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  1. # Modular Bullpup Automatic Rifle (MBAR)
  2.  
  3. The MBAR is a self-loading service rifle, with modular components allowing it to be upgraded over time.
  4. Unlike existing bullpup rifles, the MBAR was designed with modern ergonomics in mind:
  5. all controls are ambidexterous and mirrored, uses the same manual of arms as the AR platform familiar to most people,
  6. and ejects casings downwards.
  7.  
  8. Costs are kept low by using as many off the shelf components as possible, notably using standard AR pattern bolts and
  9. barrels.
  10. This allows users to take advantage of existing barrels in various calibers with no modifications to the weapon,
  11. and allows national militaries to continue using existing logistics.
  12. Furthermore, this rifle was designed with modern manufacturing methods in mind, many of the parts can be 3d printed.
  13.  
  14. The modular components of the rifle are the magwell, fire control group, ejection port accessory, and handguard.
  15. These components will be open sourced, and specs will be published to encourage development and production of
  16. aftermarket accessories.
  17.  
  18. The design incorporates all features that are expected of all modern fighting rifles:
  19. adjustable short stroke gas piston, free float handguard, a light/crisp trigger, and picatinny/MLOK accessory slots,
  20. with the goal of becoming the first bullpup rifle meeting the standards necessary for viable for widespread adoption as
  21. a service rifle.
  22.  
  23. ## Renders
  24.  
  25. ### Exploded View
  26.  
  27. ![Exploded View](RENDERS/exploded_view.png)
  28.  
  29. ### Side
  30.  
  31. ![Side](RENDERS/side.png)
  32.  
  33. ### Brass Catcher
  34.  
  35. ![Brass Catcher](RENDERS/side_with_brass_catcher.png)
  36.  
  37. ### Rear
  38.  
  39. ![Rear](RENDERS/rear.png)
  40.  
  41. ### Top
  42.  
  43. ![Top](RENDERS/top.png)
  44.  
  45. ### Gas Block
  46.  
  47. ![Gas Block](RENDERS/gas_block.png)
  48.  
  49. ### Ejection Port
  50.  
  51. ![Ejection Port](RENDERS/ejection_port.png)
  52.  
  53. ### Magwell
  54.  
  55. ![Magwell](RENDERS/magwell2.png)
  56.  
  57. ### Bolt carrier
  58.  
  59. ![Bolt carrier](RENDERS/bolt_carrier_right.png)
  60.  
  61. ## Setup
  62.  
  63. You will want to install OpenSCAD (use nightly until there is a more recent release), FreeCAD, Intellij, and whatever
  64. slicer for your 3d printer.
  65. It is recommended to Intellij with the OpenSCAD plugin, but use OpenSCAD to render. Rendering with the Intellij plugin
  66. is slower. Make sure to use OpenSCAD with the manifold or fast_csg settings turned on, otherwise rendering will be
  67. extremely slow.
  68.  
  69. The SCAD folder contains all the code used to generate models, and edits should be done here.
  70. It is recommended to use those to make changes since dimensions are parameterized and comments provide context on
  71. geometry. Within the SCAD folder the assembly directory is used for generating images, and testing the fitment of parts.
  72. The util folder contains the `constants.scad` file that stores global variables, and modules (functions) that are used
  73. throughout.
  74. The rest of the folders are organized hierarchically.
  75. All units are in millimeters.
  76.  
  77. STL files are generated directly from OpenSCAD, and this is the format used primarily for 3d printing.
  78. Since the STL file format is just a bunch of surface triangles, it is unsuitable for CNC.
  79. For CNC you will need to generate STEP files, do not attempt to convert STL to STEP files.
  80. Instructions to generate the STEP files is below.
  81.  
  82. For each pull request, changes to any SCAD file(s) should include the corresponding changes to its STL and STEP file.
  83.  
  84. ### Generating STEP files
  85.  
  86. 1. Open FreeCAD
  87. 2. Click `Edit` -> `Preferences`
  88. 3. Click the `Workbenches` tab
  89. 4. Find `OpenSCAD` and click `Load`
  90. 5. Click OK and exit out of the settings dialog.
  91. 6. Click `File` -> `Open` and select a `*.scad` file. Do NOT import an STL file.
  92. 7. Select the top level geometry on the combo view, usually it will be a `union` or `difference`, and the last item in
  93. the list.
