This project is currently in BETA (as of April 24)

Specifically, the longevity and durability of the PLA+ printed locking pin needs to be further tested.

UPDATE: A new experimental Reinforced Locking Pin has been added to the print profile. You can find it on its own print plate.

Check below for more info on how to make it and the materials needed.

If you run into any issues please comment below so I can use the data to find us a solution.

Adjustable Pistol Brace for your AR pattern, airsoft, short barrel, rifle, pistol, things.

Clone/replica of SB Tactical's very popular (and expensive) SBA3.

Parts Needed:

1x AR mag catch spring

1x M4x 30mm bolt screw

2x M4x 20-30mm bolt screw

3x M4 nuts

70 grams tpu

175 grams Impact resistant PLA (+, pro, or CF)

Optional/recommended:

1inch by ~2ft adjustable velcro strap

For reinforced locking pin:

1xM4x6mm Hex head bolt

JB Weld

Tools:

M4 screwdriver/Allen key

Drill gun with

-8mm or 5/16ths inch bit

Cost:

Filament $5

Spring $0.5ea ($12 for 20 on PSA)

Hardware <$1 ($15 for M4 variety box on Amazon)

Velcro Strap $13 on SB Tactical Website (or can buy 30 ft of adjustable strap on Amazon or $10)

Total: 

APB3 <$20 vs paying $125 for the SBA3

Assembly:

1. Remove all support material, note that there are two nubs on the back/bottom of the main body, do not accidentally remove these while trying to remove all of the support that surrounds them. 
2. Take two M4 nuts, and put them in the holes in the back and on the side of the main pla body. Rotate them until they sit into the holes and no longer rotate side to side, there will be room for them to move up and down, this is for if you want to upgrade to use thicker nylock nuts, so far nylock has been unnecessary.
3. Slide on the Tpu arm brace thing, it's easiest to gently rock back and forth till it pops over the nubs. – be careful as to not lose the nuts as you slide the tpu over them.
4. take your 2x m4 x20mm-30mm (do not use longer than 30mm as they will extend into the cavity and block buffer tube) and screw down the tpu brace
5. Drill out the hole for the locking pin using your 8mm or 5/16th inch drill bit, the goal is not to remove material but just make sure the hole is round and smooth from any bits or lingering supports.
6. Optional *Make the reinforced pin below*
7. Drop in the pin, hole end last, and push it down until you can see the pins hole through the slots in the main body. Slide the push lever onto the main body and slide a small screwdriver (any small cylinder) through the holes in the lever, main body, and the pin to the other side and through the M4 nut to make sure they are all lined up, leave it in. 
8. Take your remaining m4 bolt and start screwing it through the hole chasing the smaller screwdriver you used to line the holes up, go slow and check for bending/deformations that would indicate you are not properly lined up.
9. Lastly, insert your spring into the hole behind the pin. Use something (I used a flathead screwdriver) to push down the spring and then slide the spring tab over the spring until it pops into place. 

Making the reinforced locking pin

Materials needed:

Steel-reinforced JB Weld epoxy

1x M4x5-6mm Hex key socket head bolt**

**Please reference the photo for the specific dimensions needed for the bolt

Instructions:

1. Print your reinforced pin (not the same as the old pin) keep the orientation as in the print profile, and leave the supports off.
2. Mix your two-part epoxy well (you only need a little, maybe the size of 2 peas).
3. I recommend using some Q-tips as your applicators, cutting them in half, and using the stick end to apply epoxy and the cotton end to wipe up excess.
4. Add a drop of epoxy into the cavity in the top of the pin, use your q-tip to push it in, remove any air bubbles, and coat the walls. We don't want to FILL the cavity we just want to add a drop and coat the walls.
5. Thinly coat the threads of your M4x6mm pin, and slowly twist while sliding it into the top cavity, wipe up any excess that flows past the edge of the plastic.
6. You should have noted that there is a small hole connecting the cavity in the top, to the perpendicular hole where the lever will connect, ideally a small amount of epoxy found its way here, use your Q-tip and wipe away any excess that would block the lever pin later on.
7. IMPORTANT make sure the m4 bolt fully seats on the edge of the plastic, tolerances are tight, and if it is taller than it should be, you're going to have issues.
8. Also IMPORTANT once you've stuck it together and cleaned up the excess, LET IT CURE (bolt head down) for the whole amount your epoxy recommends, applying any force while curing, will compromise the cement's integrity. Just let it rest, do not continue assembly until it's fully cured.

Fin.

 Trouble Shooting:

• It has come to my attention that not all AR mag catch springs are the same spec. If you find your spring exceptionally difficult to install (it should still be a little difficult) then feel free to take some pliers or wire cutters and trim the spring a couple of mm until it is still 1-3 mm above where the spring tab would normally sit flush, make sure your lever is in the fully seated/locked position. You don't want to undershoot it.
• Note the push lever will be very tight at first, and it may seem like there is not enough spring force for the brace to lock into place on its own. However, after a little use, 3-5 min manually pushing the lever up and down the push lever will loosen up and reliably lock into place.
• If your stock locking mechanism is still giving you trouble -- the spring doesn't always push the pin up into the locked position, even after working it in for a couple of minutes and also making sure there is no support debris-- then you most likely have over-tightened the bolt that holds the lever/pin. Loosen it a ¼ turn at a time and you should notice the spring pushes the pin into a locked position much easier. If you are worried about the bolt falling/backing out, upgrade your nut to a nylock nut. If this doesn't work then you have a bad dimensional print or a poopy spring, idk.