The module will fit your 308 bolt face,, just tell Hankins when you order what size you want ,I think he has 45-70 and Magnum also, it's a very simple build, take your 308 barrel off screw the prefit barrel on ,line up your lug, headspace on a module, you should be able to open your boat and slip the module right behind the extractor just like you would a headspace gauge, with just a little bit of feel on the bolt when you close the bolt slowly, Jeff Hankins has a video on it also and all he does is in the video is just screw the barrel in with the module in the bolt until it makes snug contact he takes a wrench then on the barrel nut and just smacks it good and it's ready to go it really is that simple, doesn't take much either to test fire it take a look at your primer as long as your primer is flat and it should be everything is going to be fine almost all of the modules the first time I shoot them are very snug they fit much better after one firing. You need a wrench for the barrel nut, and a barrel vice, by the way I have a lot of full shank and barrel nut pre-fit builds the most accurate barrel I've shot so far has been a prefit barrel out shot any of the full shank heavier barrels that I've had and do have today,, good luck.