Building a upper, not for competition! Was wanting a gas block with the flip up sight incorporated. For simplicity, but noone makes one for a bull barrel. Everyone I have talked to uses the magpul (don't know if theyve had to replace them). They have had problems with the troy and yankee hill moving even after a little lock tight, the versions that attach the gas block. One guy uses a one peice yankee hill that is the sight and gas block incorporated together. Does anyone know anyone who makes one in bull configuration?