It used to be lower rod pipes (the uppers are a breeze), but I have finally got the hang of them, after learning to get the fore end shaped pretty well to final shape before inletting (which goes for ALL parts...don't inlet any more than you have to, thank you Ron Ehlert!), so they're not so bad anymore.
Absolutely the most tedious, time consuming, utterly excruciating thing to do on a gun is making, fitting, inletting, drilling, slotting and pinning barrel tenons. Hands down. NO competition. Nothing else even comes close. The slotting is a special PITA. Takes me about four solid hours to finish four barrel tenons and get the barrel secured in the stock, and I dread the task almost as much as going to the dentist.
This is what I should have a little apprentice boy for.