Spooky's U-Bolt Bolt-Up LR-308 / AR-10 Lower Receiver, "The Thunderbolt" Made by Spooky Version 1.420 Description: Just like the Firebolt, the Thunderbolt aims at being the strongest, most rigid 3D printed AR-10 frame available. Utilizing a bolt-up design as well as incorporation of the UBolt, the Thunderbolt gains its strength from a multitude of interlocking parts from the buffer tower all the way to the magazine well. This design uses the DPMS standard, meaning that some parts of an AR-15 lower parts kit are usable with this lower receiver. This receiver is NOT compatible with Armalite-style AR-10 upper receivers. Parts from an AR-15 Lower Receiver parts kit that are NOT compatible with a DPMS style lower include: -Bolt Catch -Bolt Catch Roll Pin (though I never had an issue) -Buffer (see https://308ar.com/ar-10-308-ar-compatibility-reference-guide/) -Buffer Spring (also see https://308ar.com/ar-10-308-ar-compatibility-reference-guide/) For more information on compatibility, see this guide: https://www.wingtactical.com/blog/what-parts-are-interchangeable-between-ar15-ar10/ Unlike the Firebolt, the Thunderbolt only comes in one version due to the needed strength to handle .308. This receiver also comes with a bolt catch, standard. NOTE: Print one (1) of each part. Instructions: Hardware Requirements - UBolt (https://www.mcmaster.com/3201T49) (cheaper: https://www.amazon.com/gp/product/B002Y0VRI8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1) - 1 x 1/4" x 1" Self-tapping sheet metal screw (for Grip if you do not want to use the standard grip screw.) - 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. Here's a set of M3 screws that contain all the necessary bolts: https://www.amazon.com/gp/product/B07L65DHV6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 AR-10 -Nut x21 -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 - 12mm x 1 -Grip Part - 25mm x 3 -Buffer Tower Arms to Sides - 40mm x 2 -Buffer Tower to Sides - 45mm x 1 (The bottom-left screw of the triangle of screws.) -Buffer Tower Rear - 50mm x 1 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 50% 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. Printing Orientation: Buffer tower should be printed flat, threads down 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 funkier 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 back. Mag well rear 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. 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 and cleanly. Sand out the cutout for the bolt catch. 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.