Browning made threaded "choke tubes" which seemed more like barrel extensions, up to I think 4" long back in the '90's.
Threading two barrels is a far simpler approach than sleeving two. Of course if it's a vintage platform, a steady diet of heavy loads will show sooner or later.
I'm finding my scores are improving with 24g loads and 32" FxF barrels. And the fatigue lessened. But I'm not shooting M class either. I only give up performance on close stuff. The long stuff is refreshingly delightful to shoot.
The heavy gun makes you really think about set up.
