there are two thread types for the tippmann A5,
the first one being the normal screw type thread everyone is used to (the same kind of thread thats on the other end of hte marker, where the bottle screws into [but obviously not the same one, acctually, ive never tryed screwwing a bottle into the front of my marker... so i could be wrong
])
the second type is the one that your flatline has. which is a completely different type of thread to your normal one. its has two raised areas inside the body of the marker, where the barrel attaches.
on the flatline itself there are also 2 raised areas (im crap at explaining this sorry), when these areas on the barrel line up correcty, you push the barrel into marker, and the two raised areas (or i suppose threads), go past the ones in the marker body,
you twist it 90 degrees, that locks it in place because the threads inside the body are now in the way of the ones on the barrel.
So obviously, getting it off just means simply twisting it and pulling it out.
If it doesnt come out you simply have to either:
1)twist it furthur, cos its still locked
2)pull harder you weakling
3) losen the screws a bit more.
Once you have the flatline removed, and your going to attach another barrel, you might need an adaptor. As the system that the flatline uses to attach to the marker body means that the adaptor which normally comes pre fitted needs to be removed, you might not have it.
Unless it came with the stock barrel.
In which case ity will probably still be attached to that.
This is has the same thread on the outside of it, as the flatline does which goes into the markers body,
then on the inside it has a typical screw thread. which allows you to use other barrels.
If you havent got this adaptor, your either gonna have to buy a barrel which has the flatline style thread,
or get a new adaptor.
hope this made sense. it did in my head as i was typing it
lol.