have same issue about L1 here. what gun is suited for this ship actually?

fyi, my gunner at lvl 89.

I'm using lv 91 16"L with 103 gunners. Nice spread and everything 

The proper guns for the L1 are the lvl 91 trip 16" mark 4 L, until then use the mark 2 trip 16" guns which were part of it's real design.  You can use the Hoods dual 15" mark 3 Ls if you want a to be a a high lvl renown/repulse for the laughs

Use the level 91 16"L trips. There are been some updates in the last 4 years, and I know at least one of these included the L1, although I cant remember what the details of it were. Just remember that RN is supposed to have one of the highest damage per shell but a low range. Unfortunately the introduction of the two new navys have turned things around a bit. RN is not really as big a threat as before as they deal out damage from a greater range. So basically what they have done is stick in a load more ships that outrange you. You just need to choose your position and the time to rush in carefully. Then you should destroy as I do :).

GL and HF being outranged... 

any advice how to fight RM BBs with L1? its really pissing me off if i had this ship in my line >.< im using 0.9 belt but its still useless to handle the bullets came from that ship.

0.9 belt is useless against bb guns

Could probably try to kite him i mean you do have hang time on your side.