FTN4 is the best printed suppressor out there. There are options for 22lr, 556, 308, 9mm, and 45. They need reinforcement, either an aluminum tube or a carbon fiber sleeve. With suppressors tax dropping next year, someone may come up with a better design eventually. However, the FTN series of suppressors is quite robust and can handle FA rates of fire, especially when it's made of PA6-CF or even better, PPA-CF.

More truly DIY designs that use non gun parts. This future-proofs against tyrannical legislation. As mentioned by an earlier poster, hybrid designs with a bit of metal work/reinforcing for longevity. I still think truly DIY designs in 9mm and 5.56mm are the holy grail, to go with 12g and 22lr. The most common, accessible calibres in other words.

The bolt has to weigh a lot more for those other calibers in a direct blowback firearm. In 9mm the bolt weighs about 1.7lbs. For 45acp and 10mm the bolt would need to be 2.3 and 2.8lbs respectively. It can be done but would require a lot of work to change calibers.

Edit: Source: https://10mmautocombat.wordpress.com/blowback-bolt-calculations/