Classic obstruction burst.
Absolutely, "NO" signs of an obstruction. An obstruction will show a bulged area like a snake swallowing an egg & then if it bursts the bulge will still be visable in the edges of the burst. This is a clean longitudinal split. I also Very Seriously Doubt steel shot had anything to do with this burst. Was likely not the result of a "High Pressure" load either as is too far down the bbl. Pressures are remarkedly similar once you pass the chamber, & if the load had similar ballistics the pressure curve normally crosses at about the end of chamber, thus a lower "Peak" pressure load would have more at this point. Looks much more like an internal seam in the steel that just finally gave way.
