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.308 Bullets Matrix Ballistics

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Re: .308 Bullets Matrix Ballistics

Postby Marauder 1 » Tue Mar 04, 2014 11:22 pm

They have some load data on there site, might give you a good starting point. They are definitely using some interesting powders.

Seeya
Mark
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Re: .308 Bullets Matrix Ballistics

Postby Marauder 1 » Tue Mar 04, 2014 11:51 pm

Image

Hmmm that appears to be pretty darn close to one or lower on a 10 to 1 twist rate. But their data doesn't tell you the test bed.

Image

On the other hand the 200 grain chart looks very promising.

Image

Hmmm I wonder how this one would shoot from a standard M28/30 or M28/76 the numbers look really good and it can be mag fed.

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Re: .308 Bullets Matrix Ballistics

Postby 0933 » Wed Mar 05, 2014 7:56 am

Grimstod wrote:You would need a 1:8 The stability factor would then be above 1.4SG

To bad its not a hallow point. That would allow use with 1:10 barrels.


Not necessarily...

The reason these bullets are have a higher B.C. is because they are monolithic. In a regular bullet, the majority of the weight comes from the lead core. These monolithic bullets have an average density which is less than a conventional bullet... which makes a longer bullet, which in turn yields a higher B.C.. Look at how long that 197 grain bullet is, 1.70".

With a longer bullet, your center of pressure is further forward of your center of gravity. Thus you have a longer arm for any force not acting directly through the cg. Longer arm means more torque... which needs a higher angular momentum to overcome.

That's why you need a higher twist rate... it doesn't have anything to do with the style of bullet, or even the composition. The length of the bullet, and velocity, dictate the twist required.

Here are some pretty good reads.

http://www.navweaps.com/index_tech/tech-043.htm

http://www.cfdthermo.tkk.fi/Teaching/Ku ... ields1.pdf

http://www.nennstiel-ruprecht.de/bullfly/fomo.htm

Angular Momentum

http://en.wikipedia.org/wiki/Angular_momentum

Also I would just add a short caveat about B.C. and the don millers twist rule. Take everything with a grain of salt... as those aren't hard and fast rules, they are merely comparing one bullet to a 'standard model'. That model doesn't necessarily have any relevance to the bullet being compared... that's why there's always 'ranges', or amended formula's.

That bullet may have a posted G1 B.C. of .8... but the G7 is probably in the low .3's. It is possible to get a G1 B.C. of .6 out of a .22 cal 55 grain bullet... BUT you need to drive it at 8,000 fps. Retarding G1 values are pretty much standard on any VLD bullet because the 'standard model' has no similarity to the bullet being compared.

Also, before you think that monolithic bullets are the end all bullet... check them out. They typically don't shoot well from conventional barrels. If you are planning on running monolithic bullets, you need a custom barrel, and resign yourself to the fact that you'll only shoot monolithic bullets from it... because conventional bullets don't shoot well from those barrels. This has a lot to do with the compress-ability factor between lead and copper, and the longer bearing surface of monolithic bullets.
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Re: .308 Bullets Matrix Ballistics

Postby Marauder 1 » Wed Mar 05, 2014 11:31 am

Good info T thanks, I figured if Ben was making a custom 32 inch barrel he might be looking at using this style of bullet.

I've been told by more than one source the Mosin Nagant LOVE bullets with long bearing surfaces, Finding conventional bullets with that design has become somewhat of a quest I must say.
Thanks again
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