I own two King 6B / Duo Gravis. One is gold brass, the other one is a Silver Sonic. Long story.

I was recently comparing the two horns side by side and noticed that the slides are quite different:

The Silver Sonic slide is narrower than a typical bass slide / Bach 42 slide. I'm measuring 3.125" width at the outer slide brace (between the oversleeves). It's also shorter than a Bach 42 slide, maybe by ~1 inch. The horn plays in tune for me with the tuning slide all the way in. I'm mostly a tenor player, still figuring out the bass trombone.
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The slide that goes with the gold brass horn is wider; I'm measuring 3.40" at the slide brace. It's an inch longer than the other slide. The horn plays flat for me.
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I'm also noticing that the inner slide tubes on the slide that goes with the gold brass horn are significantly shorter than the outer tubes.
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To add to all the confusion:

The slide for the Silver Sonic has matching 6 digit serials on inner and outer slide, but they don't match the bell.

The slide for the gold brass horn has a 3 digit serial on the inner slide, nothing on the outer slide and nothing on the bell. I know that there was a valve knuckle repair done on that horn so maybe the receiver got switched.

Does anyone here have an idea what may be going on? Were there different width slides for the Duo Gravis? Do I have a slide from another model? My assumption is that the slide that is with the Silver Sonic horn is the proper type slide for the horn but comes from a different instrument. I would not be surprised if the gold brass horn was a school horn and at some point got new outers that are too long. Still does not explain the width difference (unless the crook was also changed) as well as the tuning issue. Another thing that I'd like to find out is if I am playing my Silver Sonic bell with the proper slide :).

I have a 7B; the slide on those is wider and a

little shorter than a DG. It’s possible that is a 7B/8B slide, or at least a 7B end crook and they don’t trim the outer tubes properly.

The longer/wider slide has been made up from a non-matching inner and outer... the inner brace is from the orange lacquer era, and the outer isn't. You can see where the inner has been heated and widened slightly to match the outer.

Take the crook off the outer, cut the outer tubes down to match the inner tube length, and remount.