I have a light rifle in an MPA ultralight chassis. I am looking for a detachable weight box for arca rail (not a weighted arca rail) for when I am just prone on a line and want to push weight up without a need for multi position or mobility. The rifle is just around 12lb sans bipod now. I saw one once at an ELR match on a MPA BA COMP and cant find it i think it was an alumn box you filled as you liked but i am uncertain.