Frog , that's more than 1/8 inch. You can file the bottom of the tennon so that it won,t extend into the ranrod groove. You can also file the base thinner before you solder it on. You could also cut a very shallow dovetail and solder the tennon into the dovetail. A combination of these should allow you to get the the tennon on without it going into the ramrod groove. If the hole under the ramrod bothers you, fill it with a small chip from under the buttplate.