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.

 

[Salmonchaser]

Before you go slapping JB weld around and gouging wood try a very slow fire test; take a 10 minute break between shots. When I did it I simply set a timer, cleaned the rifle squeaky clean and waited. Even under warm conditions that was enough time to allow me to closely mimic a cold bore shot. Granted, many rifles perform better after a couple of fowling shots. For this test however you’re simply trying to identify what causes it to string. Getting her squeaky clean will allow you to be the most consistent. I’ll bet you don’t see the stringing. The number ones I’ve hung on to all shot good groups with that test but most would start to string if I shot rapidly. It could be a pressure point in the stock, could be barrel expansion is moving the base. Could be both. I’ve been able to get them calmed down by addressing the stock issue.

 

[Sheltowee]

As several others have mentioned, I suspect the cause is uneven forend pressure exacerbated by the barrel heating up.

 

[Redmt]

Thanks for all the replies and fixes. I should have given a more descriptive original post.
I'll start at the top with replies. It was shot off the bench on bags resting next to the receiver. Trigger pull and breath, this may be part of it. P-ham is sending me some offset rings as the stock Ruger rings give 5"+ eye relief so climbing the stock is necessary and uncomfortable. Yes I know better but I was anxious to try it out after waiting for the barrel to be rebored and 6 groove fluted. As far as a pet load I also know better than expecting one custom load to work in a different rifle. That is the reason we reload,,,,,, I should have started from scratch. The background on this rifle is that it was a 22-250 that I've shot for a year or so. It was very accurate. The barrel was already free floated and the mounting boss epoxy bedded too.
We are still being held hostage by the county with our main roads being closed 24/7 until 10/19 because of neglected repairs. There's no mail, no FedEx but UPS has agreed to deliver on Thursdays as the only way in and out of here adds 150 mile detour. I should probably get the new offset rings by next Thursday if all goes as expected. I'm going to take the rifle back down to bare bones and assemble again. Mount the scope correctly and start a from scratch load development as I should have in the first place.