Umbrella Armory


Umbrella Prometheus 6.03 EG inner barrel with R-hop

Choose a Length
Choose a Lapping Service? (+$100)
~3 Week Build Time for some specific lengths.
Prometheus 6.03 EG inner barrel with installed R-Hop modification. Available as a stand alone barrel or with a pre-assembled drop in kit for compatible TM spec M4 type AEG/HPA Airsoft guns
The perfect upgrade for any gun, to increase accuracy, range and consistency of each shot fired. Out range anyone else on the field with incredible range and accuracy despite FPS.

Our handmade R-Hop has been an integral modification we perform for all our builds as users can experience 30% increased effective range over non R-Hopped barrels.

Purchase in a complete drop in assembly configuration for a true plug and play upgrade process if your build uses a Tokyo Marui spec M4 style hop up unit.

Purchase just the R-Hop barrel if you are planning to assemble it within a compatible hop up and bucking configuration yourself.


  • Inner diameter: 6.03 millimeter 
  • Polished finish
  • Precision, hand fitted R-Hop patch
  • R-Hopped glued into hop window 
  • Umbrella Armory specific R-Hop 2.0 patch design and material
  • Requires flat bucking and M-Nubbed / R-Hopped style hop up arm for use
  • Use .28 gram BBs or heavier to see optimal long range advantage over non R-Hopped comparisons


  • SUS 304 stainless steel inner barrel
  • Rubber R-Hop patch



What is it? Its a grinding method to microscopically remove material from the surface of the bore. Using extremely fine diamond compounds, we can remove material from the inside of the barrel that is uniform and consistent throughout the bore. Leaving a mirror-like finish that's very time consuming to achieve on a steel barrel.

As a result, the following happens.

  • ~2% increase in FPS
  • Increased shot to shot FPS consistency
  • Increased accuracy downrange
  • Easier barrel cleaning/less stubborn residue buildup

Below is an example of a Prometheus Barrel 6.03mm, pits, and bore marks can be seen within the barrel. With lab instruments we've measured this low/high spread as 5 microns. These microscopic holes tend to catch BB residues, and increase the internal friction of the barrel slowing down the BB.


Below is that same barrel with our lapping process done to it. We're able to reduce the internal bore surface roughness to below 0.5 micron. Resulting in a mesmerizing mirrored effect on the inside.

Recommended BB Weights

We prefer these weights for these muzzle velocities. For two main reasons. Best performance, and reliability. These BB weights will give the optimal range, and feed reliably. Going heavier than what is recommended may cause issues or PME if the magazine is not modified.

450-500FPS = 0.36g-0.40g
400-450FPS = 0.28g-0.36g
330-350FPS = 0.23g-0.25g