Over the winter I took a look at substituting small rifle primers for large rifle primers in my .308. I limited the trial to velocities and standard deviations to make it a doable winter shop project. The purpose of the trial was to find which combination of primer size and flash hole diameter gave the most efficient and the most consistent use of the powder across a range of powders common in competition. Here’s the disclaimer. High velocity, low standard deviation does not guarantee accuracy. In addition, the sample is too small to draw a grand conclusion, however what I learned was enough to point me in the right direction when I do get out to the range.
For powders I used what was found in the CBA National equipment list for the .308 Win. Powder charges were worked up to come close to what the CBA results showed. In the end I wound up using 2400 @ 20.0g, 4227 @ 21.8g, RL10X @ 25.2g & 4895 @ 27.8g. Those charges put me in the 1650 to 1720fps ball park. The trial included small rifle brass with flash hole diameters of .059, .093 and .125” and large rifle brass with flash holes of .079, .125 and .140” large rifle primers. A single 10 shot string of each was shot.
But just to start the conversation I narrowed things down to what brass was commercially available. Off the shelf small rifle brass is available with .059 and .079 flash holes. Large rifle brass is only available with .079 flash holes as far as I know. As soon as a few medical things settle out I'll post the rest. Thanks, Bill C.
