Spectre's U-Bolt Bolt-Up AR-15 Lower Receiver, "The Firebolt" Original Design by RollTroll Modifications by Spectre Version 1.69 Description: As a big fan of bolt-together lowers and RollTroll's take on the idea, I decided to take what knowledge I had regarding the weaker points of both this particular lower and other lowers I've printed as well and combine the reinforcements into one revamped package. Every part of this print aside from the trigger guard has been revamped to accommodate thicker, stronger FCG walls with inset cutouts to allow for a precise fit of the hammer and the trigger, as well as the springs. The buffer tower has not only incorporated the UBolt into it's design, but has also been reinforced all-around with thicker arms (a key point of failure with my prints), a slightly shorter base to allow for easier buffer tube installation, and a very slight reduction to height to allow for easier charging handle movement. Another key point of failure with many other lowers is the front takedown pivot hole, which has not only been revamped to include more material on the front face, but also has more material on the perpendicular face at an angle, where the magwell walls become thicker towards the front of the lower. Caliber's Available: 5.56, 9mm, .45 ACP The 5.56 version also has a bolt catch assembly if you want to utilize it. NOTE: Print one (1) of each part depending on the caliber you choose. If you want to utilize the UBolt, swap out the necessary parts with the 4 corresponding labeled UBolt parts. All 3 calibers are compatible with the following 6 parts: -Buffer Tower -Grip Part -Side Left -Side Right -FCG Well Bottom -Trigger Guard The Pistol Grip is compatible with both the standard lower and the UBolt, but the UBolt Pistol Grip is not compatible with the standard lower. This includes both the standard buffer, the UBolt buffer, and the printable buffer tube. If you want to switch your lower's caliber, simply print the necessary 4 mag well parts for that caliber and swap. If you want to print the printable buffer tube, replace the buffer tower (and the grip if you use it) with the parts from the folder. Instructions: Hardware Requirements - UBolt (https://www.mcmaster.com/3201T49) - 1 x Ejector (FOR 9mm or .45 ONLY) (This can be machined or cut from metal if you have the resources to do so, the ejector file has been included for reference.) Example: https://www.newfrontierarmory.com/product/ejector-c9-c45/ - 1 x 1/4" x 1" Self-tapping sheet metal screw (for Grip) - 2 x 1/4" x 2" Pins w/ holes for either key rings or hairpins to lock in the takedown pins. All hardware M3 sized, minimum length required. AR-15 -Nut x18 -Trigger Guard and Grip Part - 10mm x 4 -Buffer Tower Arms - 12mm x 2 (DO NOT EXCEED 14mm OR THE HAMMER WILL INTERFERE) -Mag Well to Mag Well Rear - 35mm x 5 -Mag Well to Sides - 10mm x 3 -Grip Part - 25mm x 2 -Buffer Tower Bottom - 40mm x 1 -Buffer Tower Rear - 50mm x 1 AR-15 w/ Bolt Catch -Nut x18 -Trigger Guard and Grip Part - 10mm x 4 -Buffer Tower Arms - 12mm x 2 (DO NOT EXCEED 14mm OR THE HAMMER WILL INTERFERE) -Mag Well to Mag Well Rear - 35mm x 4 -Mag Well to Sides - 10mm x 3 -Mag Well Right to Mag Well Rear (Above Magazine Release button) - 14mm x 1 -Grip Part - 25mm x 2 -Buffer Tower Bottom - 40mm x 1 -Buffer Tower Rear - 50mm x 1 AR9 and AR45 -Nut x23 -Trigger Guard and Grip Part - 10mm x 4 -Buffer Tower Arms - 12mm x 2 (DO NOT EXCEED 14mm OR THE HAMMER WILL INTERFERE) -Mag Well - 35mm x 8 -Mag Well to Sides - 10mm x 3 -Grip Part - 25mm x 2 -Buffer Tower Bottom - 40mm x 1 -Buffer Tower Rear - 50mm x 1 -Ejector - 20mm x 2 Printing Settings: NOTE: These are just suggestions based on my experience with printed lowers. Print your parts however you see fit. -All parts should be printed at a 0.16 layer height. This will retain the most detail while not extending print times too much. -All parts should have 15-20 Top/Bottom layers, giving each part a 2.4 mm minimum top/bottom wall thickness. -All parts should use either the triangle or cubic infill pattern. Both have shown to be the strongest patterns via testing. -All parts should have a minimum of 25% infill. -All parts should have a minimum of 6 perimeters, e.g., 2.4 mm wall thickness with 0.4 mm nozzle. -The Buffer Tower should NOT be printed with