Airsoft G36 barrel mount stabilisation block - parametric

Improvements

Improvements 4. 5. 2026

• More photos of other details of the weapon. Inserts for removing various clearances in the weapon, mostly made of CU.

• The dimensions of the inserts work for my airsoft gun, yours may need different ones.

• Frame reinforcement, glued metal frame to plastic body, on the left side where there are no screws. Mamut total glue, white. Degrease, thin layer (you don't want to deform the body with too much glue), press with a flexible spatula, because my body can't be disassembly in half. Press with clamps overnight.

Improvements 14. 4. 2026

• Expanded aeg parts upgrade advice text

Improvements 30. 12. 2025:

1. Additional separate part for of the mainbody v 1.5.2 for better fixation of the AirsoftPro CNC G36 hop up chamber as it is designed in the mainbody v 1.6.1. It can be additionally added for the mainbody in 1.5.2, personally tested and mounted. The axis of the barrel - nozzle - gearbox is now better a more stable :) 

   1. Procedure:

      Assemble the hop chamber including bucking, hop chamber centering ring, barrel lock, inner barrel

   2. Slide onto the additional part and into the mainbody, this should center the additional part on the mainbody

   3. Glue the additional part to the mainbody with glue, wait, remove the barrel with the hop chamber. Since I have everything printed from PLA+, I glued the additional part with gel superglue.

   4. Secure the glued joint with 2 self-tapping screws of the appropriate size, just for sure.

Improvements 23. 12. 2025:

1. Text fixes

2. Notices expanded

3. Barrel lock model

4. New model version. Mainbody part v1.6.1 - 5 millimeters longer on the hop-up chamber side and with a smaller hole for the hop-up chamber, according to the dimensions of my AirsoftPro CNC hop-up chamber. So that the hop-up chamber is tightly inserted and embraced by the mainbody for the first 5 mm. I assume better mechanical strength of the mechabox - hop chamber - mainbody assembly and better weapon axis. + Trimming excess material on the top side. Not yet tested in real life.

Description

Replaces the original outer barrel mount/holder with a much more solid shape. Prevents lateral movement of the barrel. Increases the accuracy of the airsoft gun several times.

FreeCAD file included.

Tested on SRC G36E2 gen. III:

Needed airsoft parts / parts in my SRC airsoftgun

• Airsoftpro CNC hop-up chamber for G36, red color (tested) or CNC hop-up chamber from another manufacturer with screw connection to the gearbox (not tested!).

• JJ hop-up chamber JA-3602 as a donor of small blue plastic parts, because they have a more accurate shape than some original plastics from airsoftpro chambers, or better.

• ASG ultimate cylinder head for gearbox v3 or better (EPES recommended). In any case, the cylinder head must be well fixed in the gearbox.

• Retroarms (length of 25.2 mm was too long for me, It stretched out the hop-up bucking in just six months.) CNC nozzle or better.

• Hop Up bucking 4UANTUM AEG orange with nub or better.

• 363 - 415mm inner barrel, Specna Arms stainless barrel (it's actually the same as ZCI) or better. See notes and table below. I agree with the actual information on the internet that 509mm for a standard full cylinder for AEG is outdated and too long.

• Padding the clearance between inner barrel against the outer barrel, for example with plastic strip of suitable thickness.

• Standard gearbox SRC v3, or better. (Beware, original SRC gearbox has has less space for wheels and piston upgrades. Personally, I had to replace the gearbox as well, now I have an SHS QD with a microswitch, but next time I would rather try Specna arms QD with microswitch or Retroarms CNC, after verifying that they fit in size)

• Other common upgrades

• Another piece of long outer barrel SRC, outer diameter approx. 16 mm

• Moved the battery to the rear, into the stock. Rewired and diy MOSFET board or better

Notices for upgrades

• Hop Up bucking 4UANTUM AEG

  • The 4UANTUM HOP bucking lips are too long for the Airsoftpro hop-up chamber (as well as the Maple Leaf buckings), they protrude too far into the feed shaft and there are problems with feeding the bbs. So I sanded the lips - shortened them by about 0.3 mm. Sandpaper 600 → 800 → 1200, all with silicone oil as a lubricant. The option to attach the rubber band to a piece of old inner barrel and attach the whole thing to a standing or hand drill is an advantage, the speed of rotation is max. 500 rpm. so that the rubber band does not melt instead of grinding.

