I had a similar problem with my .357 Mag barrel, but it was the lug welded on crooked and very crooked on the end the forearm mated to. The synthetic forearm was pretty tough stuff and I finally resorted to a die grinder after trying less aggressive methods!
IMO, there needs to be clearance on both sides from front to back.
I was shooting my .243 the other day and it looked like a house wren could make a nest between the forearm and the barrel, but it shoots good!
BTW, this is what I was talking about on the barrel lug not being flat. I did this in 2004 on
this 17 page thread.
OK, here's what I think I have found out. The barrel stud is the only thing making contact on my forearm. #1 son got after it today with a die grinder and relieved the material in the forearm to ensure it was free floating. After that we took some Prussian Blue and shot that in the forearm to see what was contacting. There was a very thin line of blue on the barrel stud and that was all! Maybe you can see this good enough to tell what I'm talking about.
The barrel on the left is the .223 barrel that has had the contact surface cleaned up with a file (the Prussian blue should be visible). The right barrel is the .357 and the contact surface is rounded so there is a very slight ring that is the contact surface. (I guess I had too much zoom for it to be very clear)
Here is where I have cleaned up the contact surface on the .357 barrel. If you enlarge it you can see Prussian blue all the way around the the widened and flattened surface.
This is both barrels side by side after both have had the surface cleaned up.
The problem with the lug being rounded was that it would allow the forearm to "rock" instead of being stationary. If it moves, all the floating in the world probably won't help, because the forearm can shift from side to side and that changes the barrel clearance every time it moves.
