No, I'm not going to send the ATF a barrel along with another piece of pipe insulation. It isn't necessary. I gave them a very clear description of what I wanted to use it for and how I intended to install it. They know that it fits tightly over my barrel and doesn't fall off. They know it's not permanently attached to the barrel and they know that the barrel of most paintball markers are detachable.
If you think about it there is good reason in the 2004 case for the barrel being welded to the marker. If a silencer were permanently attached to the barrel but the barrel was removable then some enterprising individual would manufacture some accessory for a firearm, a laser sight perhaps, that attached to the gun using a mounting that just coincidently used the same thread as the paintball barrel. The next thing you know lots of these accessory's would be purchased along with a paintball barrel/silencer and people would have two readily obtainable legal components which if combined would make for a great silencer. The people at the ATF are not stupid.
If someone wanted to use a piece of pipe insulation on a portable firearm (the ATFs terminology) they wouldn't need the paintball barrel. They would just wrap their gun barrel with tape until the insulation fit. The paintball marker is simply not part of the equation. What you do with a piece of pipe insulation is of no concern to the ATF until you attach it to a portable firearm, at which point you are in violation of the law.
Besides, the genie is out of the bottle, why give government an opportunity to put it back in? My 2 cents anyway.