Here’s a modified big-chassis setup. Stock .308 Win. (left) and relocated on a custom .260 Rem. Moving the port really, really helps in this instance. On this topic: Be careful using factory ammo in your big-chassis gun. Reason is that, unless it’s mil-spec, it’s liable to be developed for bolt-guns for hunting use. That can mean the propellant burn rate may not be suitable for semi-autos. This is especially true in the .260 Rem. and .243 Win. This is hardly ever a factor in smaller cartridges, like .223 Rem.