might be better off considering a full metal receiver for £35 http://www.taiwangun.com/en/metal-parts/asr-upper-and-lower-receiver-black-aps?from=listing&campaign-id=19
shipping is free on 69Euro at TWG & GF atm, trouble is getting an upper receiver that may or not be 101% compatble with your lower
http://www.taiwangun.com/en/metal-parts/asr-upper-and-lower-receiver-black-aps?from=listing&campaign-id=19