Wow, just wow. I'm familiar with Briley tubes to change shot gun gauges but not for changing a 12 gauge to .223. I'd worry about 1, the pressures and 2, how ya gonna aim it? What's the purpose?
Yes, they are rifled, but 7 in. long?? They are new, I would love to find someone who has tried them. They annot be very accurate, but in shtf, if ammo was scarce versatility may be appropriate.
Gunsites made a video about something similar last year. He had a video of him shooting a single shot 12g with the 22 die. I thought it was pretty nifty but nothing I'd purchase.