Pilgrim:

I would strongly suggest that you discontinue shooting the Barnes X and Solids is your gun. Barnes doesn't make a bullet that is appropriate for double rifles. Double rifles are intended for use with conventional lead core bullets. I've had personal experience with a 9.3 wrecked with Barnes X and the solids are worse. The Chapuis 9.3 is of particular concern because the barrel walls are quite thin, and I know of a Chapuis that had barrel damage from the X. I'm pretty sure that Chapuis doesn't warrant their barrels for use with monos. I'd suggest that you read some of the old strings here about using mono-metal bullets in doubles.

I tinkered with the 300 grain Swift A Frame some years ago, and I would caution you to avoid it as well. It has a homogenous section in the middle and the shank is very hard. Woodleigh makes some fine 9.3 bullets that are perfect for your double.
------------------------------------------------------------------------------------------------------