Hello all. I am building a 300blk SBR with a 10.5 Hbar barrel. I plan on running a suppressor and will 90% of the time use subsonic ammo. I am looking at parts for the piston system and I was planning on a normal gas system. I friend at work tells me that a piston system is so much better, etc...

Is he right? If so, then what do I need for this build? And where do I get it? Keep in mind, I only know of the gas system and only researched it. I also want to use a nickel boron BCG. Can I still use it? Thanks everyone.

Having both in ,300 and building both, the best advice I can give is, become familiar with both systems. Neither is beter than the other, both have their place and is matter of opinion.
If your buddy has exp with both and can give solid proof of his exp including success and failures, so be it. But, just because someone read that a poston system is superior on the internet is no reason to build it.
Just find all the info you can on each and make solid decision based on your comfort level.
The best of luck.

I've never heard of a reliable .300 blk piston

Since you want such a specific set-up in something I have rarely seen done on a piston rifle, I wouldn't chance it.
Just go with the standard gas tube set-up.

In 300 Blackout the powder has completely burned in just over 8 inches.  This is true in both sub sonic and supersonic ammunition. So the 10.5 inch barrel you mentioned will have more than given enough time for the full powder charge to burn and developed the maximum pressure possible.  I'm a fan of piston ARs and also the 300 Blackout.  I have not seen a 300 Blackout set up with a piston system.  The piston system does have some advantages in SBRs where the barrel length is shorter than 10.5 inches.  The gun will run cooler and cleaner in those short barrel applications.

Remember just because I have not seen a piston SBR in 300 Blackout doesn't mean it wont work nor does it mean you shouldn't try it.  I would like to hear your results if you do use a piston system.