My Chamber Length Measuring Tool

[JDinFbg]

I got to measuring the 30-30 cases I've fired multiple times in my Model 94 Winchester and noted many that were well over the SAAMI specified maximum. However, all of these over-length cases, after sizing, can easily be pushed into the chamber without any evidence that the case mouths are hitting the end of the neck cavity in the chamber. This peaked my curiosity as to how long the chamber in my rifle actually is. I suspect there are tools available (for a price) that can accurately measure this, but my curiosity did not rise to the level that justified spending any money. However, given that the 30-30 cartridge headspaces on the rim, I saw a fairly easy way to make a tool to measure this.

Using some old cases which were no longer suitable for reloading, I sized and decapped one, chucked it in my lathe, and drilled and tapped the primer pocket for 1/4"-20 thread. I turned the case around in the lathe and machined off the case just below the shoulder. I then took a 1/4"-20 x 2 1/2" machine screw I had, chucked it in the lathe, machined the end perfectly flat and square, and then screwed it into the case section I had made. With another sized case I seated a jacketed bullet without expanding the neck, then chucked it in the lathe and machined off the neck portion. I chucked the resulting neck portion in the lathe and machined it down until I had a cylinder with both ends perfectly flat and square.

Using these fabricated pieces, I dropped the cylinder into the chamber then pushed in the bottom half of the case with the threaded machine screw. Holding the rim against the chamber, I screwed in the machine screw until I felt resistance and knew that the cylinder portion had been pushed all the way forward in the chamber neck. I then removed the pieces, measured the length of both, and added the measurements to come up with the total length of my rifle's chamber. The results might be off by a few thousandths of an inch or so, but I determined that in my Model 94 Winchester the cases could be 0.052" longer than the SAAMI specified maximum before I'd have any chamber fit issues. There are obviously other reasons that come into play for trimming 30-30 cases to the proper length, but chamber fit is not one of them in my rifle.

 

[Blue68f100]

That's one way to do it. Even though the 30-30 head spaces off the rimed base. It's better for the brass to only set the shoulder back 0.001-0.002" for max brass life.

For finding the leads just split the neck so it holds the bullet lightly then chamber, remove and measure. This will tell you the max OAL for that bullet profile. Every mfg will have a slightly different ogive, changing the max OAL.

 

[243winxb]

Chamber Length- http://bulletin.accurateshooter.com/2018/03/how-to-craft-your-own-chamber-length-gauge/

Note that the bullet needs to expand the diameter.

 

[JDinFbg]

That's one way to do it. Even though the 30-30 head spaces off the rimed base. It's better for the brass to only set the shoulder back 0.001-0.002" for max brass life.

For finding the leads just split the neck so it holds the bullet lightly then chamber, remove and measure. This will tell you the max OAL for that bullet profile. Every mfg will have a slightly different ogive, changing the max OAL.

I was interested in finding the chamber length, not the OAL of the cartridge where the bullet hits the lands. For finding OAL with a given bullet, I just "bump" a fired case in the sizing die until the mouth of the neck gets closed down just enough to hold the bullet with a reasonable amount of sliding friction - enough that the bullet can be pushed into the case when the cartridge is chambered and enough that the cartridge with bullet intact can be extracted without the bullet moving or being left stuck in the rifling. I then chamber the cartridge and slowly extract it and can measure the OAL and base to ogive distance with a bullet comparator.

 

[JDinFbg]

Chamber Length- http://bulletin.accurateshooter.com/2018/03/how-to-craft-your-own-chamber-length-gauge/

Note that the bullet needs to expand the diameter.

That's a slick idea for rimless cartridges and where it's not easy to access the chamber.

 

[SGW Gunsmith]

I was interested in finding the chamber length, not the OAL of the cartridge where the bullet hits the lands. For finding OAL with a given bullet, I just "bump" a fired case in the sizing die until the mouth of the neck gets closed down just enough to hold the bullet with a reasonable amount of sliding friction - enough that the bullet can be pushed into the case when the cartridge is chambered and enough that the cartridge with bullet intact can be extracted without the bullet moving or being left stuck in the rifling. I then chamber the cartridge and slowly extract it and can measure the OAL and base to ogive distance with a bullet comparator.

I agree, and you made that very clear. I think Post #3 provided the best answer for your needs.