If you buy the new parts kits they do not come with a barrel! This is good and bad. The bad part is that you need to find a barrel for your build and then buy a trunnion. After that you need to Align the barrel and trunnion then drill out the retaining pin then fit the assembly in your build. At this point you should start to see the many problems you will face (alignment). Good side is that with out barrels you skip all of those steps and just tack weld the barrel then remove it and run a bead on both sides. So you can see a lot of time saved and less hassle.