Have we maxed out BC?

[Steve Blair]

A hallow base would not work. It would get crushed by the powder pushing it.

[br]
??? [br]
http://www.speer-bullets.com/ballistics/detail.aspx?id=220

 

[Laurie]

How would nose heavy hurt stability?
I would think that with nose heavy combined with hollow base, we could eliminate rifling all together.

Nose heavy bullets of the type that we shoot are less stable than those whose c of g is slightly behind the mid-point. Fact that can be read in any book on ballistics.

Do without rifling with a super-nose heavy bullet? What you're proposing is called a (crossbow) 'bolt' or 'quarrel', not exactly a new idea. The fact that when crossbows were replaced by early firearms, round balls and later early cylindrical body bullets were substituted for bolts tells you something. Even today's APDSFS tank cannon rounds use stabilising tail fins despite the enormous weight up front of a nose heavy depleted uranium penetrator projectile.

Bear in mind too how rifling and spin benefits were first discovered in the middle ages. Medieval crossbowmen found that if the crossbow stock was made with a curved track or developed such with wear and gave the bolt a bit of axial spin, its trajectory became more consistent. This lesson was later remembered as firearms were developed, although rifling created all sorts of problems in a muzzle-loading black-powder fuelled musket - basically the difficulties encountered in rodding a full-diameter bullet that would be gripped by the rifling down a fouled bore. The answer - related to another couple of posts above - was the hollow-base Minie bullet, undersize as loaded and whose rear end expanded under firing pressure to seal the bore and be gripped by the rifling.

 

[mikecr]

Nose heavy bullets of the type that we shoot are less stable than those whose c of g is slightly behind the mid-point. Fact that can be read in any book on ballistics.

I think you're wrong.

A rule of thumb with rockets(which there are many books written on) is to design in 'one-caliber stability'. That is Cp aft of Cg by one caliber, produces stable flight, whether using fins or any other method to achieve this.
In an extreme adjustment (opposite of modern bullets), where Cg is set forward, and Cp is 2cals or more behind, there is potential for weathercocking which would cause its flight path to veer into the wind(with rockets, and this is undesirable with rockets). And of coarse with any non-spin stabilized length that holds Cp ahead of Cg there is inherent instability.
This is why we're stuck with rifling -until we change bullet design.

I know of no bullets presently that are nose heavy. Nor do I know of any bullets that are base light. Until we cause Cp to move behind Cg we MUST spin stabilize.
But if we were to sharpen the base of pictured bullet, and load & fire it base first, it would be stable from a smooth bore:

 

[mikecr]

Another example,, pretend the hollow end here is the base instead of the nose.