So, after over a week of sitting with seven shells in the extended (7+1) Choate tube with the shorter factory spring inside, I emptied it out to see how the spring felt. It was very weak, with light pinkie pressure needed to push the follower down, which I felt unacceptable.
I ordered a second Choate spring, which arrived today, to experiment with. Again, with it in place, the tube took 6 1/2 shells. I started big, cutting 2 1/2 inches off, testing it, then taking 1 inch at a time. It took removing 7 1/2 inches off the spring before I could get the tube to take seven shells. I also had to remove the black plastic reverse follower that was hidden in the extension. The spring is still longer than the factory spring and, when empty still has decent pressure.
The Choate tube is about an inch shorter than the SA-20 Tactical barrel. I wish they made the tube longer, close to even with the barrel above it; it would have given the spring a bit more room when compressed. I’m sure they had their reasons…