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DSG barrel length and FPS

1013 Views 16 Replies 5 Participants Last post by  Leo Greer
I am currently working on building my first DSG and was curious if anyone else has run into this weird issue or can explain why what's happening.
I have almost identical fps on semi with a 168mm 6.01, 275mm 6.03, 325mm 6.01, and with a 416mm 6.03, all at around 360-375 fps (.20s)

Current Build:
SHS 18:1 DSG (8tooth)
G&G 18:1 Bevel & Spur
SHS swiss cheese piston (teeth cut off, 3rd tooth lightly shaved down, AOE corrected)
Lonex Aluminum Piston Head (bearings removed, spring guide has them)
Lonex Full cylinder
Lonex Cylinder Head (one with the pads at the front of the gearbox)
Retro Arms 8mm GB
SHS Meteorite bushings
Maxx 21.25 nozzle (2nd o-ring removed)
Tappet plate cut to 10mm (Not sure what brand but starts 2-3mm later than the long SHS tappet plate)
Strong tappet spring cut 3 coils
ASG 30k (not the fancy CNC)
Perun Hybrid (in DSG mode, no AB in semi, lvl 3 in full auto, no precock, no ROF control)
Maxx ME Pro Hop-up
R-hopped 6.03 275mm
G&G green (nub cut)

I am also still working on full auto fps loss with more powerful batteries,
7.4v 2200mah (25 or 35c, cant remember) shoots ~32ish rps at around 330-340fps
Titan 3000mah 11.1v (I believe 15c) shoots ~41ish rps also around 330fps
But my big 3000mah 50c has reached a high of 52rps on the chrono, but skips and misfeeds usually around 280fps, sometimes after a burst on full, the last bb will roll out of the barrel
Did I make my tappet too short? Is it still too long? Is my tappet spring too strong and pushing the bbs out of the hop into the barrel?

This only happens using the larger battery on full auto, semi still works great feeding and fps wise with the larger battery.
I was using a lonex m150 spring and believe I was hitting PME on full with the larger battery, tried a matrix m160, which bumped around 20fps or so using the 6.03 275mm (usual barrel I run with the gun) compared to the m150, putting me at around 375fps. This helped with the overspin using the larger battery and I plan to use a guarder sp150 when it arrives to further cut down overspin and hit my target fps.

I want to be at 400fps with .20s and will get a smaller barrel if need be, however when testing the smaller barrels, I still had the same fps. What is going on??? Am I under-volumed like crazy? Over-volumed somehow?

To note, I played with the DSG with the m150 and the 7.4v around 30rps and cycled 10k+ rounds with no wear on piston teeth, 11.1v big battery arrives, test in full auto (around 100-200 rounds or so) to see big drop in fps, open gear box and visible wear on the piston teeth. How strong of a spring do I need? I believe a Guarder SP150 should be plenty. Should I swap the aluminum piston head for a Lonex POM piston head? A gate EON POM piston head?
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168 6.01 is ~4.7k mm3, 416 6.03 ~11.8k mm3: if you don't see any change in FPS from more than doubling the volume of your barrel that's... weird. Full cylinder, could be over volumed for the 168, under for the 416 - and somehow the resulting fps is close enough to be confusing?

FPS loss in FA with a DSG + strong battery is almost certainly PME but can be timing related / tappet plate isn't quite right. How did you trim your tappet? Arbitrarily 10mm, or did you find the optimal release point?

Yes you should swap to a POM piston head - Lonex POM or Laylax NEO POM would be my suggestion. Do you know the weight of your piston assembly? For anything over ~40rps you want to get the complete assembly under ~20g, the lighter the better. Alternatively can bump the spring up and loose some barrel volume or run a ported cylinder. Maxx type F cylinder + sp140 +147mm 6.03 shoots ~340fps with good seals
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8t DSG will retract the face of the piston to the back-end of the ports on a Maxx type F; I run them in two of my DSG builds. The port allows the piston to accelerate before making compression which helps get it home quicker if you have excess volume, gives you more headroom for PME. Also seems to improve fps consistency by a small amount, speculate this is due to the oring seeing a sharp pressure spike when it passes the port vs the pressure ramping up as the piston accelerates.

Tappet being to short would reduce the stroke and dwell of the nozzle, so yes - should only cause feed issues. If it's to long though, the dwell of the nozzle is extended which can result in it not having enough return time between shots - reducing fps. Every gearbox, gearset, and tappet is a little different; need to find the optimal release point for every combination. The shape of the fin after trimming is important too, if the angle is wrong, the roll-off to sharp or to gradual, can lead to all kinds of weird issues. I can share some references later if this would be useful (on mobile atm)
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Found some previous posts to bounce here. Blue fin shapes below are how I shape my fins and fine tune them, but need to understand why - a sharp release vs a controlled one, BB seating, etc - review the thread those comments are in for details. Red tappet was done in a hurry. Excess grease applied to check for rubbing- not run this way.
Shouldn't need to touch the front of the tappet unless you've got some weird tolerance stacking going on. When I trim the tappet I open the gearbox, take the mainspring + tappet spring out, spin the gears by hand to manually pull the piston back, and adjust the tappet length such that it 'releases' when the piston is in contact with the last 1.5 - 2 teeth on the sector. Very small adjustments after that if feeding issues. If using active breaking on a neo motor might need to shape the bottom of the tappet slightly to avoid the opposite 'pickup' pin on the sector from crushing it.
The above trims the tappet to the correct length for your particular gearbox, whatever that length may be. Trimming the tappet an arbitrary amount such as 11mm might work, might not - it depends on tolerances, part selection, etc etc.

Basically, 11mm is an 'educated guess' whereas doing it this way is 'how to find the right length'
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I'd suspect PME. Could try the paper test to check your nozzle seal but in FA the vibration might shake it loose just as quick as a leak. Generally the way you check for PME is to try a weaker or discharged battery, then slowly increase the voltage/charge to see if the fps is good then gets bad - if so, indicates piston is catching/PME. 30fps is a lot to loose, might run for a while but parts will fail prematurely from the abuse. 5ish is about what I expect from a DSG.
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I use silicon 'gel' in the cylinder and on the piston head oring, is lighter / has less resisance than grease but doesn't get shed as quickly as oil. For gears, rails, etc, I use a THK AFF grease. Tippmann makes a nice little 3 bottle bundle that has the gel I like and a veriant of the same grease if you're in the market Tippmann Tactical Airsoft Lubrication Kit | Pyramyd Air

For the magnet holder, the triggwe pin holds it off there when the gearbox is together
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