Does any company make a blank sleeve to use in place of the gas block.

[Klem]

It takes a lot of effort to pull back the BCG when there is no gas. The system needs at least some gas for primary unlocking. Probably the easiest way to demonstrate this is as Cereal is saying, remove your gas tube while leaving the gas block in place. Fire a shot and see how sticky the BCG becomes. It's not much fun doing this more than a couple of times.