As you can see from the pic above, pasting with comments is something that I have not mastered HOWEVER, I have fixed this freaking damn gun
Much of the credit must go to In2anity who posted his work on a Marlin 336. His reference to the book by M L McPherson was invaluable, in the end. By that, I mean that bedding my fore end in RTV did not work at all, in reducing vertical stringing. It should be said right here, that all of the mods performed by me over the years might not have acted in my best interests. Yes, this is damn complicated. To simplify, In2anity's fix might have worked had I not hollowed out the fore end, relieved the barrel channel, yada, yada, etc.
To cut a long story
short, after failing initially with the RTV, I went the Whole Hog with McPherson's Method and added the RTV between the front and rear barrel bands and ran a bead of it between mag tube and barrel, from action to muzzle.
THAT made a Very Big improvement immediately. The mag tube stayed in place
That's a plus, eh?!
The above pic does not reflect that huge leap, from 6" to about 2". This pic above was of last Saturday's testing at 50 yards where I tried to reduce the string further. Shots 1,2 and 3 were fired with the Rear Barrel Band Screw in the same position (firm but not Really Tight) as it was last month, 24/1/20. The rifle grouped about the same; no surprises there.
Shots 4,5 and 6 were fired after the FRONT barrel band screw was slackened by 1/4 turn. Still plenty of vertical. The rifle was being cooled between 3 shot groups so the barrel would not heat up too much.
Shots 7,8 and 9 were much better from the point of view of string. I blame #9 on the terrible trigger. The rifle cooled during a target change and 10 and 11 were fired. That was the end of the ammo. The group 7 to 11 is only about 1.25" deep. That will do me