I have never had to "tweek" the barrel on a pinned S&W, so I cant say how that would effect things.

I have done so to several fixed sighted SA revolvers with excellent results. Both required at least as much of a turn as yours appears to need to get things hitting POA. The cylinder gap change was minimal, having no negative effect.

I am not a gunsmith, but I believe the small amount of correction your barrel needs should not be enough to have to worry about the barrel shooting loose. I would try it, and worse case situation, the barrel starts to loosen upon use, or the retaining pin wont properly fit, and you have to go thru the effort of having the barrel shoulder turned down, and the barrel re-fit.

Nice looking 1950 Target, by the way.

Larry