Hanuman AR-15 Based Bullpup Receiver

This is the Hanuman, an AR-15 Based Bullpup. This file set is meant as a proof of concept. It is a prototype. There is no safety. There is no guarantee it will not harm or kill its operator. There is no guarantee it is legal in your location in all configurations. OAL Guidelines are stated with Federal Law in mine for the USA. Check for Local Laws before printing ANY firearm.

This design REQUIRES a bufferless AR-15 upper. Suitable platforms are the ARAK-21, Rock River Arms PDS Carbine, and CMMG Style .22LR Conversions for regular Upper Receivers. Use of 5.56/.223 with a standard BCG WILL result in catastrophic failure of the firearm, which could result in serious or fatal injury. I say again, DO NOT USE A STANDARD BCG IN THIS FIREARM.

Included in this design is a simple (optional but recommended) charge handle designed by patrickiv and RollaTroll. It is a single printed piece that slides along the Picatinny rail on top of the upper receiver. The concept is to give a standard AR a method of charging that is closer to the off hand while reloading or clearing a malfunction. When it is pulled back, one of the feet at the back actuates the catch on the rifle's original charging handle.  This charge handle design was initial created for the Hanuman Bullpup AR Lower Receiver but can be used other rails (resp.). The charge handle will work without issue on any upper with a picatinny rail, and should work with any charging handle. Optics interference will require forward mounting of a red dot sight or long eye relief scope.

OAL, the NFA, and YOU
If you are using an upper receiver with a 16" barrel, you must use the 3 Inch Buttpad Extension to meet the minimum legal OAL of 26". With a 16" barrel, the OAL of the platform is 26.25". If you are using an 18" barrel, you must use at least the 1" Buttpad Extension, bringing the OAL to 26.25". If you are using a 20" barrel, you may use the 1/4" buttpad extension without fear of breaking laws concerning SBR minimum overall lengths.

Printing Instructions
USE ABS PLASTIC.

All parts are oriented in optimum direction as far as I can determine, but it is left up to the experience and intuition of the print operator to decide. Support material is recommended to be on. Use settings that minimize warp and shrink, as well as maximizing accuracy and strength. Dimensions are CRITICAL.

Support material is necessary for Receiver_Grip_2, Receiver_FCG_Right, Receiver_FCG_Left, Trigger_Carrier, and Mag_Release_Arm.

Total weight of 12x receiver marked parts is 1.45 pounds, not including support material or auxilary parts.

Printed Part List
Print one of each file EXCEPT THE FOLLOWING.

• 1x Buttpad_Extension of the proper length to make OAL 26" or greater.
• 2x Trigger_Plate_Cover_Left
• 2x Trigger_Plate_Cover_Right

