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I'm curious about the physical properties of soft-point hunting bullets in general. Specifically, I'd like to know what factors control the expansion of a particular bullet? Is it the strength of the copper jacket? Is it the hardness of the lead core? Is it a combination of the two? Is it...voodoo?!

Anyone who can answer, thanks a bunch. I'm really curious about it.
 

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For regular SP (not the controlled expansion stuff) I think different companies use different methods. I think jacket thickness is a big part of it and some bullets have jackets that are thinner on the nose than the base. But for the slower speed bullets like the 30-30 I would chance a guess that the alloy might be a bit softer too and more of it exposed.All of course speculation on my part and has got me thinking about it too .A Very Good question SOG I guess we all sorta take for granted the enginering and technical stuff that we shoot out our barrels.
 

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SP Bullet construction

Hey Ya'all,

There is a lot of information in loading manuals on bullet construction. Some have photos or cut-away drawings showing the inside of bullets of all sorts. Go to the Remington, Hornady, Nosler or other bullet websites and browse around. In general a round nose SP bullet has lots of exposed soft lead and a thin copper jacket, especially at the tip. Some bullets have a tapered jacket that folds back at impact then resists deformation more slowly as the bullet penetrates because the thicker taper is stronger and more resistant than at the nose of the bullet. Some makers actually bond the copper jacket to the lead core to keep the it from separating from the jacket.

Pointed SP bullets may have a thin, tapered, copper jacket up front with little slits that peel back quickly to start the mushroom then the thicker middle of the copper jacket regulates the amount of mushroom. The velocity of the bullet at impact is critical. Since manufacturers don't always know what cartridge will be used and how fast it will be going they make bullets that will mushroom on impact and hold their weight for generally good performance in a variety of conditions. Faster impact velocity and thicker game usually result in stubby mushroom bullets while slower bullets and light game will show a mushroom and longer shank. Some big game bullets are capable of penetrating completely through an animal, while some bullets are found in the hide on the far side of the animal.

It is hard to describe perfect bullet performance except in general terms. However, go the Barnes Bullets website to see a video of their all copper bullet penetrate a block of clear gel. You can actually see what happens inside of an animal. The bullet is also rotating at something near the twist rate of the rifle barrel. It rotates inside the gel block and would presumably do so inside the animal too. You will learn a lot by viewing different brands of bullets and reading what the manufacturer has to say in their advertising. Get a couple catalogs or view an on-line store for hundreds of offerings.

Cheers,

Squib
 
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