Step 14: Joining the barrel assembly and ammo barrel step 1
Putting it all together is actually simpler than it sounds. The ammo barrel and the gun barrel just need to be bolted together.
Start by cutting a length of the 1/8" steel, I would say around six inches or so. Drill a 5/16" hole near one end (and yes, I would buy a bit for this, I did in the end, dremeling out a 1/4" hole to 5/16" in steel plate is not fun) and put it on the right side of the 5/16" threaded rod that the handle assembly attaches to.
Bolt it in place and position the ammo barrel where you want it to go. Keep in mind that at least some of it needs to be in a straight line under the middle of the barrel (for the rear connection point of the rear handle) and it needs to be far back enough that the third connection point between the barrel assembly and the ammo barrel can be made, however it should still be slightly off center to the right of the barrel assembly. The description is a bit awkward but the pictures of my build and the source images you should have studied will hopefully help it make more sense.
Mark on the ammo barrel where the piece of steel intersects with it and, using a dremel, cut a slot for the steel. Slide the barrel down on the steel until it is the proper distance from the barrel assembly, this is also fairly subjective but mine is around 2 1/2" beneath the barrel assembly.
Mark the point at which the steel meets the barrel then drill a hole on either side, fit the steel back into the barrel and put a bolt through both holes to hold the barrel in place.