This is Weird: Fibonacci Spiral on Target

[Honey Badger282.8]

I was shooting my new Aero Precision .300 build for the first time and was sighting in my red dot. I bought the stores demo red dot and didn't have a bore-sight so I started at 10 yards to make sure I was on paper. I shot about 20 rounds of this ammo and noticed some weird spirals on the target. At first, I thought it was keyholing, but it's not. The spirals had tears that followed the pattern which made it look like a keyhole. When pressed flat, the bullet hole is normal. The guys at the range had never seen this before, but my guess is unburned powder. The box of Fiocchi that I switched to had zero issues and was much more accurate.

10" Aero M4E1
155 gr FMJ
10 yards

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Original Scan Here
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[izzy]

Don't know what it is but the image of the round hitting the target in slomo is pretty neat.

[C Ward]

Bullet is shedding the jacket and coming apart , the spiral is lead being slung by centrifugal force .

[Irving]

Bullet is shedding the jacket and coming apart , the spiral is lead being slung by centrifugal force .

So what you're say is, he's curving the bullet?

[Wolfshoon]

Neat. What brand ammo were you using before the Fiocchi?

[Honey Badger282.8]

Bullet is shedding the jacket and coming apart , the spiral is lead being slung by centrifugal force .

Wow. I never would have thought that could happen.

[C Ward]

Usually really thin jackets combined with sharp or too tight rifling .

Plated bullets are also well known for doing this .

[Honey Badger282.8]

Usually really thin jackets combined with sharp or too tight rifling .

Plated bullets are also well known for doing this .

Interesting. I'm fairly confident that it's a thin jacket as the barrel is perfect.

[brutal]

So what you're say is, he's curving the bullet?

That was my first thought.

He mastered the technique.

[bradbn4]

thinking it is a mixture of a few things - but the bullet getting naked by tossing off the jacket seems part of the answer - what is the twist weight - and dang, going to have to hunt down that funky movie now - I remember the ads

Also the ammo - does it show a rated speed, fps?
10" barrel, kind of short to be shooting the high(er) speed ammo

[Irving]

10" barrel, kind of short to be shooting the high(er) speed ammo

I thought that .300 blk burns up all the powder within 9" of barrel or something like that in any weight bullet.

[Honey Badger282.8]

thinking it is a mixture of a few things - but the bullet getting naked by tossing off the jacket seems part of the answer - what is the twist weight - and dang, going to have to hunt down that funky movie now - I remember the ads

Also the ammo - does it show a rated speed, fps?
10" barrel, kind of short to be shooting the high(er) speed ammo

It is cheap reman ammo and there are no specs on the box other than bullet weight. The manufacturer doesn’t show this ammo on their site anymore either. I’m not mentioning the manufacturer yet because I haven’t reached out to them to get their feedback. They do have a 150 gr listed on their site that claims 1839 fps (barrel length not stated).

The Fiocchi ammo shows 1950 fps at the muzzle of a 16” barrel.

[bradbn4]

300 sort of has two modes - light weight and fast, heavy and slow - the heavy and slow should burn the powder in a short barrel, while the lighter weight bullets would be designed for high speed and longer barrels. I think there are two different twist rates - the heavy weight bullets I believe require faster spin rates than the lighter weight one. While I might have 1k in brass for the 300, I never did make a rifle to shoot that cal.

picked up from Foghorn

Nine inches of barrel will give you the perfect balance of light weight and velocity with the 300 BLK cartridge. It was designed to burn in short barrels and anything more is really just excess weight. The only real question is what twist rate to go with. Both AAC and Noveske use a 1:7 twist rate, while the PWS 300 BLK upper uses a 1:8 twist. The faster twist rate is perfect for the 220 grain ballistic monsters that subsonic 300 BLK ammunition use, but for the lighter hunting rounds (like Barnes? 110gr round) not so much. Those rounds like a slower twist, something closer to 1:10, but no one seems interested in making a barrel for that. PWS is as close as you can get right now. Even so, 1:7 isn?t terrible.

