Try the buffer spring first and buy a buffer tube at the same time; both cheap. You may need to take some weight out of the buffer. I have a variety of uppers and a dedicated buffer spring and tube for the 300 BO. Good luck.
I have a 300 BO suppressed piston carbine built on quality parts. I have a POF base and shoot 3 other calibers. The suppressor will give you back pressure. For suppressed cycling I had to open up the gas port, remove the gas piston spring, lighten up the buffer spring, and remove the weights from the buffer itself. It has run flawlessly over several hundred rounds; make sure you run a good oil on the bolt. I wouldn't try to run subsonic rounds without a suppressor and expect the weapon to cycle properly. Good luck.