Christmas came early for me this year! The Ballistics By The Inch (BBTI) have done extensive testing to find out how much the revolver cylinder gap (the gap between the cylinder/chamber and the barrel of a revolver) affects performance. They shot and carefully measured over 7000 rounds.

The cylinder gap, and gas escaping from it, can be seen clearly in this photo.

From the BBTI website …

For many years people have wondered about the effect of the gap between the cylinder and the barrel (forcing cone) on a revolver. How much energy is lost due to this gap? Intuitively, a larger gap would probably mean a greater loss of energy (and hence bullet velocity), but how much functional difference is there? We decided to test it and see.

This is actually a more complex problem than it might seem at first. In addition to variation caused by the actual amount of space between the cylinder and the barrel (forcing cone), there are a number of factors which could have an effect on the loss of energy through the cylinder gap.

…

So, we decided to test a pretty wide range of different loads available in the caliber/cartridge of our test platform, an Uberti 1873 Cattleman Single Action Revolver (Colt Single Action Army clone) in .38/.357 magnum. In addition, the gun was modified to allow us to change the cylinder gap through the use of different shims on the barrel (where it screws into the frame) to create a cylinder gap of six thousandths of an inch (0.006″), one thousandth of an inch (0.001″), and “flush” (where the barrel was tightened against the face of the cylinder).

Because we expected the effect to be fairly subtle, we decided to do ten test shots of each ammunition brand/loading for each combination of barrel length and cylinder gap, measuring the velocity of the fired bullet over two chronographs set at 15′. This meant we fired thirty rounds of each ammo type at each 1″ of barrel length, altogether almost 7,000 rounds.

The BBTI team (after two years of “encouragement” from me) have also done barrel length tests of the .22 LR and .223 Remington. I will be referencing their site as I continue to preach the benefits of short barreled rifles 😉

Thanks BBTI 🙂