outside walls first, this will cause the threads to fail. -Parts that should have higher perimeters and infill percentages are the Buffer Tower, the Grip Part, and the Mag Well Front and Rear. Everything else can be printed on the cheaper side. Printing Orientation: Buffer tower should be printed flat, perpendicular to the print bed, as if the stock were vertical (although you CAN print this part normal orientation for a stronger print, it will need supports.) Grip part should be printed on its side, safety pinhole down. Use tree supports if possible, touching buildplate. Mag well front should be printed on its side, with the pivot holes flat against the bed. Again, use trees but this time use the everywhere option so the entire flat face of the upper pivot hole is supported. Mag well back should be printed with the largest flat side against the print bed. This is the side opposite the mag well. Use tree supports with touching buildplate only. Both mag well sides should be printed on their largest flat face, the side opposite the mag well. Since this means the cutouts meant for the screws are printed open air, use regular supports. Use support blockers on the emblem if you print that version. No, the layer lines do not interfere with the magazine. Both left and right (rear) sides should be printed with the external walls against the print bed. This will allow for the FCG cutouts to be printed correctly. Fire control well bottom should be printed flat, so the side facing the trigger guard is against the print bed. Trigger guard can be printed either flat (so it looks like a bridge), or on its side (so it needs no support). Pre-Assembly: Here are some pointers to save you some headaches down the road: 1. Once the Mag Well Rear, Mag Well Right, and Side Right parts have all been printed, check to ensure that the Mag Release button fits through each part. Once that clears, mock assemble all of the parts together and see if the Mag Release button clears. Sand down parts as needed. 2. The Safety switch may not be able to fully rotate to "Safe" because of the position of one of the screws depending on the screws you purchase, however even with the amount its able to rotate, it will still function as a safety. (Test appropriately.) 3. I recommend lock washers for the Buffer Tower arm screws that feed into the fire control well to maintain a secure connection. Assembly: 1. Start with the buffer tower, sides, and grip part. Bolt together parts until the assembly is rigid. Install the buffer tube up until it is about to cover the buffer retention pin hole. Install the UBolt into the top of the buffer tower. (NOTE: you may have to drill out the UBolt holes with a .25" drill bit.) 2. Affix the plate to the bottom of the buffer tower and begin to feed the nuts onto each UBolt thread, taking note not to torque down one side more than the other. (NOTE: It is helpful to follow the Vanguard instructions UBolt installation at this point, included as "Vanguard README.") 3. Once the UBolt has been grinded down so that it is relatively flush with the top of the buffer tower, you may install the safety selector, grip, and safety selector pin and spring. Both the safety selector hole and pin hole for the safety selector might need to be drilled out a bit to allow for clean installation and movement. 4. The Grip should have no play in it once installed, so don't be afraid to wrench it down. 5. After the safety has been installed, install the Fire Control Well Bottom part, as once the Fire Control Group is installed, you will not be able to screw in the part. 6. Assemble the Mag Well Front and Sides together. 7. Install the Mag Well Rear part along with the Mag Well assembly, but do not fully feed the screws through. You will need the one of the sides to be flexible in order for the FCG to slide into position. 8. Install the FCG. You may have to drill out the pin holes using a 5/32" drill bit. Both the trigger and the hammer should pop into position once seated. Check to make sure that the spring legs on the hammer spring are seated in its cutouts as well. 9. Finish screwing in the 3 screws through the mag well rear. 10. Install the Trigger Guard. 11. Install the Mag Release. 12. Check the takedown pin holes for clearance, and if needed, drill out with .25" drill bit.