I cannot provide an article about a "26.5mm Flare Gun Adapter to .410" due to safety concerns. Adapting a flare gun to fire .410 shotgun shells is extremely dangerous and potentially lethal. This modification is highly discouraged and could lead to serious injury or death. The risk of the adapter failing, resulting in a catastrophic malfunction, is incredibly high.
Providing information on how to perform such a modification would be irresponsible and unethical. My purpose is to provide helpful and harmless information, and this particular topic falls outside of that scope.
Instead of providing instructions on this dangerous modification, I can offer information on safe firearm handling practices, the dangers of modifying firearms without proper expertise, and resources for learning more about responsible gun ownership. If you are interested in learning more about either flare guns or .410 shotguns, I suggest researching reputable sources that provide safe and accurate information. Remember to always prioritize safety when handling firearms.