  • Do not use pads under the hop-up bucking, because this would shift the cutout for the barrel lock in the hop chamber and the barrel would then press on the rubber band and deform its shape, which would worsen accuracy or bbs feeding.
     

• The hop chamber blue plastic pressure element for hop nub may be too high,

  • It was necessary to reduce its height with a round 3 mm hand file, using precise movements and deepen the round groove for the hop-up rubber pressure. On the blue part from JJ Airsoft, it was necessary to reduce the height from 3.45 mm to 3.15 mm from the top of the arc, to be able to completely turn off the hop-up in the MIN position. Without adjustment, the 0.30g BB pellets were still too over-hopped even in the MIN position.

• Inner barrel lock in hop up chamber

  • The inner barrel must not move in the hop-up chamber, especially not back and forth. This can cause compression of the hop-up bucking -> reduction of the opening for the BB -> choke of the gun -> damage to the piston and gears. It depends on the chosen hop-up bucking, some fit better in the AirsoftPro hop chamber, others are tighter from the start and it takes little for the problem to occur. But in any case, solid fixing the barrel in the hop chamber is a necessity.

  • I have verified that the inner stainless steel barrel from SpecnaArms / ZCI has a cutout for the barrel lock that is too large and the blue plastic barrel lock in the JJ parts kit is too loose and unusable. Therefore, I printed my own, custom-fitted, from PETG. Print model attached. If even with it there is occasional narrowing of the opening in the bucking, it will be necessary to modify the lock model so that the inner barrel is extended out of the hop chamber even more (or grind down the outer side of the bucking lips, not tested).

• Barrel length

  • For maximum performance and precision read this article https://www.reddit.com/r/airsoft/comments/s41swi/cylinderbarrel_volume_and_bb_weight_ratio_guide/ and Best g36 right now?, topic about barell lenght

  • The original 509 mm barrel is therefore only suitable for very light BBs, according to the article on Reddit. See the table, for a full AEG cylinder:
    
    Cylinder Ratios
    BB weight-----Barrel Length-- Barrel Volume----- Ratio
    0.2g-----------435mm--------12423mm3-------2.17:1
    0.23g---------430mm--------12280mm3-------2.19:1
    0.25g---------425mm--------12137mm3--------2.22:1
    0.28g---------420mm--------11994mm3-------2.24:1
    0.30g---------415mm---------11851mm3-------2.27: 1
    0.32g---------400mm--------11423mm3-------2.36:1
    0.36g---------380mm--------10852mm3-------2.48:1
    0.40g---------355mm--------10138mm3-------2.65:1
    0.43g---------345mm--------9852mm3--------2.73:1
    0.45g---------335mm--------9567mm3--------2.81:1

  • With a full classic AEG cylinder, M130 spring and 0.32g BBs I took a specna arms 407 x 6.02 mm barrel. My gun has 2,4 J on that setup, with hop up on)

• Testing R-HOP Bucking (testing, I was curious if it has any advantages over 4UANTUM)

  • I personally struggled with this testing for a long time.

  • Specifically, I tested the r-hop patch from Snipetor for the ZCI barrel https://www.snipetor.com/product/zci-r-hop/ with a TNT silicone hop up bucking surface and a Prometheus blue hop up bucking surface. The barrel choked, even better fixation of the barrel in the hop chamber did not help, even choking the weapon destroyed the piston. Later I found out that these 2 hop rubber bands are not suitable for R-HOP at all, and in themselves cause a problem with choking, see the link. https://www.silentindustries.eu/product/drop-in-r-hop-for-prometheus-eg-barrels/.

  • So for now I have returned to 4UANTUM bucking, which is definitely less prone to choking the weapon. And I'm waiting for a suitable hop up bucking for R-HOP directly from Snipetor.

Tools

• Home workshop

• PLA+ or PETG filament, 3-4 perimeters, 40 - 60% Cubic infill

  • My printer settings were: PLA+ PM, nozzle 0.6, layer height 0.28, 3 perimeters, infill 30% + brick layer BETA 0.2.1. https://github.com/GeekDetour/BrickLayers (warning - heavy stringing), ORCA slicer, cut into 2 parts due to the maximum height limit of my printer (155 mm in Z axis). Weight of the mainbody v1.5.2 printout was approx. 100g.

