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.308 / Berger VLD's of differing weights

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  #8  
Unread 02-13-2010, 09:11 AM
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Re: .308 / Berger VLD's of differning weights

Quote:
Originally Posted by bassin93 View Post
No offense dude but your post pretty much says that because they make a bullet in the calibre you want to shoot that it should be able to run at that speed in your cartridge just because it is the same calibre. Thats how people get hurt with that type of thinking. If that were the case, why would we need all the different cartridges

LOL... no, dude, it doesn't. It says that when I check the velocity required to stabilize the bullet that I have on hand, in a barrel with 1:12 twist, the velocity requirements are well outside of the maximums listed in 3 load data books (Nosler's manual, btw, has the hottest loads listed, by a good margin). Since lawyers have their inevitable say in the data that is published it's not much of a stretch to wonder how conservative the load data is and how far I can push it safely. Obviously 3,000 fps is not going to happen. Since Berger recommends a 1:11 twist or faster for their 210 grain bullet my 1:12 twist barrel probably won't shoot them well and even if it did there's not enough gain in energy and distance to pick the 210 grain bullet over the 190 grain bullet when loaded to safe velocities.
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  #9  
Unread 02-13-2010, 09:45 AM
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Re: .308 / Berger VLD's of differning weights

The 190 will be stable from a 1:12" even at .308 Winchester velocities (~2600 fps). What stability calculator are you running that suggests you need 3000 fps?

The 210 is the only bullet that won't work from your 1:12".

Cheers,
-Bryan
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  #10  
Unread 02-13-2010, 10:16 AM
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Re: .308 / Berger VLD's of differning weights

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Originally Posted by bsl135 View Post
The 190 will be stable from a 1:12" even at .308 Winchester velocities (~2600 fps). What stability calculator are you running that suggests you need 3000 fps?

The 210 is the only bullet that won't work from your 1:12".

Cheers,
-Bryan
Thanks for replying Bryan.

I'm using the analyzer/twist and stability module in Loadbase.

Here's the parameters that I used:

Bullet diameter: .308

Bullet Length:
1.375 (I mic'd a few of the bullets and they were all within .001 of this value

Bullet Weight:
190 gr

MV: 2,600 fps

Environment Conditions
29.92" Hg
59F
33% RH

Twist Rate:
1:12

Miller Method results: 1.35 Under Stabilized
Greenhill Method results: 1.49 Under Stabilized

At 2,900 fps the results change to:

Miller Method results: 1.40 Under Stabilized
Greenhill Method results: 1.49 Under Stabilized <-- didn't change

At 3,000 fps the results change to:

Miller Method results: 1.41 Under Stabilized
Greenhill Method results: 2.14 Fully Stabilized <-- Big jump


On a side note- without blowing myself up or damaging my firearm, I determined the max charge for IMR 4350 and the 190 gr VLD this morning. 48.5 grs has slight primer flattening but no other indicators. I'll back off 10% from there and work my way back up to a load that shoots well.
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  #11  
Unread 02-13-2010, 10:42 AM
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Re: .308 / Berger VLD's of differning weights

Mike,

The Miller formula is quite accurate, but sometimes the results get mis-interpreted.

In theory, SG only needs to be above 1.000 in order for the bullet to be stable. An SG of .999 or less is unstable, SG greater than 1.000 is stable. Because of the potential inherent error in the formula (up to ~10%) and because we shoot in a range of environmental conditions, we add a 'safety margin' to the SG so that we don't get close to 1.000. Some think that a margin of .3 is enough, and advise to keep the SG above 1.3 in nominal conditions so you don't dip down to 1.000. Others advise a safety margin as high as .5, and say you want the SG to be 1.5 or higher in nominal conditions so it doesn't dip down below 1.000. Personally, I advise a safety factor of .4, meaning you should aim for a stability factor of 1.4 in nominal conditions.

In other words, the label "under stabilized" that appears in the Loadbase calculation for SG's above 1.3 and 1.4 is very conservative. The only way the bullet won't actually be stable from a 1:12" twist is if there's more than 30% error in the Miller formula which is highly unlikely as 10% is likely to be the max error. If the calculated SG gets below 1.1, I'd start to worry that there might be a problem, but 1.3 and 1.4 is pretty safe.

