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Ended up using a bit of ammo to get the bottom barrel "regulated" by shooting to the point of aim and the top barrel, still crossing and low by about 6 inches at 100 metres.

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The right way to regulate these bbls is to get the two bbls shooting in the same place (any place) first, then adjust the scope second. You should be able to get it pretty close with less than one box of ammo: one pair to see where they are, two pair to get the horizontal right (you can make an initial horizontal scope adjust after these), two pair for the vertical regulation (initial vertical adjust on scope), and two pair to finalize the scope. This should get you to a point where you have confidence in the rifle for hunting use, and as good or better than 80% of the fixed regulation doubles out there.

The problem is these guns are capable of bolt-action accuracy. Mine shoots bona fide 3/4" composite groups at 100. So some folks are tempted to twiddle this way and that to get them just so. If you are one of those, plan to use two boxes of ammo.

In order for the bbls to cross, the bbls have to be bowed apart at their midpoint. This means the wedge has to be tightened not loosened, as another poster pointed out. If the lock screws went loose on you, the wedge would have slipped and the bbls would have moved toward each other, causing the shots to diverge rather than cross (top shooting high, bottom shooting low), not the opposite.

If you look at the design of the wedges, the front wedge (for horizontal alignment) is held between two opposing screws and is very unlikely to move once set. The mid wedge (for vertical alignment) is a clamp that grips the lower barrel and at the same time an angled dovetail SOLDERED to the top bbl. As you move the clamp in the axis of the bbls, it forces them apart, bringing the top bbl POI down relative to the bottom bbl and vice versa. The whole assy can't slip on the bbls...but the wedge can slip if the screw is not tight. If it does slip, it will probably slip to a neutral position, ie no force separating the bbls. This will cause the bbls to diverge on the target, if the initial setting involved any degree of bowing apart.

For peace of mind, use some epoxy on this mid-screw once you have set the regulation. For even more peace of mind, put some on the dovetail as well.

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