  94. 8. Click `File` -> `Export`
  95. 9. Save it as a file in the `STEP` folder, in the following dialog make sure units are exported as `mm` and
  96. international standard is used.
  97.  
  98. ## Off the shelf parts needed to purchase
  99.  
  100. | Part | Quantity | Info |
  101. |--------------------------------------------------|----------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
  102. | 4mm x 0.7mm x 10mm star drive flat head screw | 12-14 | 8 for barrel block, 2 for hand guard, 2 for trigger housing, 2 optional for connecting to halves of lower receiver if 3d printer is too small |
  103. | M2 x 10mm roll pin | 8 | 1 for magazine catch, 1 for bolt catch button, 2 for safety selector, 1 for charging handle latch, 1 for recoil spring guide rod, 2 for trigger module |
  104. | 1/4" x 28 screw | 1 | screw for grip |
  105. | AR-15 pattern pistol grip | 1 | for grip |
  106. | PC031-266-5000-SST-0599-CG-N-IN | 1 | striker spring |
  107. | safety plunger spring from glock upper parts kit | 11-12 | 1 for the safety block in the bcg, 2 for safety detent, 1 for magazine release, 1 for bolt catch, 2 for charging handle latch, 3 for trigger module, 1 for safety linkage, 1 optionally for trigger linkage |
  108. | magazine release spring from Glock | 2 | one each for magazine and bolt catch forward control linkages |
  109. | Bolt | 1 | either an AR-15 or DPMS pattern bolt of any caliber |
  110. | Bolt cam pin | 1 | either an AR-15 or DPMS pattern bolt cam pin |
  111. | Barrel | 1 | either an AR-15 or DPMS pattern bolt of any caliber |
  112. | AR-15 trigger pin | 2 | used to pin gas block to barrel |
  113. | PC035-313-38000-177-4835-C-N-IN | 1 | compression spring for piston rod |
  114. | PC040-500-18500-SST-3840-CG-N-IN | 4 | compression spring used for recoil spring, could not find one at the 350-400mm free length so used 4 in series, for parts count purposes this will be treated as 1 part, consider making a custom spring for this in the future |
  115. | Ball Plunger M4x0.50 Thread Size | 1 | used for gas regulator detent in gas block |
  116. | M-Lok QD Mount | 2 | used in the lower receiver since plastic isn't strong enough for it |
  117.  
  118. **For the pistol grip, I would recommend a more vertical grip to give the magazine more space. This can be in issue with
  119. rock in magazines like AK pattern M14 or FAL magazines.**
  120.  
  121. ## Main parts to be fabricated
  122.  
  123. | Part | Material | Variants |
  124. |-------------------------------|-------------------------|--------------------------------------------------------|
  125. | Upper receiver | 7075 aluminum | No |
  126. | Upper plate | aluminum or polymer | No |
  127. | Hand guard | aluminum | Yes. There is a longer hand guard for extra rail space |
  128. | Charging handle body | aluminum or polymer | No |
  129. | Charging handle | aluminum | No |
  130. | Latch | tool steel | No |
  131. | Barrel block | steel | AR-15/DPMS |
  132. | Barrel nut | steel | AR-15/DPMS |
  133. | BCG | S7 steel DLC coat | AR-15/DPMS |
  134. | Striker | S7 steel chrome plating | AR-15/DPMS |
  135. | Safety block | steel | No |
  136. | BCG rear plate | steel | No |
  137. | Lower receiver | aluminum or polymer | No |
  138. | Stock plate | aluminum | No |
  139. | Take down Pin | aluminum or polymer | No |
  140. | Mag well | aluminum or polymer | AR-15/DPMS |
  141. | Bolt catch | S7 steel | No |
  142. | Bolt catch rod | aluminum or polymer | AR-15/DPMS |
  143. | Rear bolt catch button | aluminum or polymer | AR-15/DPMS |
  144. | Mag release | steel | AR-15/DPMS |
  145. | Mag release rod | aluminum or polymer | AR-15/DPMS |
  146. | Bolt catch button left | aluminum or polymer | No |
  147. | Bolt catch button right | aluminum or polymer | No |
  148. | Bolt catch forward linkage | aluminum or polymer | No |
  149. | Mag release button | aluminum or polymer | No |
  150. | Mag release forward linkage | aluminum or polymer | No |
  151. | Trigger | aluminum or polymer | No |
  152. | Trigger rear | aluminum or polymer | No |
  153. | Safety link | aluminum or polymer | No |
  154. | Trigger link | aluminum or polymer | No |
  155. | Safety selector left | aluminum or polymer | No |
  156. | Safety selector right | aluminum or polymer | No |
  157. | Safety detent | aluminum or polymer | No |
  158. | Safety bar | aluminum or polymer | No |
  159. | Gas block | steel | Yes, depends on shelf of barrel |
  160. | Piston rod | steel | Yes, different lengths for various gas system length |
  161. | Piston rod washer | polymer | No |
  162. | Gas regulator | steel | No |
  163. | Disconnector | tool steel | No |
  164. | Disconnector guide | tool steel | No |
  165. | Striker sear | tool steel | No |
  166. | Trigger module housing | aluminum or polymer | No |
  167. | Recoil spring guide rod rear | steel | No |
  168. | Recoil spring guide rod front | steel | No |
  169. | Recoil spring guide rod cap | steel | No |
  170.  
