I found that out too I wasn’t paying close enough attention; had the tumbler inlet but couldn’t figure out why I couldn’t move the cock. Then it dawned on me the stock was interfering with the cock. It fit okay at the full cock position and the fired positions but not at half cock LOL! Thankfully I didn’t mess anything up. I think the book Recreating the American Long Rifle says the cock should be off or some wood removed as you show. I spent several hours yesterday filing and sand the entry pipes; my fingers are sore today. LOL
When you take the stock down for the loading rod and or barrel do you what do you recommend; a rasp, plain or other. I ordered a rasp so I sit and wait. Rasps aren’t cheap I found it difficult to find a good source; Wood Craft is very expensive. I don’t understand why i can’t find affordable wood rasps the rasps from them are made in France id like a few made in the states it doesn’t have to be hand made just do what rasps do.