A few years back, I wrote to Darne, in France, asking about their double rifle, and what they thought about using a Darne shotgun action for conversion to double rifle. They told me that their double rifle was in 8 x 57R only, and that it used special high strength steel, so they couldn't recommend the use of one of their shotgun actions for conversion to double rifle, because they use a lower strength steel. However, after studying the actions, I am not thoroughly convinced that their shotgun actions would not hold up to cartridges of low to mild pressures, and that is exactly why I am now in the process of converting a Darne 12 gauge (for added strength due to beefier action size, compared to 16 or smaller gauge), to 8 x 57R. By the way, a French made Charlin shotgun action, somewhat similar to a Darne, but much heavier and stronger, is more suitable for conversion work. Also, I am in the process of conversions using various other actions, most of them being German, but a few others. I took class on this conversion process, from W. Ellis Brown, at Pine Tech gunsmithing school, in MN, prior to his writing book on same subject, and I have since done many of these conversions, all successfully. His process works well, if done well.

No, because of aforementioned and other reasons, I would NOT use any Darne action for conversion to .450/.400 or .450 N.E. Use a more suitable action for conversion, German preferably, explained in Brown's book that you have. For those calibers, use only a 12 gauge; never use a 16 gauge, as they are simply too small and too light in weight for calibers you are thinking about.