  171. **AR-15/DPMS variants means there is a version for each.
  172. For example if manufacturing a rifle for 556 NATO or 300BLK use the AR-15 size, if 762 NATO or 6.5CM use DPMS size.**
  173.  
  174. ## Accessory off the shelf parts needed to purchase
  175.  
  176. | Part | Quantity | Info |
  177. |--------------------------------------------------|----------|---------------------------------------------------------|
  178. | 4mm x 0.7mm x 10mm star drive flat head screw | 4 | 4 for optional cheek riser |
  179. | Ball Plunger M3x0.50 Thread Size | 2 | used in dust cover assembly |
  180. | safety plunger spring from glock upper parts kit | 2 | used in dust cover assembly, and adjustable cheek riser |
  181. | M2 x 10mm roll pin | 7 | used in dust cover assembly |
  182. | PT018-160-10750-SST-LH-0500-N-IN | 2 | used in dust cover assembly |
  183.  
  184. **The torsion spring that is used in the left dust cover needs to have one of its legs shortened (I used wire cutters).
  185. This is because the dust cover rod that is used to automatically open the dust cover lips is on the left side,
  186. and the excess length of the torsion spring leg that goes near it causes it to jam.**
  187.  
  188. ## Accessory parts to be fabricated
  189.  
  190. | Part | Material | Variants |
  191. |-------------------------------|----------|----------|
  192. | Fixed cheek riser | polymer | No |
  193. | Adjustable cheek riser base | polymer | No |
  194. | Adjustable cheek riser | polymer | No |
  195. | Adjustable cheek riser button | polymer | No |
  196. | Brass catcher | polymer | No |
  197. | Dust cover housing | polymer | No |
  198. | Dust cover | polymer | No |
  199. | Dust cover bar | polymer | No |
  200.  
  201. ## Manufacturing Guidelines
  202.  
  203. For 3d printed parts, a carbon fiber infused filament or nylon is recommended.
  204. For the components that are close to the barrel and bolt polycarbonate is another great option since it is the most
  205. heat-resistant polymer.
  206. I used PLA Pro for the external components that needed to be FDE in color.
  207. Print all parts with 100% infill and rectlinear infill pattern for maximum strength.
  208. For parts smaller parts in the lower receiver make sure to use 0.08mm layer height for higher resolution geometry.
  209. Don't forget to file away some of the support material on overhangs that stays behind, otherwise you will have issues
  210. with tolerances.
  211. Depending on the accuracy of your printer, you may need to file things down anyway.
  212.  
  213. For the upper receiver and handguard it is strongly recommended to CNC from a billet,
  214. otherwise most of the material is wasted if machining from a block of metal.
  215.  
  216. I used roll pins as bearings for several hinges, to reduce the friction of the bearing I crimped down the roll pins with
  217. a vise.
  218. Be careful to not crimp them down too much otherwise they could fall out.
  219.  
  220. ## Total Minimum Parts Count
  221.  
  222. | Category | Total | % |
  223. |----------------------------------------|-------|-----|
  224. | Purchased off the shelf | 46 | 50 |
  225. | Polymer (3d print or injection molded) | 24 | 26 |
  226. | Metal only (CNC or cast) | 22 | 24 |
  227. | Total | 92 | 100 |
  228.  
