Got a new barrel on at the same time went to
Adams piston set up and can't get any better
than 2 moa @ 100 with and combo of ammo
69smk 55bthp and any powder types.
I have heard that there is a slight lose of
accuracy but form .75 moa to nothing under
2 seems a little excessive.
20 inch with a 1/8 twist
Had a first run blackhole weaponry and now
have a voodoo..

pretty much.
was having a mental rant when I posted it

That's how I read it. My answer is Yes, it might be the barrel... or it might be the piston system, ... or it might be some assembly error.

There are two approaches to modifying complex systems:

1. Change multiple components all at once and then test. When it goes FUBAR, put back known good parts one at a time until it un-FUBARS. The last thing you took off stands a good chance of being the problem.
2. Change things one at a time and test. The last thing you installed stands a good chance of being the problem.

OP has chosen option #1.

I'd put the gas system and DI BCG back on the rifle and I bet that barrel drives tacks.

ETA: Bring on the "There are more than two approaches" posts. Yes, I know that, N/A in this case.

No DI pieces around anymore..

Adams Arms website says the gas level is adjustable. Is there an OFF position you could select and try single shots? Use the charging handle to cycle through a few mags to check grouping / accuracy of the barrel as installed? That would take harmonics from the piston system out of the accuracy equation, would it not?

Great Idea that I never even thought of..
Will make 50 some time this week and give it a shot..

Wonder if the Adams rep would have anything to add to this discussion.

I shoot .75 moa with my AA piston setup on a Rainier Select 5.56.  I was honestly shocked at just how accurate it is with 69gr SMKs and Varget but it showed me there really is no loss of accuracy.

As for harmonics there is no difference between that and a DI gun as the projo is gone before the piston system begins to move.  At that point it's just another gas block.  

When reloading you pretty much have to start a new load ladder when going to a new barrel.  Barrels from the same batch will still like slight differences in loadings.

Might want to look for any imperfections in the barrel, especially the muzzle crown or burrs at the gas port.  

Might also want to make sure nothing is in the path of the piston action that could be inducing torque into the system.  If any contact exists between the AA gas block and the handguard you aren't free floated at that point which can have an impact on your (points of) impacts.  The piston itself should not be in contact with the gas block when at rest.  You should be able to slide a couple of business cards between the end of te piston and the block itself.