Once upon a time I got a new kit and was very disappointed about some tom shells that were OOR. I did some research, including talking to the president of Pork Pie, and they all were consistent and teaching me that there is a variance/degree of acceptability for OOR shells; and in fact some of the best OOR vintage drums (including the majors) were and are OOR. My 12in was 2 mm OOR. It ended up sounding fine - tuned right up. Since have discovered others that were at least out that much and the factor that overrules that was the timbre-pitching technique that still made it resonate plenty.

So, 1/2 in on a 26 - might not be significant at all.

OOR - It used to really upset me - but it doesn't anymore. It depends on other factors that are more important I suppose.

Also - I have always understood that with a BD (and a larger drum) it (OORness) is less/least important.

If wood best put in water so that wood softens and then put a few metal Steel Round Tube Rollings to Form a compete circle in the inside so that wood take the shape of the round rollings. Let sit few days and drum back to shape. This what steel round tubing looks like you find it in big hardwares

Unfortunately it's out of round enough to prevent a head from fitting on it. I could live with it if the head was merely snug. On this shell, I couldn't even force a head to fit - it's that far out of round.