Also, It hasn't been explained, if any/ one of the return springs has been cut down/ Omitted either. To overcome the Differing pressure of the STRIKER Block Operating spring.
That’s a good question. The striker spring is absorbing some of the energy of the recoiling mass. But that energy is not released to close the bolt. Instead the energy is stored in the striker spring until the trigger is pulled.

The carrier and breach block must still be pushed into the locked position (and now held there) by the return spring(s). So, the man with the white stick sees the physics of the semi-auto quite clearly, I would say.

There has to be a balance between the striker spring and the return spring(s). The return spring(s) must have enough energy to close the bolt. And the striker spring needs enough energy to drive the striker. If too much energy is stored in the striker spring, there might not be enough energy put into the return spring(s) to close the bolt. If not enough energy is stored in the striker spring, the result would likely be light primer strikes.

Finding the right balance between the springs is what we call “tuning the springs.” It’s basically the same process for a lot of machine guns that are converted to semi-auto only. Some are striker fired and others are hammer fired. The energy for the striker or hammer spring is often taken from the return spring by shortening it or replacing it with a weaker spring.

One very nice thing about the Bren is the adjustable gas system. It lets you easily regulate the amount of energy being put into the springs to a degree. The MG42 is recoil operated. To make adjustments you have to change the return spring and/or the booster. It’s not difficult, but you have to have the parts with you. With the Bren you just change the gas setting.

I am guessing “light ball” needs a higher gas setting than “heavy ball”?

H/Spacing is insufficient If this is the case, then it is NOT correctly locked up when firing. & the pressure generated combined, WILL indeed cause this problem.
The locking shoulder should arrive today. The flooding we have been having here might have slowed it down a day or two though. If it doesn’t cure the blowouts, the springs might need tuning.
The return spring rod passes inside the striker spring on this design. If the striker spring is contacting the return spring rod and creating friction, a stronger return spring might be needed.