As mentioned above the other three extensions are different. They are made to ONLY take the same size bolt it was shipped with. You can not put a .470 bolt in a .540 or .585 extension. You can take a .470 and use it in another .470 extension. I think Barrett did this to make the gun GI proof. Notice these bolts are the same and can be used in either extension. My 300 PRC bolt (not shown) also has the cut out at the rear of the bolt and will not fit into these extensions nor my original 300 WM extension (non cut out bolt) nor any other size extension.
Keep in mind I am not addressing differences in headspace from one bolt to another within the same bolt face size from extension to extension. Headspace needs to be set for the bolt you are using with the extension being used.
Hopefully my explanation makes sense.
Keep in mind I am not addressing differences in headspace from one bolt to another within the same bolt face size from extension to extension. Headspace needs to be set for the bolt you are using with the extension being used.
Hopefully my explanation makes sense.