I wish I could give more specific guidance, but as I stated my info is second hand from a few weeks or research. I dont have any low mass stuff but I have considered building a race rifle.
Think of it like this. Lower mass equals less stored energy. Less stored energy means less reserve to make things "work".
Now you can "tune" the gas pressure down to only what is needed to move the low mass items and overcome things like the drag caused by the loaded magazine on the BCG just to name one. But the total energy transfered from combustion to moving parts is lower, that is what narrows the safety margin.
Remember, things that are in motion tend to stay in motion unless acted on by an outside force. The mass of those items in motion directly effects what "counter action" is required to stop or lesson that movement (like the mag drag on the BCG).
You may be able to "tune" your system down so light and low pressure that a mere cricket fart on the BCG could cause a short stroke...

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