[Great-Kazoo]

thinking it is a mixture of a few things - but the bullet getting naked by tossing off the jacket seems part of the answer - what is the twist weight - and dang, going to have to hunt down that funky movie now - I remember the ads

Also the ammo - does it show a rated speed, fps?
10" barrel, kind of short to be shooting the high(er) speed ammo

I run 110 vmax, and up in my 10" blk not an issue.

[Honey Badger282.8]

This is my upper for those that are curious. It’s a 1:7 twist.
https://www.aeroprecisionusa.com/m4e1-threaded-complete-upper-10in-300blk-atlas-sone

[bradbn4]

Thanks 1/7 twist - might be too much for the cheap light weight ammo - tho what was referenced was not the 110 grain style or even the ultra light weight 78 grain ammo.

Hmm, got brass, got bullets, even one set of NOE 247 grain mold if I want to make my own bullets.

The Aero upper is sort of the direction I want to go, but with a 16" to reduce the stamp costs...thanks for that link.

Vmax is a good name in bullets...ok, I am out of ideas....

[Great-Kazoo]

Thanks 1/7 twist - might be too much for the cheap light weight ammo - tho what was referenced was not the 110 grain style or even the ultra light weight 78 grain ammo.

Hmm, got brass, got bullets, even one set of NOE 247 grain mold if I want to make my own bullets.

The Aero upper is sort of the direction I want to go, but with a 16" to reduce the stamp costs...thanks for that link.

Vmax is a good name in bullets...ok, I am out of ideas....

Do a SBA 3 brace and call it good. If you go with a 16" bbl, make sure you stay with the pistol length gas system. Read more issues with those not familiar with the 300 blk who ran a carbine gas system

[Honey Badger282.8]

Do a SBA 3 brace and call it good. If you go with a 16" bbl, make sure you stay with the pistol length gas system. Read more issues with those not familiar with the 300 blk who ran a carbine gas system

I’ve got the SBA3 brace and it’s awesome.

[brutal]

Do a SBA 3 brace and call it good. If you go with a 16" bbl, make sure you stay with the pistol length gas system. Read more issues with those not familiar with the 300 blk who ran a carbine gas system

I have a 16" DD 300BLK that's carbine length and runs flawlessly. As does my AAC 9".

[bradbn4]

If I would go with a brace I would embrace the tax stamps...one for the barrel and one for silencer. When I looked online last night for rifle barrels my budget was happy to find was out of stock.

I did spot a cheap barrel by Stoner; but too many posts with chamber issues at MidWayUSA. I was looking for a 1/7 twist rate, but that would be only needed(required) if I used the 247 grain setup from NOE.

[Honey Badger282.8]

Ballistic Advantage has 20% off for St. Patrick’s Day and has several still in stock.

10” 1:7 (barrel only, no gas block) for $132.
https://ballisticadvantage.com/10-inch-300-blackout-pistol-length-barrel-modern-series.html

[Great-Kazoo]

I have a 16" DD 300BLK that's carbine length and runs flawlessly. As does my AAC 9".

supers, subs or both?

[brutal]

supers, subs or both?

I don't recall running subs through the 16". To me, that doesn't make much sense for the cartridge. Supers, with and without a can.

I suppose I could try and see what it does.

9" eats anything of course, can or no can. I keep my DIY can on that one.

[Great-Kazoo]

I don't recall running subs through the 16". To me, that doesn't make much sense for the cartridge. Supers, with and without a can.

I suppose I could try and see what it does.

9" eats anything of course, can or no can. I keep my DIY can on that one.

Curious how the results are. Most 16" bbbls with carbine gas don't cycle, or perform well. Kind of like a first date ;)

[MarkCO]

Usually really thin jackets combined with sharp or too tight rifling .

Plated bullets are also well known for doing this .

Yep. Ripped up throat or gas port (not likely with a new barrel) or burrs in the rifling or gas port can also cause this (other than cheap ammo). Chamber a round or two next time you are at the range and pull them out and see if the jacket is getting cut on the feedramps, which we saw with a few 300BOs doing the same thing a few years ago.