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Other than the RETech NPAS, you can cut out a custom shim from an old credit/debit card and glue it to the back of the stock nuzzle plunger. It's rough and rather dodgy but it allows you to play pretty much mediately. I personally got my CQB rifle from 400FPS to 250FPS and it works great so its up to you if you want to do it and maybe make the shim slimmer and the FPS higher.