I hope this discussion of the judgment calls involved in safety margins applied to SG helps to ease your mind about shooting the 190's from a 1:12" twist.

Take care,
-Bryan

PS, in your shooting this morning, did the 190's group well and make nice round holes?
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  #12  
Unread 02-13-2010, 11:51 AM
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Re: .308 / Berger VLD's of differing weights

Quote:
Originally Posted by bsl135 View Post
Mike,

The Miller formula is quite accurate, but sometimes the results get mis-interpreted.

In theory, SG only needs to be above 1.000 in order for the bullet to be stable. An SG of .999 or less is unstable, SG greater than 1.000 is stable. Because of the potential inherent error in the formula (up to ~10%) and because we shoot in a range of environmental conditions, we add a 'safety margin' to the SG so that we don't get close to 1.000. Some think that a margin of .3 is enough, and advise to keep the SG above 1.3 in nominal conditions so you don't dip down to 1.000. Others advise a safety margin as high as .5, and say you want the SG to be 1.5 or higher in nominal conditions so it doesn't dip down below 1.000. Personally, I advise a safety factor of .4, meaning you should aim for a stability factor of 1.4 in nominal conditions.

In other words, the label "under stabilized" that appears in the Loadbase calculation for SG's above 1.3 and 1.4 is very conservative. The only way the bullet won't actually be stable from a 1:12" twist is if there's more than 30% error in the Miller formula which is highly unlikely as 10% is likely to be the max error. If the calculated SG gets below 1.1, I'd start to worry that there might be a problem, but 1.3 and 1.4 is pretty safe.

I hope this discussion of the judgment calls involved in safety margins applied to SG helps to ease your mind about shooting the 190's from a 1:12" twist.

Take care,
-Bryan

PS, in your shooting this morning, did the 190's group well and make nice round holes?
Thanks for the clarification Bryan. I've seen similar info in your book and the LB help files however the "under stabilized" text in the program threw me off. I'll keep this post in mind in the future. My 3,000 fps comment resulted when I incremented up the mv value in the program until the program gave me a stabilized indication. I applied "if they sell them and they indicate that they'll work in my rifle then maybe 3,000 fps is possible" logic or illogic to the result. I asked "if" with no real plans to try to achieve 3,000 fps. The Nosler manual generally lists the most aggressive loads and they didn't come close to 3,000 fps for a 180 gr bullet. They don't even list a 190 gr bullet. The top of my box of 210 gr VLD is scratched so the recommended twist rate wasn't apparent. I went to the Berger site and found the twist rate there, which pretty much eliminated the 210 gr bullet from my tests.

I only made one round hole. My .308 has pretty good cold barrel manners so I was happy with the shot. I was looking for max load and the slightly flattened primer that I got was enough for me. The bolt was not stiff. The case did not grow (just resized it). All in all I think I'm being fairly conservative but this is MY test and I don't recommend anyone follow "internet advice" nor is this or any of my posts "advice". I've backed the max load value down to the load that I shot. The original max (my number not from a manual) was 50 gr's. My test shot was backed down from my selected max. For what it's worth I doubt if I could get 50 grains of 4350 in a .308 case. 48.5 was a compressed load with very little room.

Onward through the fog
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  #13  
Unread 02-13-2010, 12:32 PM
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Re: .308 / Berger VLD's of differning weights

For some of these powders, you need a drip tube to get enough into the case. W760 also needs around 50grs to bring performance above your normal .308win powders. Also, what brass are you using? I'm having good results with Winchester brass. I get over pressure with .7gr less in my rem cases and near that with federal cases. Am thinking about trying lapua and the new lapua with a small primer pocket .

-Oliver
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  #14  
Unread 02-13-2010, 06:46 PM
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Re: .308 / Berger VLD's of differing weights

I'm using nickle plated Remington brass. I have been pleasantly surprised with the Remington nickle plated brass I picked up a few months ago. I bought some for .308, 7mm Rem Mag, .223. and .270. I haven't tried .270 yet but the rest has been very consistent. I check neck concentricity and thickness on all of my new brass. I "cull" anything over .003 neck variation. Cull means, unless it's really bad, I use it for foulers and sighters. I've had very few culls. Less than 5 in a 100.
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