What causes a group like this ?

[TaperPin]

Wow that’s really vertical. I don’t have anything to add other than I wouldn’t put much effort into this one combination. Even if tuning the load shrunk the huge vertical, you’d be at the mercy of the tune and conditions, lot variations, barrel wear etc will keep you chasing the tune. It might not be warranted, but I get excited with skinny groups since the hopeful optimistic side of the brain is sure there’s a load just as tight but in both vertical and horizontal.

Even though other loads fired the same day didn’t seem to produce the same vertical, this load might be showing a rifle issue that’s right on the verge of causing strings and this load just puts it over the top.

As always with stringing like that, check the barrel isn’t vibrating against the barrel channel, or something like a sling swivel stud hitting a hard leather front bag. If you’re using a bipod on a hard surface, watch for even loading of the legs or try a piece of fabric or carpet under the legs if you don’t preload the legs.

If you find other loads start causing vertical problems as you reach max velocities, in addition to normal rifle checks I’d also swap the scope. I had a scope with a loose internal lens that created stringing as recoil moved the lens up and down - it wasn’t until the lens completely fell over sideways inside the scope that the stringing was figured out.

Good luck, my optimistic side thinks you’ll find a good load right around the corner.

 

[centershot]

 

[5811]

Source for this?

 

[centershot]

5-Shot-Group Shapes: Here's What They're Telling You - RifleShooter

If you're a handloader, chances are you've wondered what the different 5-shot-group shapes really mean. Vertical, horizontal and diagonal strings, double groupings, and scattered shot-group shapes tell you a lot about your barrel and load recipe.

www.rifleshootermag.com

 

[Fireflyfishing]

My assumption is that powder is a no go with that combo.

 

[mtnbound]

Agree 100%. Feel stupid for asking for exact reasons you describe.

But this is a learning experiment for me too with reloading and ballistics.

I’ve been an archery guy my whole life - there’s not much about a bow or arrows I don’t know or understand. I’m trying to crash course as much as I can with firearms.

I know how they go bang. But I’m running two tracks at same time - get efficient useable results quickly without fuss ; learn as much as you can in the process. It’s costing me a few hundred dollars in range fee and components. But seems worth it - and I could hunt tomorrow if pressed.

Been there, done this.
The problem with "running two tracks at the same time" is the tendency to get sucked into why this combination is doing what it is doing, in which you chase your tail, wasting resources and time. If the powder/bullet combo doesn't do what you want, switch one and try again. IMO, it seems like reloaders fall into two groups: one reloads to shoot, and one reloads because they like to tinker more than shoot.

 

[Wrench]

Would you do this even if multiple other loads shoot round groups before and after that vertical group? And repeats twice with same bullet/powder, but no others.

Seems like if I missed on assembly, it wouldn’t be isolated to a single load out of a session.

I did build gun from ground up and follow protocol of getting everything disassembled, degreased, loctited and torqued. Across around 300 rounds or so, the only two groups to string vertically were 95tmk’s with 8208xbr

It's a dasher. If it didn't shoot, I'd check mechanics, swap optics and try one more bullet. If that didn't do it.....I'd punt.

A poor shooting dasher should shoot a group that size at the 300 line.

 

[Ckat]

Vertical stringing can indicate being just out of an accuracy node. I would normally suggest trying 0.3-0.4gr less powder and 0.3-0.4gr more powder to see if the issue resolves; but since 0.4gr more shows pressure signs, I would only recommend dropping the charge 0.3-0.4gr.

 

[farmermail]

All great advice. I have also adjusted lug torque to help stringing. Starting with factory specs, don't be afraid to go up/down a couple inch/lbs to see what that may do for you.

 

[Harvey_NW]

That is a perfect example of random distribution and small sample variability. Those group shapes mean next to nothing, and most of what is written is just theory that's easily disproven with larger sample sizes.

 

[Harvey_NW]

I'm not familiar with 8208, but in a 16" barrel and bad stringing I assume it might be inconsistent ignition. This episode of the Hornady Podcast explains it much better than I can, and is a worthwhile listen.

 

[centershot]

That is a perfect example of random distribution and small sample variability. Those group shapes mean next to nothing, and most of what is written is just theory that's easily disproven with larger sample sizes.

If 3 or 4 don't group, 10 sure won't.

 

[mainbeam pursuit2]

Centershot has provided a great resource about groups. Look up Jack Neary(hall of fame benchrest shooter) on youtube, he has some good info on groups.

 

[KyleR1985]

33 posts, and a dozen or so different potential causes.

Looks like I’m selling one of my kids for some Varget!

 

[tap_city]

I have struggled with my 16" 6Creedmoor with common recommended powders which results in incomplete powder burn (because they are slower). This has caused a lot of headache and I've gone through about 200rnd of testing before landing on using N150. 90%+ of case capacity and 100% burn are needed to get consistent combustion. Out of a 16" barrel you need powder on the faster side but without over pressure to get a decent velocity. For me with N150 I can get single digit ES across a gr of charge weight.
Do you use GTR or Quickload to model?