For that kind of thing the steel is going to be 4130, In theory one could externally butt it on a lathe, though whether it's worth the trouble would depend on the application.
The tube would weigh about 103 grams for the 180 length, and you would use a little less than 180 to get 180 C/L. assume around half that length and twice that thickness for the two collars, and you have another 103 grams. Then you have the fillet in either TIG or Brass, and the compression nut assemblies. It could easily go 250 to 300 as suggested.