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-   -   Bullet characteristics (http://www.firearmstalk.com/forums/f30/bullet-characteristics-4415/)

redwheat 05-11-2008 01:53 PM

Bullet characteristics
 
I am interested in reloading for a 7 mm rem mag. What are the characteristics of the different bullet configurations? (boat tail, a-frame, plastic point, nosler, interbond) Does one fly straighter or farther, in general, than another? Please don't tell me that it depends on the powder load, because that is obvious. Is there a site that shows the different bullets and their shape? Thanks to all that can help.

1hole 05-12-2008 01:21 PM

Bullet designs change often so no one has attempted to compile a comprehenstve list of what's available. Even if someone did, it wouldn't be completely valid for long. Today, the old rules of thumb are best left to measuring thumbs. With modern bullets we just have to learn a bit about what's available and chose them according to our own needs.

For a given velocity, each bullet will "fly" on a trajectory determined by it's external shape, a measure of streamlining we call Ballistic Coefficent. You can find the B.C., etc., of most bullets from the maker's web site or their own loading manual.

If two bullets have the same B.C. and are launched at the same muzzle velocity, each will follow the same trajectory and resist wind deflection the same even if they are of different diameters (caliber) or weights.

Bullet point's (the ogive and meplat) contibute a lot to the B.C.; pointy things just don't lose velocity as fast as flat or round nosed things do. Point configurations such as hollow point, plastic tip, round nose, etc. are primarily designed for controlling the rate of expansion at impact but they can also increase the B.C. for flatter trajectory.

Boat tails increase the B.C. by making the bullet more streamlined but the boat tail only comes into effect after velocity has dropped below supersonic speed. For most game hunters, inside maybe 400 yards, boat tails have no meaning at all.

You will often hear of another bullet figure, Sectional Density. That is simply a ratio of bullet weight to diameter. At one time most bullets had much the same jacket and core composition so S.D. helped predict penetration, but not now. Vastly different shapes, weights and calibers may have identical S.D.s so it can be misleading.

IMHO, S.D. is now useless as a game bullet comparasion number. Regardless of the jacket or nose configuration, all bullets of the same diameter and same weight have the same S.D. but bullets with a high S.D. are still assumed to penetrate deeper. Not so. Today, depth of penetration is controlled much more by the jacket material and design, the hardness of the core itself and the nose design, than is S.D. A low S.D. solid copper game bullet from Barnes will drive deeper than a high S.D. varmit bullet from Hornady for instance.

Hollow points are usually assumed to rupture violently with impact, and that used to be true too, but not always. Today, most of the small caliber plastic tipped bullets have very thin jackets and do almost explode on contact, but other plastic tip versions are made for big game hunting and hold together very well.

Premium bullets like the A-frames, Partitions, bonded cores, etc. are nothing more than different ways to control jacket rupture on impact and keep the core in place for better penetration in big game. They work best, IMHO, in situations in which the cartridge is pushing the envelope, such as when using a 7 Mag. for brown bear. To learn if any such given high cost bullet will shoot accurately in YOUR rifle requires YOUR expermentation.

For me to tell you which big game bullet shoots or works best for me is likely to be misleading since you aren't going to be shooting my rifle. You need to learn how a bullet works for you, period. And understand that no point, core or jacket configuration will convert any game bullet into a grenade, nothing can assure you of instant kills.

Generally speaking, it used to be easier to make Hollow Points more consistant so they tended to be more accurate. That too has changed a lot. In factory rifles, today's plastic tips can often shoot as tight as H.P.s.

Because of all this, we must chose our bullets for the specific task we have in mind, not their point configuration, B.C. or S.D. There are NO shortcuts to learning and no certainties in predictions!

Catfish 05-17-2008 03:33 AM

1 Hole covered it all. The only thing left to consider is for what perpous do you intend to use the bullets? The liter bullets usually tend to have a thinner jacket and are intended for varmints. Heaver bullets tend to fall into 2 different catigories, game bullets and target bullets. Game bullets have jackets that are designed for proper expantion on game at the intended velosities the bullets will be shot at. Target bullet may or may not work well on game as they are intended for accuracy and that only.

1hole 05-17-2008 01:26 PM

Yeah Catfish! You expanded my last paragraph correctly. I just got writer's cramp and abbreviated it. :D


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