Accubonds Tumbling?

[grizzly_]

Can wind cause a bullet to tumble? I was shooting steel at 330yds with a load that has been highly accurate. My camera picked up the bullet approaching the target and it appears to be flying with a corkscrew. Thoughts?

It's a 180gr Accubond out of a Cooper 92 in .300 Win Mag.

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[ImBillT]

Wind? No. Insufficient twist for the bullet and conditions? YES.

Frame by frame I never saw the tip pointing backward, so I don’t know that tumbling is the right word, but the flight path seemed to be quite erratic. I assume that was extreme tip wobble that was on the verge of fully tumbling.

What twist barrel, what Accubond, what elevation and what temperature?

 

[grizzly_]

Wind? No. Insufficient twist for the bullet and conditions? YES.

Frame by frame I never saw the tip pointing backward, so I don’t know that tumbling is the right word, but the flight path seemed to be quite erratic. I assume that was extreme tip wobble that was on the verge of fully tumbling.

What twist barrel, what Accubond, what elevation and what temperature?

I agree that tumble may not be the right word, that's why I changed it to corkscrew in my post. The round appeared to hit the top edge of the steel so it was still somewhat accurate.

I'm not sure of the twist in that barrel. It's the standard white-tipped Accubond. Elevation was about 4300' and it was about 80F. They're handloads with 66.0gr of IMR4350 with a stated velocity of 2990fps, though that's never been chronographed.

For reference, this round has shot well in the past


Also, the next two shots were at 545yds and both hit so I'm not sure accuracy was affected much. I don't know if they all fly like that or if it was just a fluke, but I'm definitely not a gun expert.

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[grizzly63]

Stick a patch on a cleaning rod. Insert in barrel, mark the rod, push in until it makes a full turn. Measure the turn distance.

 

[grizzly_]

K. And what would y'all consider an acceptable twist for that round? Is it possible to just get a bad bullet?

Knowing that gun will regularly shoot close to 1/2 MOA with that exact round and that I can hit steel at 545 yds three shots in a row (two by me and another by my dad) in that crosswind, is it really that likely that an erratic flight like seen is typical or is it more likely that was a one-off round?

 

[std7mag]

Seeing the bullet from a 300 Win Mag at 300 yards leads me more to thinking it's a cartridge issue, not bullet issue.
Same with the rainbow trajectory.
Looks more like a really light powder charge.

That cartridge, with that bullet at that distance, you might pick up the vapor trail with a good spotting scope. But to see the bullet...

Note, a light powder charge may actually recoil more than a full charge of powder.
Cases with large capacity can get large spikes in pressure sometimes if loaded below 85% case fill.

 

[cahunter805]

I’m thinking it was a fluke with a bad bullet. Maybe the tip fell out while loading and you didn’t notice. Accubonds can have tips fall out.
Your powder charge is on the low end also. Have you shot higher charges say up to 70gr?

 

[grizzly63]

1 in 10"

 

[grizzly_]

@grizzly63, it's a 1:10 barrel

@cahunter805, I loaded a half dozen different loads that I thought would make good hunting loads and the Accubonds were the most accurate, I then loaded several different powder options and this load was the most accurate. As the round sped up, the group really expanded for some reason. I'm sure I could tighten things up with Match ammo but that's not why I bought this gun. My primary objective with this gun was to get one gun/round that I could hunt anything in North America with and I feel like 180gr Accubonds from a 300WM fit that bill pretty well.

@std7mag, I think you might be on to something with that cartridge. Either it was a bad bullet or, more likely, I somehow screwed up that load and didn't get the right charge in it somehow. I'm super careful but I'm sure we all make mistakes. That video was just with my cell phone through a spotting scope and then turned down to 1/2 speed... that bullet should be moving way faster. (Notice the difference in the 545yd shot.) I can't explain how it went OVER the target if my aim was good and it was moving slower but an erratic flight path could probably do just about anything.

I'm going to chalk it up to a fluke and not worry about it.

Just for fun, here's the video taken while I shot my Desert Bighorn with this gun a few years ago. They're older fellas and had a tough time figuring out their camera and were suprised by the delay in the sound of the shot so their commentary is pretty funny.

Thanks for all your help!

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For the sake of clarity, I shot him initially while he standing at the edge of the rock. He was dead and just didn't know it. He ran those few feet and locked up so I hit him again to anchor him.

 

[std7mag]

Poop happens sometimes.

Even with a light charge, it may shoot high.
Bullet leaving the barrel at a different time in the barrel harmonics.

If the one shot was an anomaly, mark it as that, especially since no one was hurt.

 

[ImBillT]

Without wasting time on a twist calculator I’d say 10” should be fine for a 180AB.

Could be that the core was slightly off-center of the bullet, which is cause by inconsistent jacket thickness. Until fairly recently jacket concentricity was poor across the board, but we didn’t watch our impacts with high speed cameras then either. The thicker the jacket is, the harder it is to make it perfectly concentric. While ABs shoot pretty good, if someone was to prove that they occasionally have a bullet that’s a little off, it would not surprise me.

There could be other possible causes. If you’re shooting with a lot of jump and full length sized cases in a non-match chamber you could end up with a bullet hitting the rifling a little out of square, which might also induce some tip wobble.

 

[grizzly63]

I understand the one gun that does it all thing. It can be depressing if you have a magnum and it will only perform like a lesser cartridge. Each rifle is different, some run hot, some dont. Sounds like you have the hunting figured out. I would go with the anomaly theory.

 

[mtmuley]

I understand the one gun that does it all thing. It can be depressing if you have a magnum and it will only perform like a lesser cartridge.

I've never had that feeling. mtmuley

 

[grizzly63]

I sold that rifle to a guy from Montana.