50-90 paper?

[Gunner500]

A lot of vertical starts with barrel harmonics, light and head/tail winds, bullet release from the case mouth, Inside case volume that will change the compression that changes the powder burn.
Find the vibration null on your barrel and mark that spot with something that won't leave a mark. I use a rubber band that is tight. You can find the null by holding the rifle at it's balance point and slap the barrel with two fingers or a rubber mallet something that won't hurt the barrel. You don't need to hit it hard. You will feel a vibration in your hand holding the rifle. Tap the barrel front to back or the other way till you find the location where you don't feel a vibration when you tap the barrel, this is your null point and mark and measure this point for future reference.
This will eliminate some vertical. Horizontal can start with the guy behind the butt plate fat fingering the rifle, improper cheek weld, this also will effect the vertical. Seating depth of the bullet in the case can also cause horizontal strings as well as wind.
Uneven wood to barrel contact can throw verticals as well as oblique strings. I had bad vertical problems with one of my rifles so I bedded the whole forearm with acraglass and that solved that problem a whole bunch.
Free floating a falling block rifle is not an option.

Forgot an important point and that is holding the sight straight without canting it. A 10 degree cant will throw the shot from the X ring to the 9 depending the left or right hand twist in the direction it will travel at extended ranges.

WOW! Thanks for all that Kurt, I will put it to use asap, meanwhile a little update, 26 degrees outside, wheeled diesel fuel blast heater on casting porch, ambient temp bouncing off metal shop wall hitting me in the back is hotter than standing over the pot!

55 beautiful bullets cast, didn't take long to cool, weighed 10 bullets, average weight 705.4 grains, heading in to patch, will be back.