Yes, the slide bouncing like this has been suggested as the cause of problems. John gave a good description of what's likely to be happening some time ago.
Using the double capped W cartridge stops all the miss fires with mine. BUT I've found that the first cartridge in a full mag' doesn't feed cleanly into the chamber. The cartridge nose is slightly different in shape and gets stuck on the feed ramp. As a stop-gap cure, I've put one round in the mag, chambered it, then put the next 6 carts in the mag before inserting it into the grip. It'll fire and cycle all 7 then.
This gun cycles with a lot of force, especially with double capped carts. Having cartridges not feeding into the chamber is a worry, it must be putting a lot of force against the bolt face, slide and feed ramp. I'm planning on buying a new mag' then altering the feed lips a little to lift the cartridge' nose enough to clear the feed ramp.
The original magazine will be kept for standard cartridges.
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Cerwyn
Hobby collector of Replica model guns and Militaria.
also member of Living History Reenactment Groups.