Viking, there's a couple things to do, some of which are for a smith.
First, some 11s were chambered for ammo shorter than what we use now. A smith can tell by measuring the chamber, and while he/she has it, have them deep clean the action. Browning designs are famously overbuilt, but tolerances are tight and there's lots of little parts in there. While you're at it, have the smith install new springs and friction pieces,keep the old ones as spares. Browning A5 parts will interchange, at least these will but not others.
Inside the forearm wood is probably a diagram of how the friction pieces go together for loads of various power. If not there. mayhap someone here will post a link.
Once running, stick to 2 3/4" ammo.These are not magnums but are fine old workhorse shotguns.