Hello April,
I just came across your topic and it was interesting for me to read it , since I recently finished a DSR3 core.
First of all I am sorry, that the core didn´t work as expected, and I hope you found a workable solution.
One thing that catched my eye is the picture of the door frame, that you posted (31pic). There seems to be a mistake in following the original DSR3 design, that might be crucial, the slots for the air intake on the left and right side should be in the upper half of the core. Looking at your picture, they look like going down almost to the bottom of the core. Peter mentioned several times, that this is crucial, and with the slots that low, it would be more prone to run into thermal overload, at least I understood it like that.
Another thing, you have a large bell! Do you have a bypass? Like a shortcut for the flue gases, that they won´t cool down that much before they enter the chimney. At least when the bell is cold, such a bypass might be crucial for the fire to come to live. The chimney will provide more draft, when the flue gases are at temperature, and the temperature before entering the chimney should be at least around 200 F.
I hope you have a good working stove now, but for the case you are still on the journey, these things might help you. I want to believe, that a DSR3 design can work fine with a rectangle afterburner instead of a tube, but I didn´t try this. I could fine tune my core very easy with diminishing the space inside the top box by putting inside some refractory leftovers to calm down the burn a bit.
