Worn out carrier will let gas bleed off and not let it stay in the carrier and bolt to pressurize the system. Or a out of spec carrier will do it too. When I need to change bolts, I change the whole BCG. Could also be as simple as the carrier key not sealing as well as it should bleeding gas.
There are a lot more causes of a bcg not locking back than just buffer weight and springs. Heck, even the hammer springs play a roll in how the bcg works. If it is a new spring it holds just a hair longer as the bcg needs to overcome the spring rate the hammer has re cocking it. There is a lot of stuff that works all together as a system to make a ar run. Some things you can get away with and all it will do is wear out other parts. When you have multiple things out of spec you need to find out what it is and fix it. but you also need to know how things work first. And most people don't have a clue how things actually work other than what is regurgitated on most forums.
Bring another bcg with you next range trip and go from there. Then go to a standard weight carbine buffer. Not a H, H1,H2......
Also you need to pull the gas block and see what size of port it has. You will need a good set of pin gauges to do this. You should have at min 0.068" for carbine to be reliable. And 0.076" for a mid length gas.
