Had some time to build something kinda stupid. After grinding out builds for UA customers for the last five months, there hasn't been much free time to try something different.
So, in the late hours at UA, I decided to scrounge around the office and put something dumb together.
TL;DR: Build Summary
(This is just the first test run. I'll retune it to run a tad cooler. There were also issues that will be covered in a future post.)
- Base Gun: VFC/UA M4 Midlength Carbine SSG
- Barrel: 280mm
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Performance:
- 425-430 FPS (0.20g) / 53.7 RPS (12.12V, 6000mAh 11.1V 16C Li-Ion 3S2P)
- *344-350 FPS (0.30g) in Full Auto
Internals:
- Gearbox: RA VFC GB 8mm
- MOSFET: Gate Titan 2
- Gears: RA Pandora 10:1 SSG (3mm) (4mm to be tested later) w/ SHS Cut Delayer Chip
- Motor: Warhead 52K
- Piston: UA 3D CF Printed (SHS Cut Rack)
- Piston: Head: Lonex POM
- Spring: Guarder SP150
- Cylinder Setup:
- ASG Ultimate Cylinder Head
- 3/4 Cylinder (doesn’t matter as the O-ring doesn’t pass the port)
- VFC M4 POM Nozzle
- Tappet: RA POM Tappet
- Trigger: Maxxpro
- Barrel: Prometheus Lapped 280mm R-Hop Barrel
- Hopup: Maxxpro M4A (UA Edition) w/ EMG Atlas Bucking
- Bushings on Spur, UA J-Caged Bearings on Bevel/Sector
- Lonex Piston Head
- Maxxpro M4A (UA Edition)
- EMG Atlas Bucking
...........................
I had some Retro Arms Pandora 10:1 SSGs sitting around for four months, so I figured it was time to finally test them out.
10:1 gears aren't new. I built a Siegetek 10:1 9-tooth DSG back in 2013, which pushed 410 FPS at 65 RPS—insane for the time. This was before HPA became mainstream, so dropping 65 RPS on a field turned heads. Back then, Umbrella Armory’s team had a reputation for running hyper-fast guns. Imagine 13+ guys in matching uniform, all fielding 30-60 RPS rifles in 2013. It got to the point where we had to split our team just to make things fair for walk-ons.
With today’s better parts, I wanted to revisit the concept—this time as an SSG. How fast can an SSG realistically go? At what point does a DSG become obsolete? I knew 40+ RPS was possible, but 12:1 SHS gears always felt sketchy, and Siegetek 10:1 SSGs are pricey.
First Impressions: Retro Arms PandoRA Gears
Having dremeled thousands of gears in my life, you get a feel for metallurgy just by how a gear cuts.
Gone are the days of cutting A&K MIM gears, only to find void pockets inside from poor pressing. Or Tokyo Marui gears that literally melted because they were made from something with a melting point close to silver solder. (Yeah, that happened.)
PandoRA Gears are machined exceptionally well. At first glance, the elongated and thinner tooth profile seemed weak, but their meshing does seem smoother.
The sector gear’s piston contact teeth are thinner in width, but the overall metallurgy is very strong. The way the thickness is distributed between the bevel, spur, and sector is clever—thicker where it adds flexibility and more tolerant to poorer shimming. It’s a great successor to Siegetek gears—solid build quality, lower cost, and a smarter tooth profile. I don’t expect them to fail under normal use. But let’s be real—we’re not testing “normal” here. So breaking them might just happen.
I short-stroked five teeth for this first test. This setup pushes the limits of PME (Pre-Mature Engagement), but worst case, my 3D-printed piston fails, or I kill the sector bearing, parts I do have replacements for, and even another set of the 10:1s.
To play it safe, I added SHS bushings on the spur, since 8mm J-Caged bearings always fail at the spur first when things go wrong (PME, bad shimming, jams, etc.). The Pandora spur was tight (common with SHS inconsistencies), but it wore in.
Fine-Tuning and Observations
Shimming
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RA Pandora gears have less clearance than SHS gears.
- Normally, I fit 0.9mm-1mm of shims per gear in an RA shell.
- With Pandora gears, it’s 0.6mm before binding starts at 0.8mm.
- This is similar to Siegetek gears.
Anti-Reversal Latch (ARL)
- RA ARLs are a stronger version of Modify’s ARL with an integrated pusher spring.
- Made from the same strong material as their gears.
- We’ve been using RA ARLs instead of Lonex ARLs, which tend to round out in high-FPS setups.
UA ‘Bert’ CF Piston
- We’ve used this piston for years, but recently made it standard in ALL UA builds.
- Lighter weight means higher FPS and reduced PME damage.
- SHS racks are insanely strong—haven’t seen them snap yet in specifically this, but seen plenty of the SHS bodies fail however.
Other Key Parts
- ASG Ultimate Cylinder Head – Perfect OD fit for VFC POM nozzles. No tilt, solid seal.
- Warhead 52K motor – Fast, hot, inefficient, but perfect for what we're trying to do.
- RA POM Tappet + PTS/MEC Tappet Spring – Testing how far RA tappets can go. Tappet timing has become an important factor with how well these can reliably feed and stay consistent. How they are cut, and tuned specifically in conjunction with specific short stroking methods is key.
The Results: 54RPS on an SSG?!
After programming the Gate Titan 2 and setting the trigger screws, I did the usual motor height tuning.
Semi-auto felt snappy.
Full-auto? I was kinda shocked.
I expected 45+ RPS, but was curious—could it break 50?
Chrono confirmed 53.6 RPS.
Battery voltage was 12.12V (not even fully charged).
435 FPS (Semi) / 409-412 FPS (Full Auto).
Holy shit. There IS room to improve however, FPS in Auto might be acceptable for most people, but it can be improved. For a first trial run, I'm pretty happy with the results.
So... Are DSGs Becoming Obsolete?
At 53.6 RPS, with an SP150 spring, this setup is far more efficient than a DSG.
- DSGs have terrible air volume.
- SSGs can run longer barrels without losing joules.
- No insane joule loss when switching to heavier BBs.
That said, heat remains the biggest concern.
- After 2 mag dumps and some semi-auto fire, the motor gets HOT.
- Not hot enough to trigger self-protection, but almost uncomfortable to grip.
To combat this, I’ll be adding thermal pads around the motor to help wick heat into the grip. I’ve also used G&P CNC Aluminum “Waffle” Grips before—they act as massive heat sinks but are a pain to work with.
What’s Next?
This build isn’t done. There were problems in stress testing, which I’ll cover in a future post.
For now, though—SSG at 54RPS? That’s a milestone. We do plan to sell this one off model.