Yes, bfas go under the flash hider and create the needed pressure, I use those. Issue with these particular rifles is it takes a lot of power to cycle rounds. So the problem is how so you losen up the bolt carrier without sending it out the back of the rifle.
Ar15s do not need near as much power to cycle blank rounds.
Are you already using a HK blank adapter if you are I'm sorry about the post. You might try a sharper degree angle locking piece but you do not want to decrease the unlocked too much or you could cause damage to the back of the receiver buy heavy recoil
Yes, I use a low apature bfa with high power brass. The problem isn't really at the front end. I would like to be able to open up the BFA apature to let more gas out. Beture effect and more consistent cycle. As is with the model gun, you have to go very small on the apature of the BFA to create enough pressure to make the bolt kick right.
On MG42s, I am told to combat this issue they remove the rollers from the bolt... Which seems like a bit much for this rifle. Just considering having a blank fire bolt as well. As a bfa to get more consistent cycling and effect.
I do milsim events so I run a lot of blanks.