I was cleaning up around here and found my old "Adjustable Sphincter" project.
So noticing this thread and being a simple man of simple means who likes shoving things into other things, I grabbed some old TL barrels, one of my detents, and shoved one in the other.
Surprisingly, it actually almost works.
If it were me... well for starters I wouldn't get so weird about barrels because, I mean, come on. It's a barrel.
But it might be possible to tweak the design to still work with the TL barrel as-is. It would need to be a bit more aggressive to deal with the fact that the mag detent slot is slightly forward of the ball. Either that, or the through portion of the slot needs to get about 2-3mm or so closer to the bolt, right to where the center of the ball will land.
And then in either case you'd need a stop at the front end to keep the detent from walking forward (i.e. a drop of silicone glue or something). Or maybe extend the detent so it stops at the o-ring.
Personally, I like dual opposing detents but whatevs. Can't really do nothin bout that without no power tools.
"Accuracy by aiming."
Definitely not on the A-Team.