Some additional information.
I can confirm the BT is 3" OD. I have the original LOC/Precision catalog I ordered the replacement BT from (since Estes at the time didn't offer a 3" tube). It was the BT-3.00 tube (3.00" ID, 3.10" OD) and originally, I had planned to replace everything forward of the original tube coupler with the new, stronger LOC tube, including a nose cone I ordered at the same time (PNC-3.00). However, the new NC was WAY longer than I expected, and at the time, I didn't know about any other options for a BT and NC that were available. So I was creative, cut out the old BT forward of the original coupler except for a little bit of a 'lip', then put some new BT on, then used the original BT that I cut as the 'top' part of the rocket. So what you see now is a Patriot with a slightly 'thicker' area near the top of the rocket that corresponds to the old 'yellow' collar. Anyway, the new tube JUST fit over the old tube (with a little sanding), so, yea, the OD of the old tube was 3".
Also, examining the rocket just now, I noticed my shock cord was REALLY short! No wonder it zippered...
FC