cartridges and chambers work much different.

Both 32 cal cartridges in your examples do indeed have a rim, which is used to headspace the cartridge in the chamber. Cylinders for them do indeed have a throat. Let's make sure you are using the proper terms …. a cylinder throat is the section in front of the chamber that is bored to the same diameter as a bullet. It is usually about 1/2" long and feeds the bullet to the barrel's forcing cone. All revolver cylinders have throats.

The term "headspace" simply means …. what keeps the cartridge from seating too deep in the chamber and places the head of the case within a few thousandths of the breach face (pistol) or recoil shield (revolver)? With rimmed and semi-rimmed cases, obviously the rim does the job. With rimless cases, there is a "stop" inside each chamber that contacts the case mouth and prevents the case from seating too deep. This "stop" is visible if you look in a chamber and is only about .010" smaller in diameter than the case mouth but large enough where a bullet can pass through.

Some chambers can accommodate different cartridges such as the 32 Special and 32 Short. Why? When these cartridges are used in a revolver, their rimmed cases have to stop the case from seating too deep. Such is the case with 32 Fed Mag, which will also chamber a 32 H&R mag, a 32 Special, and a 32 Short. Chambers with a case mouth stop have to depend on the length of the brass case to achieve proper headspace so they only work for the specified cartridge. In most handguns, either type of headspace should be about .010", which is the measured distance between the case head and breach face (or recoil shield). Obviously if a brass case is shorter than SAAMI spec in a "headspace on the case mouth" chamber, headspace will increase by the same amount. As an example, a 45 ACP case is supposed to be .898" long with a headspace of .010". Most 45 ACP cases are shorter than SAAMI spec so if you have a case that is only .888" long, headspace will be .020". When headspace get's too generous, you risk poor accuracy and possibly light firing pin strikes.

You have to learn how to read SAAMI drawings because they use older engineering terms. For example, in your above SAAMI drawing for a 32 S&W (AKA 32 S&W Long), it shows a rim thickness of .054 - .010", which is engineereze for a max of .054" and a minimum of .044". The diameter of the rim is .375 - .012" or .375" max and .363" min. As you can see, the rim is larger than the body of the case (.339") by about .036". The 32 Short has similar measurements.
 

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Discussion Starter · #4 ·
Thank you very much for the in-depth reply and for your patience. Appreciate it! Now that you've explained it it makes perfect sense to me. I've also understood how the "054 - .010" is supposed to work. :)
As a gunsmith, can you actually recommend some good books to start learning and understanding how all of these fine details are working together?

Best regards!
 

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P08, After you get at least 10 posts, you can access the Forum E-Library where I have posted several documents. One is titled "Lead Bullets and Revolvers" that give some information and graphics that should help you understand how revolvers are supposed to work. Here's a link for future reference: https://rugerforum.net/e-library/19869-lead-bullets-revolvers.html

There are countless references on the Internet if you search for "gunsmith books".
 

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P08, After you get at least 10 posts, you can access the Forum E-Library where I have posted several documents. One is titled "Lead Bullets and Revolvers" that give some information and graphics that should help you understand how revolvers are supposed to work. Here's a link for future reference: https://rugerforum.net/e-library/19869-lead-bullets-revolvers.html

There are countless references on the Internet if you search for "gunsmith books".
Which I believe even Missouri Bullet Company references.
 
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