From reading the rules I would think that would put you in the Limited Devision, as long as a jet funnel mag is less then 5.561”. Otherwise you would be in open. Obviously you can't be in production or limited 10 because of mag capacity.
ETA: The jet funnel itself my fall under this catagory which would keep you from competing in limited...not sure though.
External modifications or features such as weights or devices to
control or reduce recoil (such as but not limited to thumb rests or
components which could be used as such).