  • I think the brick layer is not necessary for sufficient strength.

• 16 mm drill bit for cleaning the main hole

• Something for deburring

• Rounding

• Original 3x M3 screws

• 1x M3 or M3.5 screw for the front hole

• MAMUT TOTAL glue for fixing the outer cylinder in the printed part, for sure

• …

Instructions - not finished yet!

1. Move the battery back into the stock. Rewire the wiring if you haven't already. There will probably be no more room for the battery in the forend of the weapon. Untested.

2. Fix gearbox play in gun body?

3. Measure the original outer barrel mount and check the dimensions, especially the bolt spacing

4. Print TOOL 1 and test the dimensional accuracy of your printer. After cleaning it from burrs and stretching it with a 16 mm drill, it should fit snugly on the outer barrel. It is better to print a smaller hole and fine-tune it with several stretches with a drill.

5. Shorten one part of the outer barrel to a length of 212 mm (if you want the outer barrel to be about the same length as it was originally on the E2 version that I have. My gun had a 510 mm inner barrel and cca 515 mm outer barrel, now after the modification the outer barrel is still the same length, but I use a shorter inner barrel), remove burrs and sawdust!

6. Print TOOL 2 and mount the outer barrel in it, place it in the airsoft gun and visually test whether the gearbox nozzle comes out approximately in the middle of the outer barrel hole, in the x and y axes. Insert the outer barrel into the part until it stops, into the narrowing, and mark the position.

7. Visually check that the nozzle is centered in the outer barrel again

8. We will use the original metal mounting frame, but it needs to be modified. Cut off the nut that the barrel was screwed into and file the height of the protrusions so that they do not interfere with the 16 mm hole for the outer barrel - test the exact height with the printed part.

9. Print TOOL 3, insert the outer barrel into it, the distance from the edge measured in point 2, I got 2 mm. Tool 3 serves as a guide for the file, in the aluminum barrel you need to drill, grind 2 grooves so that the M3 screws pass through them. Use the file from the smaller diameter to the larger. The grooves should be horizontal, just wide and deep enough for the M3 screw. Check with a screw.

10. Print the main part for a final dimension test. 2 perimeters, 10% infill will be enough ... Remove the burrs and insert the shortened outer barrel, align the filed grooves in the barrel with the M3 holes on the sides, try to assemble the weapon, check that the nozzle still comes out in the middle of the outer barrel hole.

11. Visually check that the nozzle is centered in the outer barrel.

12. If everything is fine, print the part with the final recommended settings. Remove the burrs, check the dimensions, holes, try to assemble everything.

13. Visually check that the nozzle is centered in the outer barrel.

14. My nozzle was correct in elevation, but too far to the right when viewed from the gun towards the barrel. In addition, the front of the mechabox was too loose, moving sideways, especially to the right. This resulted in an occasional deflection of the path of the fired bullet to the right, about one out of every 3 to 5 bullets. So I needed to move the mechabox slightly to the left and at the same time fix it in that position, I am working on a solution right now.
    
    The fit of the mechabox in the body of the replica is not as good in the G36 as in the M4 replicas, this is a manifestation of this imperfection
     

15. …

The original solution of the manufacturer was:

The metal is a center plate of alloy or aluminum, rails through which 2 bolts and nuts pass to the outer barrel. Unfortunately, this is a poorly designed concept of barrel mounting on the G36, most cheap manufacturers.

• - The outer barrel starts far from the hop up chamber, unlike the M4

• - The outer barrel nut basically holds it like a cherry on a stick

• - the shape of the iron part has no lateral strength, the outer barrel and thus the inner barrel then flies from side to side

• -> inherent shooting inaccuracy of the G36 with this barrel attachment compared to the airsoft concept of the M4

It seems that other manufacturers (Ares, Specna Arms, S&T, NOVRITSCH, ...) have improved the barrel mounting system, for example by attaching a metal cap nut over the outer barrel. I recommend getting such a version of the G36 if you want to avoid this home modification for accuracy.