  229. ## Spring Specs
  230.  
  231. I purchased off the shelf springs from thespringstore.com.
  232. If you are unable to acquire those springs I have pasted the specs here, so you can find similar springs.
  233. Avoid music wire springs, they have poor corrosion resistance. Use stainless steel.
  234.  
  235. ### PC031-266-5000-SST-0599-CG-N-IN
  236.  
  237. | Measurement | Value | Tolerance |
  238. |----------------|---------------------|--------------|
  239. | Outer Diameter | 6.756 mm | +/- 0.008 |
  240. | Inner Diameter | 5.182 mm | +/- 0.005 |
  241. | Free Length | 15.215 mm | +/- 0.025 |
  242. | Spring Rate | 5.16600 N/mm | +/- 0.1 |
  243. | Max Deflection | 4.8030 mm | +/- 0.1 |
  244. | Maximum Load | 24.8200 N | +/- 0.1 |
  245. | Wire Diameter | 0.787 mm | +/- 0.0006 |
  246. | Solid Height | 3.937 mm | +/- 0.07 |
  247. | Total Coils | 5.000 | +/- 1/4 Coil |
  248. | Material Type | Stainless Steel 302 |
  249. | End Type | CG |
  250. | Wind Direction | Right Hand (RH) |
  251. | Finish | None |
  252.  
  253. ### PC035-313-38000-177-4835-C-N-IN
  254.  
  255. | Measurement | Value | Tolerance |
  256. |----------------|----------------------|--------------|
  257. | Outer Diameter | 7.950 mm | +/- 0.008 |
  258. | Inner Diameter | 6.172 mm | +/- 0.005 |
  259. | Free Length | 122.809 mm | +/- 0.2 |
  260. | Spring Rate | 0.46600 N/mm | +/- 0.1 |
  261. | Max Deflection | 65.2980 mm | +/- 0.1 |
  262. | Maximum Load | 30.4410 N | +/- 0.1 |
  263. | Wire Diameter | 0.889 mm | +/- 0.0006 |
  264. | Solid Height | 34.671 mm | +/- 0.07 |
  265. | Total Coils | 38.000 | +/- 1/4 Coil |
  266. | Material Type | Stainless Steel 17-7 | |
  267. | End Type | C | |
  268. | Wind Direction | Right Hand (RH) | |
  269. | Finish | None | |
  270.  
  271. ### PC040-500-18500-SST-3840-CG-N-IN
  272.  
  273. | Measurement | Value | Tolerance |
  274. |----------------|---------------------|--------------|
  275. | Outer Diameter | 12.700 mm | +/- 0.008 |
  276. | Inner Diameter | 10.668 mm | +/- 0.008 |
  277. | Free Length | 97.536 mm | +/- 0.1 |
  278. | Spring Rate | 0.34700 N/mm | +/- 0.1 |
  279. | Max Deflection | 78.7400 mm | +/- 0.1 |
  280. | Maximum Load | 27.3370 N | +/- 0.1 |
  281. | Wire Diameter | 1.016 mm | +/- 0.0006 |
  282. | Solid Height | 18.796 mm | +/- 0.07 |
  283. | Total Coils | 18.500 | +/- 1/4 Coil |
  284. | Material Type | Stainless Steel 302 |
  285. | End Type | CG |
  286. | Wind Direction | Right Hand (RH) |
  287. | Finish | None |
  288.  
  289. ### PT018-160-10750-SST-LH-0500-N-IN
  290.  
  291. | Measurement | Value | Tolerance |
  292. |-------------------------------|---------------------|--------------|
  293. | Outer Diameter | 4.064 mm | +/- 0.005 |
  294. | Inner Diameter | 3.150 mm | +/- 0.005 |
  295. | Free Position 270.000 degrees |
  296. | Spring Rate | 0.05100 N-mm/deg | +/- 0.1 |
  297. | Max Deflection | 252.7130 degrees | +/- 0.1 |
  298. | Max. Torque | 0.5080 N | +/- 0.1 |
  299. | Wire Diameter | 0.457 mm | +/- 0.0005 |
  300. | Total Coils | 10.750 | +/- 1/8 Coil |
  301. | Material Type | Stainless Steel 302 |
  302. | Wind Direction | Left Hand (LH) |
  303. | Leg Length | 12.700 mm | +/- 0.04 |
  304. | Finish | None |
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