Thanks gentlemen.
Matt: the gun is a 1920s hammerless boxlock, so nitro proved.
The 'modern' load I use is 33.5 gr Blue Dot.

Rockdoc: would kill for a WR Explora these days, especially the 'Super-Magnum'. Hard to find any examples for sale, let alone affordable!

I have always found poverty easier to live with than regret!