Perhaps the barrel whip that you are so accustomed to experiencing can be relieved by a harmonic balancing dampener. But if you are so assured the flex which will exist in a rifle which is not even built will occur then, get that heavy duty handguard. The larger frame AR10/LR308 is not the same as an AR15. Hey what do I know ,I'm just a shade tree gun disassembler who has only put 150+ AR's together !
Don't watch Judge Judy ,but take her advice ...K.I.S.S. !!!