Father back in thread someone mentioned possibility of a burr as the gas port. Have built over 150 AR uppers and well over 70 complete ARs of which 1/3 of complete builds have been for myself and rest working for an 07 SOT. I chamber cast every personal barrel before assembly and inspect all barrels with a bore scope. Save the video plus still captures of every personal upper ever built. It is amazing how many barrels (especially under $300 tubes) will have a small burr or rough area where the gas port punches through the rifling. If building on a bargain barrel with such an issue (based on throat) if both throat and gas port are rough will run three and only three Tubbs fire lapping rounds down the tube then reinspect. Many barrels, especially 18" with rifle length gas, have to open ports and don't understand why done on my mill are always crisp but from factory can be rough. On all my hotrod ARs and bolt guns (204 Ruger, 22 Nosler, 6mm×6.8 etc in repeaters then 22-250 AI, 22 CHeetah and up through quarter bores, 7mm Practical and hot 30 calibers) keep my original chamber cast, recast every 1,000 rounds or less watching for pores to open up telling me it's time to lap throats. Same with the bore scope, can compare now to new and know if throat lapping to close open pores in steel is due.
Any rough surface whether throat, rifling or port is going to pick up lead from a non jacketed bullet and copper foul if using jackets. Knowing when and if to lap and how can almost double barrel life in some cartridges. A nice smooth bore is a friend to cast boolits. Someone mentioned using cast in 6.8 spc II. Have over a dozen 6.8s and they don't like subsonic or cast as much as would like though some are acceptable. Have 10.5", 16" and 20" 1:7 fast twist 6.8 barrels for shooting subs (gave up on 6.8 for subsonic same as 5.56 and use 458 SOCOM) as the 1:7 tubes shoot Cavity Back 200 grain bullets well at subsonic speed but not much else. Give me a 400 to 600 grain 458 SOCOM cast boolit at 1,050 fps and can thump about anything I need to including wild hogs vewy, vewy qwietwy...
Almost every cast boolit I shoot in rifles gets a gas check and being able to punch your own using scrap copper sheet or even aluminum soda cans is a money saver and gives that extra velocity to make everything work better. Commercial gas checks have gotten more expensive than I want to pay for a fully drawn jacket so I now punch my own in 224, 257, 308, 311/312 up into pistol sizes. I don't use aluminum unless know the alloy in nice barrels but most of us have a couple of factory OEM takeoffs or PSA bargain tubes we can abuse more. Spent a lot of time working on cast boolits in 308 during Sandy Hook and about the time began to see fruits of my efforts component bullets dropped so cheap again my time was worth more than making rifle bullets whether cast or swaged.
Have a die to draw 22 LR cases into 5.56 jackets and get a decent 60 grain bullet but is not great on game except varmints. Have a die to draw my 22 Mag cases into 6mm jackets and currently have a five gallon bucket set aside of 60 grain 5.56 soft points for emergency use which assume is soon. Have been stunned to see 5.56 M855 green tip ammo selling for $3 per round the past month with fair share of buyers. Unlike Sandy Hook my wife told me in March no selling ammo or projectiles like I did during Sandy Hook as she had a "bad feeling" would regret it and my wife's nose is better than most good bird dogs. Now looking at all the ammo/bags of projectiles/primers/powder in the locker and thinking 20 or 30 years of shooting left in my life and the 50% tax on all things ammo in HR 5717 am glad I listened to her. Even stocked up on components and equipment to reload rimfire. Instead of a hand press "multi-tool" for 22 LR and Mag now have real dies, shell holders, priming compound and multicavity molds for heeled 40 grain bullets.
Actually had worked on reloading primers during Sandy Hook as an experiment and got my formula with Berdan primers and cases to 95% reliability but then panic ended and quit. Will be revisiting that project as well as if able to get 98% reliability my steel ringing ammo may have to build/recycle from ground up. Suggest all get educated real fast on chemistry of priming compounds and some inventory just in case. If the government figures out they can't stop us from making what we need bans or taxes that hurt industries may be less likely. For flinging cast in 5.56 think smooth bore with no open pores or burrs, home punched gas checks and polymer coatings. Be as ingenious as possible and save some of your factory ammo for your kids or grandkids. What's leaving them a rifle they can't feed in the future?