gas system length and gas to face question

[LRRPF52]

Few ways to reduce blowback
Reduce gas (adjustable gas block)
Reduce barrel pressure (less efficient can or longer barrel)
Increase cycle time (longer dwell, more mass, different cam pin timing)

They all help, but adjustable gas block is the fastest and most effective way.

I run a 18" intermediate length gun with an ultra 7 with 0 gas face. Heavy buffer and an slr block.

I've also run suppressed 556 sbrs with proper sized gas ports with 0 gas face.

Over gassing is the main issue, every other solution is a bandaid.

Are you using any particular charge handle?

Is your Ultra 7 a 30 or 6.5?