I can tell you there will be out of an 11.5".  Not sure on a 16".

Flash is caused by continuing combustion of propelling powder particles entering an atmosphere rich in oxygen. Flash can be reduced through the use of low flash powder in ammunition manufacture or an external flash hider.

Suppressors are moderately effective in flash reduction. Initially there is oxygen inside the suppressor, which continues the combustion of powder particles. This combustion continues out the front of the suppressor. After the first shot, lack of oxygen in the suppressor limits the combustion process to the oxidizer in the propellant, and by the time of exit, the gas temperature has dropped enough so that there is not re-ignition of the partially burned particles on exit from the suppressor. The exception is with long duration burst or fully automatic fire (after 200-300 rounds) where the internal suppressor temperature increases enough so that the partially burned powder particles retain temperatures high enough to reignite on contact with the atmosphere.

There are no good ways to quantitatively measure flash for extremely short duration events, such as from firearms. Subjective estimates vary with the observer and his experience. What is probably the best way to evaluate flash and eliminate subjective bias is through photography.