It could be a couple of things.
As someone mentioned the lock bolt, however Jim’s stocks are CNC cut, that would be an odd issue for one of his kits.
it could be the entry pipe is installed incorrectly causing the rod to bend all of the rammer pipes should be in alignment with one another and the rammer channel,
perhaps the rammer end tip’s pin is not filed flush.
Its possible the rear under lug is too long, if this were the case the lug mortise would be showing through the rammer channel or creating a type of swell into the channel, measure the distance of the lug to the rod, and if that’s where the tension is that’s possible the issue.
Ramrod ends are typically tapered for a snug fit, it’s possible the rod end is too fat.
I would test the rammer hole with some smaller wooden dowels and work your way to the diameter of the rod, if its getting tighter as you go lower, then something is in the stock, it’s possible there’s a wood chip from the drilling or milling. If it gets tighter as you go higher with the dowels then the rod needs to be tapered.