Well, here I am again with the promised update. Had to postpone work on the Mossy for a longer term project. The failure to fire was fixed with a no-name, spare spring from a gutted old rifle that my 'smith had lying round. Very handy of them. Worked like a charm
Thank you Pine Rivers.
I continued to address the vertical stringing methodically, so I thought, by reducing the contact between barrel and fore end. carefully, wood was gouged out and the finish smoothed with coarse abrasive on a socket. Even more carefully, the barrel channel was widened just a little, so as not to leave too ugly a gap. Mongrel came with me to Belmont where we did a Lot of shooting. My results weren't too bad. Groups were a bit smaller, so I figured that in "going looser", I was on the right track.
The following weeks were spent on other things
to the neglect of shooting stuff but recalling past results, I checked the fore end and found a bit more work to do. Memory is hazy on this work but groups were from 2 to 3" and I wanted better. I kept recalling that in the really bad, strung-out groups, the windage was only 1". Rightly or wrongly, I was encouraged and motivated by that thought and the fore end was removed once again to loosen the fit in the front of the action. Remember, I was trying to be methodical; doing one change at a time so as to isolate the cause of the stringing but there was a catch. The rear barrel band screw was bent again. This was the replacement screw that had been sent Free. Then I recalled that loosening the Original screw was the cause of bending in the first place. Too much time had elapsed since the project had begun for my memory to cope with even this important detail. Asking for another one was Unthinkable so I did something else that was also Unthinkable and straightened it. Too bad if it broke. I had nothing to lose and it worked.
But now, there was a problem. Going loose was not the solution. Still believing that barrel vibration was bending the screw, I tried to think of what to do. I rejected the idea of a rubber screw
but later thought of installing an O-ring, to more or less dampen vibration. I was a bit hazy on detail but in almost no time, a ring had been trimmed and inserted between fore end and barrel.
Results at the range yesterday with some "working-up" loads for a new bullet, were Disappointing. The vertical stringing had returned. Loosening the rear barrel band screw in stages was ineffective but the loads weren't too hot as we progressed through incremental increases in charges. Another rifle was tested while the Mossy cooled, after every 3 shots. I wasn't taking any chances at spoiling this experiment by over heating the barrel. The front barrel band screw was tried after re tightening the rear but to no effect and 3 live rounds of maximum charges were left. The front screw was re tightened and the magazine cap screw was loosened one turn. The following group was 2.5" wide, 1/2" deep and close to the middle of the target. The vertical dispersion had disappeared
The rifle was put aside while testing continued on the second rifle, a rimfire, for 20 shots. It came to me suddenly that I had brought the remainder of the original ammo with me. Perhaps there had been the vague idea of testing it too but after changing to a fresh target, I turned the screw in, one half turn. What did I have to lose? I actually hoped that the horizontal spread would shrink a little, even if it increased the elevation. The next two shots were dead level horizontally, right at the very top of the target. Carefully, I inspected the backing board in the area above the group making a mental note of the holes that were present, so as not to confuse them with my next shot. But it was not to be. The RO called a ceasefire
Hmmm. Patiently. I waited while a target change ensued and the third shot, when it happened, formed a group, 1/4" deep by 1.75" wide. Oh Happy Day.
That is two bullet weights and no vertical stringing. That can't be a fluke, can it?
But here's a thought. That final screw, the magazine cap screw, makes no contact with the barrel. As pointed out Very Early in this topic, the is a blind hole in the underside of the barrel to accommodate the nose of the screw but it makes No contact with the bottom or sides of the cavity. I had forgotten that too. Had I recalled it, I would not have touched it. This gets back to postponing work on projects, only to resume long after the results have been forgotten. So does anyone know why the last screw worked?