From memory, I use different holds for the Webley (Tempest/Hurricane). With the Tempest I use a firm grip with my shooting hand, not support hand. With the Diana LP6M/LP5 magnum the other way around. I squeeze with my support hand.
Thumb position was also crucial with both (bent or straight) but dont recall it. Havent shot them for long.
With these holds, both guns are véry accurate. Ragged holes at 6 yrds. My best with Tempest 1 cm edge-edge. Which is kinda standard for the Diana.
Consistency...dont know. Tried artillery hold long time at first, just didnt work. Than got a tip about firm hold for the Tempest. Now shoots like a dream.