I don’t reload for matches so I have never seen the need to own a case gauging tool to make sure my cases are within normal parameters.

I have a Remington Rolling Block that is chambered for the 7mm Mauser cartridge. It is a 1902 model exported to Mexico around 1910. It is super accurate and I reload full power cartridges for it. The first 100 rounds I loaded chambered perfectly. I used brand new cases that were full length sized. The next 100 rounds did the same. At this time I started neck sizing and I started using a different bullet both at the same time. This time about 75% of all the cartridges did not easily chamber and required some degree of force to chamber fully in order to fire. Upon my first investigation I found scuff marks on the bullet of a cartridge that was fully chambered and ejected without firing. My first look was for an obstruction in the chamber. Did not find anything. My next step was to have a friend watch the run out on the bullet of a loaded cartridge while I rolled it on the bench. He noticed some bullet run out.

I bought the RCBS Case Master in order to measure case neck run out, bullet run out, case neck wall thickness. It also measures case length and case head wall thickness. I checked case neck and bullet run out as well as case neck thickness and found every case within the maximum specs. Some were well within specs and some were close to being out without being out. I tried chambering empty cartridge cases and they all chambered easily. So I turned to a loaded cartridge and found one that would not chamber without force. I pushed it in as far as I could and extracted it and noticed the scuff marks on one side of the bullet. I checked run out on the cartridge and it was within specs. I then disassembled the cartridge and tried to chamber the case. And it turns out the case is the problem at the case head end. I full length sized the case and it now chambers correctly. So at least for now, it seems I will have to full length size every case every time.

I tried measuring the case head wall thickness and while it is thinner it is not enough to consider it out of spec. I still need to check out the scuff marks on the bullet. I think the cartridge was originally designed for a different shaped bullet since I am using a modern design hunting bullet. But I don’t think this was causing my chambering problem.

I really like this new tool and I think I will check out some of my other ammo and cases. Being able to measure the case head wall thickness will probably help me prevent a future problem. I added a few pics for you to see:

Might want to keep an eye out for this little tool to go with the case gauge.   

Might want to keep an eye out for this little tool to go with the case gauge.   

Wow! Didn’t know that existed. Thanks Old Mose!!! 

Nice write-up showing the practical application of the tool.  I was considering the Hornady version, but for about the same price the RCBS can provide more functions.  Thanks.

Nice write-up showing the practical application of the tool.  I was considering the Hornady version, but for about the same price the RCBS can provide more functions.  Thanks.

The RCBS is nice. I got the Hornady. What I like about the Hornadyis you can true up the cartridge quite easily and my experience has been it improves accuracy. The tools that are available these days are amazing,