Lyman's Cast Bullet Handbook lists 15.6gr W296 (aka H110)/39,700CUP as its recommended load for the 155gr #358156 LSWC cast in linotype.
Right next to that is an 18 grain/W296/41,400CUP load for 160gr #358311 (semi pointed/roundnose).** Both are listed at the same 1.590" OAL.
The charge/pressures difference are in all liklihood due to case volume effects of the different bullet shapes (among other things). Beyond that, Quickload tells me that your 16.7gr/LWSC trial produces pressures fully 30% higher than the Lyman-recommended 15.6gr
Drop to 15.6gr H110 and be happy.
** The later Lyman49th drops the H110/W296 charge for their 160gr #358311 (semi pointed/roundnose) to 16.5gr. Their 155gr #358156/LSWC/H110 charge remains topped out at 15.7gr. Read & Heed.
Last edited by mehavey; August 3, 2011 at 09:25 PM.