LMT gas blocks are press fit. But for the average Joe, it's not really an option. But I get what you're saying. The BCM blocks are pretty tightly toleranced, unlike some I've seen that would practically spin on the gas journal. With a BCM, what little space there is, will seal itself off pretty quickly.I am curious why not make a "press fit" style gas block with a reduced inlet port?
I know pressing the gas block on would not be a home job for many, but using a bearing heater or hot plate to heat the gas block before installing would create a tight seal once installed/cooled and eliminate the possibility of gas leaks around the block.
This would keep barrel options open and allow you to go back to normal gas if you wanted (if you were able to get the gas block back off that is....)
Below is a CAD (crappy ass drawing) of what I am trying to explain.
View attachment 12551
Edit: It would possibly work as a non press fit, but I just feel it would has gas leakes around it otherwise...
But the more important factor is the gas hole in the barrel or in your example, the block itself. Making blocks with gas holes in multiple sizes for standard and lightweight profile barrels is probably not economically feasible.
The good news is that someone has figured out a better solution for over gassed barrels, without requiring moving parts like an AGB. Black River Tactical makes a series of inserts that can be threaded into the gas block to reduce gas flow.