ASSEMBLY

1. Use Receier_Parts.jpg to determine alignment of the 12 receiver parts. They are seperated into four distinct sections. Forward (3 Parts), Grip (3 Parts), Magwell (4 Parts), and FCG (2 Parts). Using a suitable ABS Cement, cement the four sections together, taking care to make the interfacing faces absolutely paralell. Reference Receiver_Assembled.jpg for what the final product should look like.
2. Once glue is cured and straightness of iterfacing flats is assured, cement the four sections together as per Receiver_Assembled.jpg.
3. GENTLY Sand down a SLIGHT bit in the center of the four pins to allow for movement of Trigger, Mag Release and Lifter. They have been deliberately left without tollerance for their holes or hinges to allow for different printer tollerances. All printed pins except the Takedown_Pin are 6mm diameter and may be replaced with a suitable wood, plastic, or metal alternative. This is left to the Printer to decide.
4. Place trigger in center opening of Trigger carrier and place Trigger carrier pin through rear side hole, ensuring pin passes through slot of trigger. Place Trigger Carrier assembly through the top hole in the Grip_2 section of the receiver and then slide forward so that two rods on front of trigger carrier assembly engage the two holes in the front of the opening in the receiver.
5. Place Trigger Hinge pin through hole above trigger face, passing through center hole of Trigger.
6. Trigger should swing without resistance, moving Trigger carrier back and forth. If it does not swing freely, press trigger hinge pin out of receiver, and gently sand down the centers of the Trigger Hinge Pin before reassembly.
7. Slide Lifter into rectangular hole in rear of FCG section, aligning the hole in the lifter with the hole above the slot with the triangular nose forward, flat face upwards and pin into place with Lifter_Pin. Check for free movement of lifter. If lifter does not swing with very little resistance or freely, press Lifter_Pin out and gently sand center until it does.
8. Press Trigger_Rod_Right's two forward pins through the corresponding two holes in the Trigger carrier until the shaft of the Trigger rod rides flush in the trigger rod channel of the receiver, with the rear pin of the Rod entering the slot at the rear of the receiver, with the pin resting on the round bottom of the Lifter. Check for free movement. Gently sand upper and lower surfaces of the trigger channel on receiver if there is any binding.
9. Press Trigger_Rod_Left onto left side of receiver, matching the holes in the rod to the pins of Trigger_Rod_Right. Check for free movement and sand channel until free movement possible.
10. Install AR-15 FCG and check function. Do NOT allow hammer to fall at full strength onto the plastic receiver. Damage or breakage will occur. If you have checked the free movement of the printed trigger parts, the lifter will trip the trigger tail of the AR-15 FCG, resulting in the hammer falling, and the trigger return spring should press the printed parts forward enough to allow reset and refiring.
11. If the trigger does not return, remove Trigger_Rod_Right and Trigger_Rod_Left as well as trigger hinge pin. Place the spring from a click pen into one of the holes in the front of the forward trigger hole. This will place positive pressure on the trigger carrier, allowing the trigger to return, but will increase the pull weight of the forward trigger. Experiment with the spring length until trigger is as light as possible, with positive return.
12. Install Bolt Hold Open from AR-15 LPK if desired.
13. Place shaft of Mag_Release_Arm into hole at the bottom of the triangular receptacle on left side of receiver above grip. Slotted tab slides in at top dead center and then is rotated counter clockwise to captive position.
14. Place stud on Mag_Release_Bar into slot of slotted tab of Mag_Release Arm and press flush into Mag Release Arm Channel on receiver. Using thumb, check for free movement of Mag_Release_Arm and Mag_Release Bar. Sand Channel or shaft until freedom of movement is established.
15. Press Mag_Release_Right onto Indexed Shaft of Mag_Release_Arm and press until end of shaft is flush with surface of Mag_Release_Right. Check for free movement.
16. Place Mag Release Spring included with AR-15 LPK into hole just behind Mag Release Slot on left side of receiver.
17. Pressing down on the rear arm of Mag_Release, compress spring until Mag_Catch_Pin can be inserted through upper ear, down through hole of Mag_Release and seated in bottom ear of the Mag Release ears.
18. Check function of Mag Release by pressing forward on Mag Release Thumb Pad, rotating it counter clockwise until Mag_Release raises far enough to disengage a magazine
19. When all functions have been checked, Place Mag_Release_Cover into appropriate holes on left side of receiver above Mag Release Thumb Pad.
20. Press Trigger_Plate_Cover_Left onto appropriate holes at front and rear of receiver until flush and ensuring they do not interfere with operation. Do same with Trigger_Plate_Cover_Right.
21. Press your chosen buttpad extension onto rear of receiver to complete firearm.

END NOTES

These instructions assume you are not a moron. If something feels wrong, stop. If you have doubts, stop. If you get a funny tickle, stop. You can contact me via www.fosscad.org and then click on the Chat link at the top. If I am not there, another FOSSCAD member will be able to assist you or take a message and I will get back to you. This firearm is INCREDIBLY experimental, and is meant as an ergonomics, feasibility, and design test. You are taking a risk just by building it. If this bothers you in the slightest, do not build one.

If you've made it this far, I applaud you. You're one of the few that will actually succeed in creating this firearm. Feel free to modify, remix, create and destroy this model to your heart's content. We at FOSSCAD love pictures and testing videos, and even love having new names in the chat to talk to.

As always my friends,

You are free. Act like it!