I've managed to unsolder the barrels. It seems Pedersoli brazed them with some sort of yellow looking high temperature braze. The alloy let go around 600~650 deg C. I have a propane forge so I ended up opening forge doors so the barrel could pass through under a burner. I heated parts of the barrels to around 600 deg C (monitored with a contactless thermometer). Then after pulling the barrels out and putting them on a steel table I quickly hit the rib with a small propane torch that brought the temperature high enough to melt it in a small area.

If this was normal carbon steel I think heating the barrels to 600 degrees C would ruin the surface due to oxidation. However I found out previously Pedersoli uses 30CrMo4 (chromium manganese steel). Thanks to high chromium the surface is somewhat protected. I also checked that this steel will not be weakened by heating it to 650deg C Its usual tempering temp is 650c - it anneals at over 800 deg C. This is probably why they chose it.

You can see on my picture how unusual grey color the steel has after. Normal carbon steel would've looked a lot different.