Breacher - metric hardware version

This is a modification of Breacher for metric hardware,  Also includes "exothermic" cosmetic modification from @Frutiger_3662133.

Hardware

• Main spring: OD 22mm, wire diameter 2mm, length ~140mm

• Plunger tube + magazine tube: ID 35mm, OD 38mm , length ~149mm + 330mm (original plunger tube is ~145mm long, but for me this turned iut to be a bit short - the tube didn't reach the ball detent with the priming grip pushed all the way forward).

• Small O-rings (x2): ID 15.6mm, thickness 1.78mm (same size as original, but in mm. These are pretty common).

• Larger O-rings (x2): ID 30mm, thickness 2.5mm.

• Plunger padding (see original BOM). Any similar sizes should work, also can be casted from 2-component silicone (mold files attached in stl_extra folder).

• Larger heat-set inserts (x4, for threaded rods): M4x8x6.

• Smaller heat-set inserts (x10 + 3): M3x6x5. 10 are required (PlungerCap needs only 3 +  3 optional for match saver.

• Nuts and washers:

  • DIN 6923 M4 flange nut (x2) - use for EjectionPort_Back, with flange pointing outwards. M4 nuts are smaller than 8-32 from original BOM, so we use the flange to increase surface area and reduce plastic stress.

  • DIN 934 M4 hex nut (x6).

  • Din 433 M4 slim washer (x6) - use with hex nuts.

• Threaded rods: M4, length 2x203mm + 2x305mm + 2x394mm.

• M6x20 dowel pins (x2): use instead of nylon spacers for trigger and sear.

• M3x10 self-tapping screws for plastic (x50? + 2). Countersunk head, flat tail. These are used instead of #4 small screws. +2 extra if you can't find shorter screws (M3x6).

• Extension spring: OD 6mm, wire thickness 0.6mm, length 25mm

• Smaller springs (x6): OD 4mm, wire thickness 0.4mm, length 15mm

• Larger springs (x4*): OD 6mm, wire thickness 0.6mm, length 15mm. See note below

• Weaker larger springs (x4*): OD 6mm, wire thickness 0.5mm, length 15mm. See note below

• Magazine tube springs - I couldn't find a compatible generic version, if you don;t live in US and cannot get FoamBlast springs, AK blaster Mod hasthese sold separately from the Breacher kit.

• Hardware from original BOM:

  • Ball detent 6x7mm

  • POM bearing 623 3*10*4mm (x4)

  • M3x12 socket head screw (x12)

  • M3x16 socket head screw (x7)

  • M3x20 socket head screw (x3)

  • M3x25 socket head screw (x5)

  • M3x30 socket head screw (x3+) - for match saver and other pic rail attachments

  • M3x50 socket head screw (x12)

Spring adjustment

I found that the larger springs on the extractor and the shell stop are too strong (although they have the same OD and thickness as in original BOM). The shells would sometimes get stuck in the magazine, and the extractor required too much force to latch onto the shells (I broke some shells and the boltface this way). Replacing these springs with weaker ones (with 0.5mm wire thickness) helped. I didn;t replace the spring below the sear, but I guess you may also use a weaker spring for it to avoid buying a pack of 0.6mm springs to use just one.

Unchanged parts (get STLs for these from the original model or import from the combined .step file)

• Picatinny rails

• Muzzle + threaded tube extensions (if needed)

• Mag follower

• PlungerCap

• Lifter

• Lifter roller (I used the version with bearings from @EnteFPV_2159792)

• Ejector

• Extractor

• PlungerHead_B

• PlungerRod

• Catch

• PlungerGuide

• StockButt

Exothermic mod for metric hardware

I really liked aesthetics of @Frutiger_3662133's remix, but I don't have any experience with Rhino 3D (and also had only a limited trial license for it), so I decided to try and recreate this mod for metric hardware in FreeCAD.

How to use

If you use Bambu Studio, you can just use the provided 3mf file.

If you use another slicer, import a .step file from the exothermic_parts folder. Each file contains 2 "parts" - the part itself and a set of secondary color slices. Select the slices "part" and change its type to modifier, then select another filament for this modifier.

Details

The scripts for generating the slices are in exo_scripts.zip. gen_arithmetic.py just generates boundaries for the slices (I used the algorithm from original Grasshopper script). make_slices.py, when imported in FreeCAD, generates the slices (there are some hardcoded part names, though).

Initially, I tried using intersections and cuts to split each part into 2 sets of slices, like in the original Exothermic mod, but there were some geometry errors. Some parts were ok, others didn't split nicely even after changing the number/position of slices and order of operations. But then I thought, why bother with intersections, if I just can export slices and use them as part modifier in the slicer? So, the script now generates only bounding boxes for slices, and the slicer does the rest.