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Perfect Bullet Weight/Velocity Combination

 
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  #1  
Old 12-24-2003, 08:56 AM
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Perfect Bullet Weight/Velocity Combination

A question for a ballistics buff; Is there a perfect bullet weight for any given caliber? And given this weight, can you determine the optimum velocity it should leave the muzzel?
db
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  #2  
Old 12-24-2003, 10:06 AM
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Re: Perfect Bullet Weight/Velocity Combination

I've found kind of an answer to your question, but it's range dependant. My studies were wheich bullet shoots the flattest. Accuracy was not part of the calculations.

As you know there's a bullet weight/velocity tradeoff for each cartridge. A given cartridge can do a decent job maintaining the velocity until the bullet weight reaches a certain point and then it starts to drop off. Lengthening the barrel can stretch this out to heavier bullets, but the effect is still there.

For my own guns, and the programs I've run, here are a few basics for some standrad calibers that I have. All results are based upon standard rifle barrels, a 200 yard zero, and give the minimum drop at 400 yards:

.270 win - 130 grain
7mm Rem Mag - 150 grain, 120 grain was right next to it.
30-06 - about 165-175 grains (still need to study more)
.338 RUM - 185 - 200 grains.

As far as accuracy goes, my .270 likes 130 grain bullets the best, my 7 mag likes 150 grain bullets the best, and my .338 RUM likes 250 grain bullets the best. The 250 grain bullets have 2" more drop at 400 yards than the 200 grain bullets.

An interesting side note is that the .338 RUM shoots faster and flatter than the .300 RUM, even when shooting heavier bullets, and with less recoil! This begs the question, why would anyone EVER want a .300 RUM? Are the .30 caliber bullets that much better than the .338 bullets?

That's my $0.02, your mileage may vary.

Mark in Utah
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  #3  
Old 12-24-2003, 11:12 AM
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Re: Perfect Bullet Weight/Velocity Combination

HI dbhostler,

There are some bullets that are actually made for particular cartridges. For instance, the 155 Palma and the 175 SMK were both made specifically for the 308 win. It depends on twist as to what velocity is optimum.

The 178 AMAX is similar to the 175 yet it was designed for a magnum.

Belive it or not, my rifle (308) will match a calculator better with the 175 vs the 178 even though my rifle like the 178 better for accuracy from 100-1000 yards.

My theory is a bullet that performs with as close to .500 BC out of your particular rifle/velocity combo as possible, will give you the best all around performance as far as matching a ballistic calculator to 1k. Otherwise if its higher or lower, it will be 1 BC to 600 yards and another from 600-1000 yards.

Typically a 308 likes 150-175's

A 30-06 likes 165-190's

A 300 mag like 180-210's

A 7mm likes 120-150's

A 338 likes 225-300's

This does not meen that other bullets wont work well in these calibers, rather these are the most optimum for "most" applications. Velocity and twist make up a huge part in whats optimum.

The Sierra reloading manual has a whealth of info on which bullets were made for what as well as reloading info within each rifles capabilities.

To answer your question directly, the best way to determine what you want to know is to go to JBM ballistics web page and go to calculations, then go to bullet drag and twist. You must know your own twist and various bullet demensions. Enter the info and play with different bullet demensions until you get a stability factor of 1.5 within the velocity paramiters of your rifles capabilities. It will tell you the best twist for the bullet info entered and a stability factor for your entered twist.
www.eskimo.com/~jbm/ballistics/ballistics.html

[ 12-24-2003: Message edited by: meichele ]
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Originally Posted by Broz View Post
Please just answer one very simple question. Why would anyone shooting long range load a low BC , low SD 168 gr offering in a 300 win???????

My answer to this is. The only reason is to make the 7 RM look good. There is no other reason.

Jeff.
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  #4  
Old 12-24-2003, 11:34 AM
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Re: Perfect Bullet Weight/Velocity Combination

Michael
Don't you think throating has something to do with this, plus the quality of the bullets and powder compatability, quality brass, quality barrels, good gunsmithing, good bedding and worked out loads. For long range most people wouldn't use 130 to 150 gr bullets in the 7mm, or the 225s in the 338.

---Dan
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  #5  
Old 12-24-2003, 02:35 PM
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Re: Perfect Bullet Weight/Velocity Combination

DB,

When you said caliber, did you mean cartridge, or just that, caliber?

Caliber - No. Case capacity.

Cartridge - For LR work, yes.

Optimum velocity (accuracy?)- No. Grey area for sure.
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Brent Moffitt
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  #6  
Old 12-24-2003, 09:21 PM
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Re: Perfect Bullet Weight/Velocity Combination

Dan Conzo,

If a 300 win was throated for a 200 grain bullet but had a 13 twist, would you rather use 200 gain bullets or 165's?? Absolutly quality components are important and gun smithing ect.. But all the quality in the world wont help you if you try to use bullets made for one twist in the wrong one.

DB was asking what was optimum for each caliber. Years ago, the 308 was used mostly w/a 150 grain bullet. 150-168 just might be the most optimum, that doesent meen it has no LR capabilities. I know plenty of shooters that use 150's at LR w/a 7mm and 338 shooters that use 200's. DB wasent asking about which powder works best in a 24" tube vs a 30" tube. He didnt give a specific caliber/cartridge combo either. He mearly wanted to know if there is a most optimum bullet for each caliber.

Hopefully the gunsmith in question wouldnt throat a 300 win mag for 200's that had a 13 twist

If you throated a 300 for 190's in a 11 twist bbl, the 190 would be optimum for that particular rifle. What about in general?? Such as a factory rifle?
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Quote:
Originally Posted by Broz View Post
Please just answer one very simple question. Why would anyone shooting long range load a low BC , low SD 168 gr offering in a 300 win???????

My answer to this is. The only reason is to make the 7 RM look good. There is no other reason.

Jeff.
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  #7  
Old 12-24-2003, 10:30 PM
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Join Date: Dec 2001
Location: Nanty-Glo, Pennsylvania
Posts: 127
Re: Perfect Bullet Weight/Velocity Combination

Michael
I agree twist is paramount, I didn't include that because you already wrote that.
If a shooter is shooting long range, he has to figure the ballistic coefficient of the best quality bullets available which would give him the best advantage at those distances.
Most shooters wouldn't use a gunsmith that might not throat a barrel the way he wants it, or put on a barrel with the wrong twist for the bullet the shooter intends to use.
If shooters are using 150s for long range in the 7mm especially in the larger cases, they should look at the 162 Hornady AMAX, 168 Sierra MK and 180 Berger VLDs (If they have the proper twist and throating), they would probably do a lot better. If a shooter is using 200s in a 338, he might be better off with a large 300 case shooting 240s.
Factory barrels are a flip of a coin.

---Dan
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