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There is no, zero, none -- nada -- difference in chambers between the LBC and the Grendel. The dies are identical. The throats are different. The Grendel uses a compound throat and the LBC a more conventional throat with more leade.
The case dimensions are the same for the 6.5 grendel and 264 LBC, but the chambers are different, as the 264 LBC uses a .125 bolt headspace and the 6.5 grendel uses a .136 headspace. And yes the throats are different, In my opinion the LBC uses a better throat design.
