Using Trail Boss has the affect of eliminating or substantially reducing the effects of barrel timing, because it burns so fast, yet with low muzzle velocity and at relatively low pressure that barrel vibrations are nearly gone before the bullet exits, and muzzle blast, again because it burns so fast that there is very little pressure remaining at the muzzle.
Using this method, you should be able to substantially isolate the variable of OAL to find what your gun likes.
Once that's done, use the standard Newberry method to find Optimal Charge Weight.
That's interesting, so basically COAL and powder charge are not related under this theory.
I like Newberry's method for finding OCW, I guess I've been using a modified method, but will give what he says a try using the round robin approach. I also notice Newberry isn't to concerned about finding a optimal COAL.