If you have a Gen 1 SpringPheed and want to upgrade to the latest generation, you can send your tube in to me for the proper milling. The cost of this service is $10, plus the cost of the desired mounts and return shipping. Please contact me for more information.
Note: All Gen 3 and newer mounts are standard height, so you will need to install the standard front ring if you have a Low mount.
I have posted a video of the steps required on my Media page, but in a nutshell:
For Gen1 tubes, you will need to make a square cross-sectional cut right at the front of the mounting screw pass through (top) hole. Then, using a rotary tool or hacksaw/files, you will need to extend the plunger slot all the way to the end of the tube.
For early Gen2s, all you need to do is extend the plunger slot to the end of tube using a rotary tool or hacksaw/files.
To fit flush with your barrel, the overall length of a properly milled Gen 4 tube should be your barrel length minus 3/8". This is excluding the end cap.
Replacement mounts for the Phantom platform can be found here.
The cost of the mounts can be calculated by subtracting $64 from the cost of the desired Pheed and any accessories. So for Gen3 ($85), the cost would be $21 plus shipping (~$4 in the US). A standard height mounting ring and screw is included. If you need additional rings (i.e. for different barrel diameters), they are $3 each.
The mounts include all necessary hardware and parts to work with your existing feedtube, except the plunger assembly, plunger spring, and front cap assembly.
Note: From Gen 3 and onward, all heights are standardized; there are no low mounts.