Upgraded baffle stack more suitable to a low pressure, large volume can.
Prob the biggest issue with the original square section baffle stack is that high pressure gas can travel all the way forward between the tube and the baffle stack and then re-enter the stack and vent out the front without much interference.
A stack of individual full diameter baffles works better. There are also certain kinds of baffles that are more efficient with a large volume, low pressure system. I did a 9mm subgun can that metered around 121 dB which is roughly 10 dB quieter than the original MP5SD. At that level the thing is stupid quiet and all you really hear is the clack-clack of the action and then the thud of the bullet hitting.