Sorry, was interrupted yesterday and didn't finish the last sentence. It should have run "Buturlin's 24-bore Paradox by Matska, referred to in the DGJ Matska article, which is supposed to be built on the Ivaschentsev system but does have the rising bite as the top fastener."
Thank you all, it's very interesting. The heavy Parkers 20s appear to ba made as deliberate long-range weapons, and go even further in this respect than the Ivashcntsev-inspired heavy 20s which were made as all-around game guns.
I'll have to dig up Ivaschentsev's articles to give a deeper account of the original logic behind the heavy 20 thing, other than provided above.
On the practical side, the Sokol brand smokeless gunpowder, the most common one before 1917 and almost the only one widely available in the Soviet times, is a pretty capricious chemical - it really needs high chamber pressure to work properly and functions in small bores better than in big bores. Especially if you want to use light loads, 1 ounce or less, in the 12 gauge - hopeless. So for someone who is limited to Sokol and has to use both regular 12 gauge loads and light 3\4 oz loads, the heavy 20 is about the only way to go.
