Welcome to THR.
Please give us a bit more information please.
Type of ammo used and more detailed information as to how gun is malfunctioning.
Two most often problems with shotguns not running : Chamber and Extraction. Does not matter if semi-auto, or another plaftform. Chamber is No. 1
Without knowing more, I'll toss some ideas out, forgive me if I touch on something you already checked -still it may assist another with a similar problem.
-I assume this has the new gas system, therefore one cannot assemble gas system incorrecty
-Pipe cleaned the ports, so no debris from clean and lube after getting intitial new gun cleaning
-Chamber is clean and dry
-Extractor is clean, dry. Make sure that grove in barrel extractor fits in, is lined up, and clean too.
-Shells used are what that gun is designed to run. Meaning, if the gun was designed to run 2 3/4 " , 2 3/4 dr equiv loads of 1 1/8 oz shot of 1200 fps, [Skeet Load] it May not run a 1oz or 7/8oz payload. "Some" tactical guns prefer a 3 dr equiv of 1 1/8 oz payload at 1200 [Trap Load] to run the gun
-Quality shells used. Some of these promo loads are not in spec, therefore hindering
chambering , and the rinky-dink metal used for base , being rinky dink and / or out of spec will not
extract. Some of these plastics are just poor quality, and break down faster causing plascization of chamber. Just a rough chamber.
Try a Federal Value Pack of 3 dr 1 1/8 oz laods, and get a box of Remington STS target loads.
Chamber cleaning . Wisps of 0000 (4aught) steel wool or finest grit of Scotchbrite pad around a nylon bore brush. Actually I prefer a 10ga brush for 12 ga chambers and mag tubes. Chuck the cleaning rod into a cordless drill- done.
Clean the barrel the same way with a 12 ga brush, use a pipe-cleaner to clean ports.
Leave choke tubes in protect threads always.
HTH
