Have a fusion (which is not unlike what you are asking about) and an OLD QB bulk fill end cap.The fusion to the left/ old QB to the right:I tried swapping the bottom piece. On the QB, it does nothing but hold the spring that powers the inlet valve. With the Fusion bottom piece in place, it pierces a 12gr. AND holds the gas in.Bottom sections being swapped:What you end up with is a bulk fill cap that will also pierce 12gr.So if you are using 12gr, that bulk fill cap will pierce the top 12gr just like the issue cap (and the vlave in the end cap will keep the co2 inside the gun and not vented out). If you want to run bulk fill, it works just as well as any bulk fill end cap works.
Nice idea! How many shots does your Fusion get with HPA, before the shots start dropping?