February 6, 2023 – How to Make a Dummy round to Aid Barrel ChamberingHow to do it and why
A dummy round is a round that you create when you have a custom rifle built or a new barrel added to an existing rifle. This should include your preferred bullet types and brass, with the bullet placed at the optimal seating depth. A proper dummy rounds helps the gunsmith set your cartridge’s freebore accurately and ensures the correct chamber dimensions. Greg Tannel, a respected machinist, tool-maker and gunsmith, explains that the dummy rounds are used to measure the neck diameter, throat length, and diameter. This allows for [optimal] clearance between the loaded neck and where the bullet’s ogive touches the rifling. He recommends that the bullet’s full diameter be set just forward of the case’s neck-shoulder junction. Greg Tannel created a helpful video that shows how to make a dummy gun. Greg shows you how to measure and assemble the Dummy and how it will be used in the barrel chambering process. Greg points out that the dummy should contain NO primer and no powder. This video is highly recommended for rifle shooters. Even if you don’t need a new rifle anytime soon, you can still learn important information about chamber geometry, leade, freebore and chamber geometry. This video has received 782,000 views. These are actual YouTube comments: This is the best explanation that I have ever seen. Thank you sir. — P. Pablo Nice video. This is a great video. I wish that this was available when I first started reloading and custom rifle building. Your work is outstanding. Brandon K. Great job explaining chambering clearances. D. Giorgi Another cool tool — The Stub Gauge. After your gunsmith has chambered your barrel, you can have him create a Stub Gauge. a cast-off barrel section chambered like your actual barrel. The stub gauge allows you to measure the length to lands and freebore of your barrel when it was new. This will give you an accurate baseline to measure how much your throat has eroded over time. You will need to measure your barrel in order to accurately determine the length-to-lands dimension. However, your throat wears over time. The barrel stub gauge is used to determine the initial bullet seating depth. The seat depth is adjusted based on the observed throat erosion or your preferred seating depth.
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