What are your experiences using optimum barrel time (OBT)? If you're not familiar, it is a calculation based strictly on barrel length that provides several harmonic nodes for the bullet travel time through the barrel. Then you can use a program such as Quick Load to calculate the barrel time, which for a given bullet can be tuned based on powder type and amount (ie pressure and velocity). I found that this calculation agreed with ladder tests for my 308 and 6BR, it accurately predicted the flat spot for shot dispersion. For my new 223 I looked at a narrow range of powder near the OBT and while the vertical dispersion was not entirely flat it was narrow, and loads at the OBT give excellent groups. The Chris Long OBT is based on the calculation of a pressure wave that travels back and forth through the barrel, changing its diameter in the process; not exactly the same thing as the barrel "whipping". Going to the range this afternoon to try a few new loads using RL15 for the 308 to see if this short-cut process works out again. Share your results, or if you have ladder test data I will be happy to run them through Quick Load to see if it fits. An interesting approach that needs more validation.