jeff houck
posted this
01 October 2016
You're welcome, glad to have been able to help.
After you've made up the first batch of ammo and printed on paper you'll have a reference group size to begin your load development from.
First step is to use as fat a bullet as possible. You don't need to “measure” your rifles throat with anything fancy. Simply ink up your bullet with a magic marker, seat the bullet long in the case and then chamber the round until it stops. Extract the round and look at the marks on the bullet. If you have a scraped mark all around the bullet then the bullet is larger than the throat. Ideally you want the bullet to just barley slip into the throat (1/2 of a 1/1000 smaller). But try it just under and just over diameter. Typically if the loaded round will chamber with a fat cast bullet it will shoot much better than an very undersized bullet.
Second step is to test for seating depth. Again, start with an ink up bullet that is seated to long to chamber. Gradually seat the bullet deeper in the case until it will close with firm pressure but not hard pressure. Check the marks on the inked bullet. What you're looking for are rifling marks on the nose of the bullet (if it's a bore riding nose) and the start of the rifling on the first driving band of the bullet. This is a crush fit of the bullet into the rifling and throat of the gun. Again, use only firm pressure not hard pressure in chambering the round. Also note that depending on the neck tension of the brass, this round may de-bullet when the cartridge is extracted. (OK on the target range but not in the hunting field.)
Now assemble your subsequent rounds of test ammunition with the bullet seated 10/1000 deeper each time. Test for group size with each length of ammo and have fun!
10 shot groups will show you a lot more than 5 shot groups.