Is Hornady too optimistic about A-MAX stability ?

A

AlexF

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Hi, I'm looking at both 5.56mm 75 gr A-MAX and 6mm 105 gr A-MAX specs and Hornady seems very optimistic about bullet stability compared to other (Sierra and Berger).

According the 7th Ed Hornady Handbook of Cartrige Reloading the 5.56mm 75 gr A-MAX is stable in 1 in 9" twist and the 6mm 105 gr A-MAX will not stabilize in a 1 in 10" and slower twist. While Berger 5.56mm 75 gr VLD target needs 1 in 8" twist to stabilize and the 6mm 105 VLD target needs 1 in 8" to stabilize.

My question is this: do these 2 Hornady bullets stabilize in 1 in 9" twist in dense air (Canadian Winter -25C !) ?

Alex
 
This is a newer box and its listed right on the box 1-8 twist. The stability issues with this bullet are due to the OAL and not the weight... if you want to try something try the 75 Match they might work both the 69 SMK and 70 berger are much shorter then the 75 Amax
22792.jpg


This was a test I did with 80 Amax and a 1-12 twist barrel. As the bullet exited the barrel it began to tumble this bullet impacted the target at 10 feet it would have never made it to 100 yards.
keyhole.jpg
 
Super answer ! What about the 6mm 105 A-MAX Box ?

msg.drew said:
This is a newer box and its listed right on the box 1-8 twist. The stability issues with this bullet are due to the OAL and not the weight... if you want to try something try the 75 Match they might work both the 69 SMK and 70 berger are much shorter then the 75 Amax
22792.jpg
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Thanks, that's what I was looking for ! What about the 6mm 105 A-MAX Box ?
Alexandre
 
AlexF said:
Thanks, that's what I was looking for ! What about the 6mm 105 A-MAX Box ?
Alexandre
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On the old boxes before holograms which is about 2 years old now they where listed 1-9 Twist we do not have the new 105 Amax instock or I would have a picture of that too.

Shooters on the internet are reporting good results in 1-8 Twist...
 
With regard to the 105 grn amax. I was shooting them in my rem 9 and 1/18" twist in summer and getting sub 0.75" groups of 5 at 100 yards. I went out one cold winters day and they were shooting all over the place. Others have had no problems stabalizing them in the 9 twist. Powder was varget.
 
6mm A-max will stabilize in a 9.5 twist. I have not tried them in anything faster.
If given a choice, I would run an 8 twist in 6mm.
R.
 
If you can get the necessary dimensions, you can calculate stability at the Border Barrels site. I find the calculator quite accurate and it has predicted instability in one of my guns. The stability factor at the colder temperature came out between 0.98 and 1.03, and they were spraying right across the target.

Here is the calculator. Make sure you enter your twist of interest. When you do, then it displays two graphs. The lower one is stability factor vs velocity. Also be sure to enter your temperature of interest. Many make a big deal about velocity as a factor. It really isn't, and is quite minor. Temperature is much more significant.

Border Barrel Twist Form

You can use Berger's bullet specifications to check their calculation for twist, and see what stability factor they have at the recommended twist. All data is in this link, except for boat tail angle. I just assume 10 degrees.

Berger Bullet Specs

Don't know of a similar source of data from Hornady, and I don't shoot them, so no idea on dimensions.
 
Thanks for 105 answer

warrenb said:
With regard to the 105 grn amax. I was shooting them in my rem 9 and 1/18" twist in summer and getting sub 0.75" groups of 5 at 100 yards. I went out one cold winters day and they were shooting all over the place. Others have had no problems stabalizing them in the 9 twist. Powder was varget.
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Thanks Warren, your answer confirms what I expected: 105 gr A-MAX are borderline in 1 in 9 inch twist. They work very well when conditions are optimal but fail on border (extreme) cases.
I have a very accurate Remington 700 VTR in 243 Winchester and am looking for an explosive long range bullet for long range varminting. It needs to work a 100% of the time and I have very little patience for ammo which is flaky.

Alex
 
I just ran the stabilization numbers in Brian Litz's calculator for the 105g Amax and a 9 twist. Sure enough it shows the stabilization to be right around 1 in cold temps. (1 is the base number for stabilization, anything less like 0.99 will tumble. Brian recommends 1.4 as a "safe stabilization" number.)
 
I have shot the 75gr Amax out of 9 twist factory Savages out to a mile - no issues. BUT the Savage barrels may be a fast 9.

Heavy 6mm's prefer 8 twist.

Remember, twist rates listed from a gun manf may not be the twist you actually get in your barrel.

Jerry
 
dan belisle said:
I'd guess the loss of velocity from the cold is what dropped the bullet below it's stability threshold. Interesting. I use the 107 Hornady and Sierra a lot, but haven't experienced this (yet). - dan
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Actually no. If a bullet is stable at the muzzle it is stable down range. The forward velocity drops faster than the spin velocity, so stability goes up as speed goes down.

The cold air is dense so it provides more resistance. In almost all bullets the center of gravity is behind the center of the air resistance force. The higher the air resistance force the higher the net force there is trying to flip the bullet end for end.

I no longer trust the Miller formula for all bullet designs. It does not consider bullet shape, only weight and length.
 
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