My strange recurring 5-round groups

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propliner

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I'm shooting a .338 Norma Magnum and the recurring theme is these split groups.

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The rifle prints bullets back and forth like this with 3 in a cloverleaf and the other two touching. There is no sequence to which bullets in the count print where, just the pattern itself. Has anyone experienced or overcome this phenomenon or can you offer an explanation? They are 285gr ELD-M's on the lands.
 
Shoot a 10 round group. My assumption would be that group size is the accuracy of that load in that rifle. Shoot a 10 round group and it should just fill in the group. Just because 2 or 3 rounds are touching doesn't mean that anything outside that cluster (that you can't call) is something weird happening, that's just how the barrel shoots. That's why 3 round groups just don't give you enough data to go on.
 
I'm really hoping it's not just a bad barrel. I had it rechambered for stringing issues previously. That issue is gone now, replaced by this one.

I'll try some different seating depths and work on repeatability in my bipod loading and reticle focusing. I've tried a couple of different bullets and get the same result. Thanks for the tips, guys.
 
I had similar results with one of my rifles a few years ago...swapped out the scope and problem gone. :)
 
I am quite sure the scope is ok. It's a Nightforce ATACR and parallax is set at 100 which coincides with best focus for me. When I was having problems with stringing I tried a Premier which replicated the problem so I eliminated a scope issue back then.

I do have the scope dialed down 60moa at 100yds to take full advantage of its elevation so the sight picture isn't perfectly clear and mirage was a bit of an issue, but I'm an experienced shooter and was able to shoot sub-1/2" groups with my Blaser the same day in between groups with this .338
 
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This has plagued me at times as well.

I put it down to something shifting in the mechanics of the system. Example, if bedding , how the scope is mounted, scope internals ar allowed to move then hang up and then move again.

The barrelled action does move in the stock, but it must 'return to battery' (this is at the macro level) this points to inexact bedding and torque on the action screws. Scope and mounting system must be degreased (de-oiled) and torqued to design specs. The parallax in the scope must be set for the exact range ( don't rely on 300m being 300 m) check this from your position behind the scope until retical is steady on the target.

Another issue can be the management of the rear bag, the more recoil the more pronounced.

Also, with a brake I've found that indexing the brake to reduce /eliminate rifle torque helps here as well. This may have the brake a few degrees of the centerline of the bore.
 
I'm taking the rifle apart today for a re-torque of everything. The bedding looks just perfect but I will check for too-long action screws, a bottoming recoil lug, a ring that might be sitting a hair off its rail lug and again for contact of the barrel.

I've also moved around behind the scope checking for parallax at the 100 setting and there's zero movement. My rear bag is always straight to the target. I remember now that the comb was hitting my non-trigger hand under recoil as it was squeezing the bag. Maybe I should raise the bipod and move the bag further back.
 
i had that to with my 300 norma mag in my case it was a new barrel it was loose i tightened it and it was fine and i used H 1000 i found that to be the best powder with the 210 bergars
 
Scope rail loose, or maybe a switch barrel not tight enough?
Rifle cant after three shots, miss low and off to side...?
Try using double ear pro....it could be your brain acting in anticipation of the muzzle blast from the larger caliber.
Do you get excited about the 3 round bug hole, and shift your position slightly to get the last two shots?
Just spit ballin here...
 
I would try a 10 shot group, don't heat up your barrel too much in the process. Also you may need to move your bullet out to compensate for throat erosion depending on how many rounds you have shot with the barrel.
 
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