I had a gap behind the barrel on rifle(not a Kibler) I was building. I glued a piece of popsicle stick in the breech end of the barrel channel and inlet the barrel breech. By the time I shaped and stained the stock. It looked normal.The in-letting on my Colonial was very good - but not flawless.
The lock mounting bolts lined up perfectly with the holes drilled through the stock, but there was over a 1/32" gap behind the barrel and behind the tang. Filled in with some wood putty. Maybe somebody didn't get the stock correctly mounted in the machining fixture for that procedure. Still have a ways to go in my finishing effort - hope the putty stains OK. On the plus side, some of the processes detailed in the Kibler assembly videos are now completed before the kit ships. Overall, still very pleased with the kit.