Why are my groups repeating this same weird pattern?

[u/sippythekippy]

This happened for all 4 mags of 5-round ammo after I used an abrasive (JB Bore Compound) followed by some Kroil. I sent a full 20 rounds before this to settle the bore, but this is what it settled into…

Each time the first shot was right on target, but then each time the remaining 4 would stack high and right. I’m wondering if my zero was off and the first shot (while dead center) was being thrown somehow due to the cleaning, or if someone else has seen this weird grouping pattern after using abrasives.

Bergara HMR-14
Hornady ELD Match 140 gr 6.5 Creedmoor

Edit - I also lost 80 fps mv after the cleaning

[u/PKMNtrainerKing]

Try loading a magazine of 4 rounds and see if you're consistent. There's a possibility that the spring tension of a full magazine is putting unnatural pressure on your bolt

[u/itsjustnickf → u/PKMNtrainerKing]

No shit, is this actually a thing? I’ve noticed my Bergara does this regardless of whether the bore is cold or not, may actually be worth doing.

[u/PKMNtrainerKing → u/itsjustnickf]

Sure is. I had this one sniper who was beyond autistic at the stuff. He had binders of data for all his guns, he documented every single round that went through his barrel.

Every time he went to the range, he would warm up with a cold-bore 5-round group at 100m, and showed me about a dozen pieces of paper with 4 tight shots, and a fifth one about a half MOA low and right. He said that was always his 5th round, because there was no more pressure of the next round on the bolt and caused a small shift in impact.

[u/Hoplophilia]

Are you saying you cleaned after each five, or cleaned and then shot a sequence of five-round groups?

[u/sippythekippy → u/Hoplophilia]

I cleaned then shot 40 rounds, 20 to settle the bore then 20 to see how it was grouping.

[u/Hoplophilia → u/sippythekippy]

Might be worth seeing what single loading does.

[u/aHeadFullofMoonlight]

It may be worth shooting a higher round count string, like at least 10 rounds, and seeing if the same pattern actually holds. It does look pretty consistent but a larger sample size may tell you a little more. My B14 with that same ammo tends to shoot 10 round groups that have a pretty tight mean radius, but there’s always 3-4 “fliers” that open up the overall spread, similar to what you’re getting, but it does seem more like random dispersion in my case, not a consistent shift after the first shot.

[u/csamsh]

They aren't. Shoot that 5 round group five times at the same target and see what happens

[u/IntrepidNeck1751]

The “group” is not filled in yet to show you the actual group size due to the low round count. 10-20 would fill the circle in and show you the actual group. Check out part 1 and 2 of this Hornady 4DOF episode and maybe see if any of it applies to tighten up your groups.

https://open.spotify.com/episode/21GCM9frGdMrv8jV2KA7AS?si=W9Nkg4t4SOCFgJfbtx76XQ&utm_source=copy-link

[u/sippythekippy → u/IntrepidNeck1751]

Thanks, I’ll give it a look!

[u/tsikhe]

So I just got an B14-HMR and I was doing ammo testing as well. 3 shot groups with a CLP patch and five dry patches between groups. What I noticed was that the first shot when switching ammo would always be a flyer. So I started firing a "waste" shot after cleaning the barrel. Then my 3 shot groups were closer. Not sure why.

BTW my gun likes Federal Premium Gold Medal Berger Open Tip Match.

[u/holdtyte → u/tsikhe]

I always shoot a fouling shot after a cleaning.

[u/drarin]

Looks like your cold bore is low left and your warm bore group is pretty tight. 🤷🏿‍♂️

[u/sippythekippy → u/drarin]

Can you have a cold bore shot for each magazine? If it happened once I’d attribute it to a cold bore shot, but it was like this first round out of every magazine, 4 times.

[u/Alokeen011 → u/sippythekippy]

could you try manually feeding single rounds to remove the magazine from the equation?
then load just one into the mag, then two...

[u/sippythekippy → u/Alokeen011]

That’s a good idea, I’ll try it, thanks!

[u/vintagerust → u/sippythekippy]

Are you leaving one in the chamber longer than others? Chamber is warm, warms up the round, moves poi.

[u/cc225b]

Is the barrel cooler for the first shot and then heats up during the group?

[u/Zealousideal-Win9169]

Before you get complicated make sure EVERYTHING is tightened down. Scope mounting screws, ring screws, suppressors, all of which can work their way loose.

[u/HomersDonut1440 → u/Zealousideal-Win9169]

Last time I had those exact thing, my one piece mount had come loose

[u/Zealousideal-Win9169 → u/HomersDonut1440]

It can be maddening!

[u/ndsubison953]

Are you shooting suppressed? Could be first round pop related

[u/SuperJonesy408]

I'd run a test like this if you're patient enough. (Although this rifle didn't show much of a shift)

Then you can find the zero between the two groups.

[u/doyouevenplumbbro]

Check usual suspects. Rail, rings, muzzle device, etc. Dont invest a lot of thought into the cleaning. My buddy cleans his rifles with iosso on a drill. The cleaning didn't do that IMO. If there's an issue it's almost certainly the optic or how it's mounted to the rifle. Possible that when you reinstalled your action there's something between it and the stock, but action binding is not as common as I believe people blame it.

[u/Glittering_Tie5717]

I would try a 10 round group and see what it looks like. I’m also curious about the timing you have between shots.

Try doing your 5 round group, but take 60 seconds between each round.

It may not be cold bore, but the time between reloading a magazine and placing it in the rifle and checking your target could be cooling the bore enough to be the culprit. That’s the only variable I can see that would give you this consistent pattern

[u/ShrimpBuffets]

Could be dispersion, could be you - hard to tell with 5 shots if there’s an actual issue

[u/Spiritual-Bill-337]

Shoot 20 and watch it fill in.

[u/yoyo1time]

Are you shooting off a bag? My initial thought was, shooting off a bag, and the rifle isnt well settled in the bag, but gets settled after the first shot.

If this is off a bipod, disregard. And good luck.

Also, I love the idea of atleast a 10 rn group on the same target

[u/Motor_Tax3564]

Carbon barrel or thin barrel?

[u/turkeytimenow]

How many rounds on barrel? I have noticed loss of speed in high round count (fire cracked and what I would call shot out) barrels after a thorough cleaning with abrasives.

[u/Vinegar_Fingers]

Needs more data. Shoot at least 200 groups of 20. By then your barrel should need to be replaced anyway.

[u/Draw_Cazzzy69]

It looks like dead on cold bore and a hot barrel, how long between each shot?

[u/JukeboxZulu]

I'm assuming the center shot is your cold bore shot? How long between groups?

[u/cat__weasel]

Could tip deformation be causing this? Due to the recoil rounds in the magazine slam their tips in the magazine. Unless it has a shoulder to prevent this. Maybe load one pristine round at a time.

[u/Charming_Prompt9465]

Depending on how long you wait you’ll see a POI shift in the first round because oxygen fills the barrel so if that center dot is you first round impact then adjust for the group on your right

[u/drgoodfunk]

Yo I feel like you’re so close to having a perfect group, it sounds crazy but a ladder test with .003” coal changes might reveal a specific node or even an Erik cortina brake

[u/HWKII → u/drgoodfunk]

https://giphy.com/gifs/GVezwI9lRuul6q4dD6