by Hoot on Wed Jun 12, 2013 12:27 pm
Usually, the barrel nut that the handguard screws onto is perforated on the receiver end, so adding holes to the end cap at the other end should help provide a convective path. While you are correct that aluminum is an excellent thermal conductor as well as radiator, the layer of dead air between the inside of the handguard and the barrel acts like a thermal insulator. When you embed the thermocouple to test the temperature, make sure its glued or taped to the barrel 4-6" from the receiver and on the opposite side from the gas port so it doesn't pick up heat from the gas tube. Measuring the handguard surface temp won't tell you much about the barrel temp and measuring the barrel temp out beyond the handguard may not reflect the temperature beneath it. If you're waiting several minutes between shots or running a forced air cooling system between shots when the ambient temperature is high, then it may not matter.
Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.