I temporarily put each 16" barrel back on its upper, the stainless steel carbine barrel on the Colt upper it's been on for many years, and 12.7 Brownells barrel back on it's upper, which is a NDS forging. Am I the only one who thinks NoDak Spud sounds like the name of a cheap potato cannon, and not a real gun? "I just bought a NoDak Spud gun on TEMU. I like it better than the old Zamak Spud gun"
These barrels will be swapping uppers very soon, so the Colt lower with a carbine stock will be dedicated to the 12.7 barrel, and eventually the Dead Foot Arms Modified Cycle System (MCS) with GEN 2 Folding Adaptor. I bought the Right Side Folding adaptor so I can sling the rifle close to my chest with the stock folded, and flip it out at will. The 16" carbine barrel, 20" rifle barrel, and Can Cannon uppers will all interchange without an adaptor pin on the DPMS lower with an A2 stock. It's been awhile since I had the 16' barrel and full-length stock together, but that's what I used for years before I bought another lower with an M4 carbine stock.
I put a 1/4" bolt through the lugs on both lowers to line them up and looked at the muzzles. Despite what it looks like in the picture, the 12.7" barrel is shorter than the 16" barrel by less than the thickness of one cent. I figured that out when I held them together and stood them on their muzzles. They aren't
exactly the same length, but nearly identical. Good enough for government work, and good enough for me.
I used to have an M2037 Flare Gun that looked like an M203 Grenade Launcher mounted on the 16" barrel. I had a regular M203 mounting bracket for 20" rifles, but didn't have the fiberglass insulator/spacers to go with it. So I wrapped some foil-backed sound deadener I got at work around the barrel. It's like butyl rubber or something gummy and sticky. It's self-adhesive and comes in sheets. I put it on 1 or 2 layers thick, then I folded over the end of the mounting yoke to shorten it about 1/4" and slipped it over the sound deadener. When I took the flare gun off it left behind a sticky mess that I scraped off and painted over with cheap spray paint. I just used Goo Gone and a brass brush to scrub the remainder of the mess off, and sanded off the gloss black paint with old 120 grit sandpaper. When a sheet of sandpaper on my 1/4 sheet sander is worn out and has holes in it, It still has life left for hand sanding stuff like this.
I pegged the handguard cap upside down with a scrap of wood so I wouldn't blow paint into the gas tube hole in the front sight assembly. And I taped the slip ring back out of the way so I could prep the barrel for painting. I put about 5 coats of Rust-Oleum high heat BBQ black enamel on, letting it dry just a minute between coats while I shook the can. In a little while, I'll tape the slip ring to the front sight to keep it out of my way, swab the rear of the barrel with denatured alcohol again, and finish painting the rest of the barrel. Then I might mask off the barrel and paint the slip rig. I scratched it up pretty badly putting the Magpul MOE SL hand guard on the first couple of times. After it dies for 24 hours, it will be ready to go on its new upper. I could blacken the aluminum slip ring but flat black paint will look better than the glossy black finish it has.
BTW, NoDak Spud makes AR-180 type lowers that use AR-15 parts. It has imitation spot welds at the rear that make it look more like an authentic sheet steel lower.