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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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I find the voluming explanation most likely. If you!re overvolumed on the shorter barrels and undervolumed on the longer ones it could be just enough of a coincidence to seem weird.

Alternatively, is it possible that the air seal isn’t consistent between barrels? I don’t know how much experience you have putting these setups together, but sometimes the tiniest things can affect everything in a big way, especially when it comes to tuning your hop system. It would be a big coincidence, but not impossible.
Most barrels tested are patched and I used the same bucking (G&G Green) with cut nub for patched, and a brand new G&G green for the 168mm unpatched (only one not patched). I just tried the 168mm without my upper for the 275mm barrel and lost ~10fps, but that could just be due to the fact that I'm trying to push the hop into the gearbox. Same hop-up used on all barrels with same spring. Any ideas on the full auto inconsistency on a larger battery? Could it still just be causing me to hit PME with the M160?
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
Even with the DSG short stroke would the piston ever come back to the port on a type F cylinder? Based on what I had seen with other builds it seemed pointless and just another way for the gearbox to collect contaminants. I believe I'm still hitting PME with the m160 and am going to go with a stronger spring and swap to a POM piston head and see if that helps. I had trimmed the SHS tappet down to ~11mm based on optimal release point, then I was having issues even with <30rps on full, and saw the SHS tappet pulls back slightly earlier than most other tappets I had, so I tossed a different one in and also cut it to 10mm as I figured my mags would still feed and shorter tappet should only hurt feeding correct? My midcaps feed my HPA fine over 60rps so I figured this wouldn't be an issue and would only save me a GB opening.
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)
Good to know about cylinders, guess it would help correct PME after one shot as well having the cut out to let it return to a non PME state faster, which would at least cause less damage if hitting PME. My tappet may have too sudden of a drop off so I will try rounding the front edge later. My tappet seems to be cut perfectly for 30-35rps or so, with very small full auto fps loss. Is around 30fps an ok drop for FA or can I improve it? Could my tappet however still be too short for ~50rps, just due to cycling faster? Or am I just hitting PME on the larger battery, possibly with a tappet that is sufficient. If you could post some pics of a well rounded tappet so I could see what I "should" be aiming for, granted it works in my build...
Are there any simple tests I can do to check where I am losing the FPS in FA? Whether it be tappet timing, nozzle too strong/weak, or PME?
Check to make sure friction between the piston head and the cylinder are at a minimum. I’ve dealt with a couple of cylinders that have been too small for regular piston heads, and have caused PME as a result thanks to the slowed piston return.
Yea with an SSG I found a Maxx cylinder to be much tighter with the piston head I was running, hence why I just went lonex/lonex this time around, and it seems to be riding quite smooth, not too tight but still a good seal.
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I'm suspecting PME, especially due to the sharp wear in the teeth when using the stronger battery. I tested the batteries how I got them out of storage and then full charged and on the stronger batteries it got even worse, and wouldn't really feed properly. Do you let your trigger magnet holder rest on the post of the Perun? Or should I use the front set screw to bring it off just slightly?
Just to be sure, what grease do you recommend for the gears, and what for cylinder/piston head o-ring & nozzle/cylinder head?
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