Ithaca introduced the Flues model around 1908. Smokeless powder had been available for at least a decade & a half by then. No doubt Ithaca considered the fact that the Flues guns would be shot with Smokeless when they made them. Standard 20 gauge load of the day was 2 drams or equivalent of powder with 3/4 or 7/8 oz of shot. Later a "Heavy Field" load was offered with 2˝ dram equivalent powder & an ounce of shot. With "Progressive" powders in the 1920's an "Express" load was offered with 2 3/4 DE & 1oz shot. No doubt these heavier loads cracked a few Flues frames & split some stocks. This was not however due to the increased "Max Chamber Pressure" of these loads but due to the increased payload of a heavier shot charge at a higher velocity. Same thing that makes it "Kick" harder. That Harder Kick puts more strain on the action as well as the stock.
Barrel bursts have not traditionally been a problem with the Flues to the best of my knowledge. When "ANY" shot barrel does burst down around the forward hand then it probably didn't matter a lot which load was being fired. It could have been a flaw in the steel or could have been some sort of obstruction. A through investigation would need to be done to determine the actual cause.
