Whoever said DMRs are cheap?
A TK barrel does not offer a simple solution. It was designed for the Japanese market and their crappy velocities laws. DBC tried to create twist barrels for the US market and they ran out of cash years ago.
The TK barrel performance from what I understand is finicky at best. If it works with at 328FPS regardless of joules then we are talking about something else and I have not heard of anything to support that. From what I have heard ever since they came out is that they work at 1J or 328FPS w/ .2g BBs not just 328FPS. BIG DIFFERENCE! If that was the case you could use .28g BBs in almost any stock ACM AEG with a TK to get the expected results and I'm sure if this was true we could buy them anywhere. Like I said, the simple fix requires $200+, sweat, blood and tears.
Cheap route from scratch:
Semi-only selector plate mod unless your local field allows full-auto for DM like mine.
$8 for another selector plate
$15 KWA 2GX hopup bucking
$60 TBB (ie Prommy 509mm 6.03)
$5 shims (Modify or Prommy set for very close shim jobs)
$15 Bearing spring guide
$15 Prommy MS-135 or other other 450FPS spring
$50 G&P M160 motor or another neodymium magnet motor (matrix is cheap but not as good)
$40 Prometheus Hard type piston (still need to correct AOE)
Should be near 17rps which is enough for a quick trigger response.
Thats pretty close, you need a battery if you don't have a 9.6v large battery and I'm assuming your gears are not poopoo. I'm also assuming you do not have a 7mm MB or plastic bearings.
But yeah, after you can get the system running then you have the headache of getting the most out of it and getting the velocity consistent enough to place shots at range.
Add a active breaking mosfet later and rewire your gear box with 14ga wire at the same time. You could also switch to Deans Ultra plugs.