Vertical shot string

[Redmt]

Question for all the reloading wizards. I've heard of vertical shot stringing but never paid much attention to the threads. I'd never seen it until now.
I broke in the barrel on my custom 6.5 bored #1. I figured I would start with a known load that produces excellent results with my Ruger Predator. I've been shooting the same load for years. So same load, completely different rifle and I got an S shaped vertical string about 6-8" with 5 rounds. What do I even start with looking for the WTF?

 

[Coule stalker]

what is your shooting position? The S shape sounds like potentially a combination of trigger pull and breath… I recommend starting completely over, it doesn’t sound like the new rifle likes your pet load. I’m no expert, but I always start with new brass, or shoot some higher quality factory ammunition and keep that brass for that gun. If you like your pet load components, back off to the book minimum and work up from there.. sometimes just a primer change makes big changes..

 

[Coule stalker]

I should have mentioned in my first reply, when I see vertical I start thinking about increasing powder charges… if there is a lot of horizontal, I start playing with seating depth.

 

[Salmonchaser]

Very common issue with #1s. Dealt with it with my 257 Roberts, 275 Rigby and the 300 H&h. Free floating the barrel, bedding the spring hanger as well as bedding the interface between the fore end and the receiver helped significantly I thought I had done a pretty good of that. P ham did it better. I also installed a Hicks accuriser, it helps also. Prior to my efforts I could go three shots before seeing vertical stringing.
With PHams bedding I fired 40 rounds, slowly, working on load development, no stringing with 8 differs loads.
Also you will settle the rifle down by putting the front bag at the back end of the forearm, next to the reciever.