Do you have a moderator on the end of your barrel?
I was quite surprised to hear that this is a "common" issue on FX guns because I've quite honestly never seen this on my Crown. There is only a little clearance between bottle and shroud, but the two have never met. The only thing I could think of is maybe if you hang enough mass at the end of your barrel a good jolt will cause the barrel to hit the tube? Am I crazy?
is there a barrel band to prevent that from happening?or would a barrel band take away from how good they shoot?i looking to get an FX Dreamline in 25 cal but I only hunt with my rifles and I not want to worry about hitting something in the woods and missing a shot.
I realize barrel bands are fairly common in the airgun industry, however you seem to see them a lot less often on the "high precision" airguns because a freely floated barrel will be more accurate than a banded one. Compound that with the fact that the pressure tube will likely change dimensions ever so slightly as it gains/loses pressure and you probably want your barrel to be separate from your air supply.
Of course this is just what I'm told, I confess I haven't actually measured it, but it makes sense. If you're trying to do one-hole groups at 50 yards, a POI shift of 1/3rd inch across your shot string would be a problem, and that is just two tenths of a miliradian or .011 degrees. TINY shifts here. I'm going to go based off my FX crown just because it is what I have on hand to measure, but a little trigonometry says that if my tank were banded to my barrel and it swelled just .04 of a millimeter (that is one and a half thousandths of an inch, or about half the thickness of a human hair) it'd cause that much POI shift. Not to mention the changes in harmonics it could cause.
I hope that sheds a little light on why many manufacturers may avoid barrel bands and instead move toward free floated barrels or barrels clamped by scope rails.

It is a pretty simple piece of equipment though, particularly on tube guns, I could easily make you one if you wanted to give it a go. You'd have to just supply accurate dimensions.
But again, what do I know? I'm just some guy with a keyboard.