https://greyhive.com/videos/watch/9af03fef-0d63-4759-ab58-3b40ebe4a7f9 All right. Let’s start this build. The footage was shot on F4 Defense receivers. I did the same work on the new Aero Precision M4E1 set, so ignore the receiver brand in the clips. Upper lineup: 17-inch Strike rail and its barrel nut (those get their own video), a foot-pound torque wrench with the proprietary nut wrench, an SLR Sentry adjustable gas block and nitrided gas tube, a 6.8 mm SureFire SFMB, an 18-inch 6.5 Grendel BSF barrel, a Geissele torsion bar, a level, lapping compound, and my lapping tool. G&G Rifle Works makes that tool to my design. New kits ship in a clear tube with packets of compound, so you do not have to source compound separately. You can chuck the tool in a drill or, with the extra mass in the head, lap by hand with the upper vertical and let gravity help. First I lap the upper. Compound goes under the head of the tool. Insert it and turn until the anodizing is gone from the face that meets the barrel extension. Hand lapping does not take long. I have a dedicated lapping video; the card should be in the corner. I wipe the tool and put it back in the tube for the next build. The BSF extension is a tight fit. I tap it in with a soft-face mallet. The Geissele torsion bar goes in the vise. The grooves lock into the barrel-extension lugs. Slide it on, align, and it seats. Thread the nut on by hand. With a torque adapter, keep the wrench axis 90 degrees to the adapter. In line with the wrench you will under-torque. Either side is fine as long as you tighten the correct direction. Season the threads: torque, loosen, repeat three or four times, then final torque. On this Strike nut, a valley must line up with the gas-tube hole. Before the last torque I back the nut off, expose the receiver threads, and apply anti-seize so a future barrel swap does not seize. Aeroshell is common; I use anti-seize. A few dabs on the threads, run the nut down, then final-torque so a valley lines up with the gas-tube port. Start at the low end of the spec; if it will not index, go toward the high end until it does. Confirm the gas tube will clear. Gas-block work is slower with one hand. I put the block in a small vise, start the roll pin so it stands, then use channel locks to start it so it cannot fall out. The gas tube goes in with the large hole down and the front side holes aligned with the pin. I flip the assembly, put one jaw on the detent spring leaf and one on the pin, and squeeze the pin through. The BSF barrel is already dimpled. An SLR dimple jig can add a second dimple if needed. I slide the block on, remove the set screws, align to the dimple, blue Loctite, and tighten both screws firmly. The Strike rail slides on. One bolt, blue Loctite, torque. I install the SureFire SFMB only with a crush washer for now—no timed shims or Rocksett—until I confirm the gun is gassed. Even with an adjustable block I want the brake removable if the block has to come off. Like the 6.5 Creedmoor build, I use a CTS Engineering active-recoil buffer, anti-tilt version. The front nub is meant to enter the back of the carrier and limit tilt. I did not know at first that a JP VMOS carrier’s rear hole is smaller than mil-spec, so it would not fit. G&G turned the nub down on a lathe until it did. The Grendel lower is built like the Creedmoor lower: JP Easy Trigger with the Armageddon Gear Revolution roller. That install is in the Creedmoor lower video. Mr. Mill and I took it to the range to set the gas and confirm ejection. I opened the gas a little. Next trip is groups. That is the build. Like, subscribe, Facebook, Patreon if you want to support it. See you next time. #6.5Grendel #RifleBuild #AR15 #BSFBarrel #AeroPrecision #UpperReceiver #Gunsmithing #GunTube Mon, 09 Nov 2026 16:58:55 GMT https://validator.w3.org/feed/docs/rss2.html PeerTube - https://greyhive.com https://greyhive.com/lazy-static/avatars/5746210d-885d-44b2-9be0-92bf1e4d34df.webp https://greyhive.com/videos/watch/9af03fef-0d63-4759-ab58-3b40ebe4a7f9 All rights reserved, unless otherwise specified in the terms specified at https://greyhive.com/about and potential licenses granted by each content's rightholder.