Question for Bryan on bullet pointing

[hmcclannan]

I'm shooting a 284 Win with Berger 180 hybrids moly and pointed with a Whidden #1 die at 2800 fps. When you look at the bullet there is a definite angular discontinuity where the pointed tip meets the normal ogive. A friend who usually knows what he's talking about says this angular junction will cause an additional shock wave in flight with attendant degradation of ballistics. What do you think about this, and would a pointing system with a smoother transition give better results? Thanks.

 

[DocBII]

hmc,

It's never bothered any calibers I shoot, even when I accidentally overdid the pointing. They still shot higher than unpointed bullets.

HTH,
DocB

 

[boltman223]

I'm shooting a 284 Win with Berger 180 hybrids moly and pointed with a Whidden #1 die at 2800 fps. When you look at the bullet there is a definite angular discontinuity where the pointed tip meets the normal ogive. A friend who usually knows what he's talking about says this angular junction will cause an additional shock wave in flight with attendant degradation of ballistics. What do you think about this, and would a pointing system with a smoother transition give better results? Thanks.

You pointed them at 2800 fps? Wow, that's fast.

 

[Bryan Litz Ballistics]

I looked carefully at this when designing the pointing inserts for the Whidden pointing die. The short answer is, there is no difference in drag between the sharp corner and a smooth juncture in this case.

For more background, you can read up on Prandtle-Meyer expansion fans: http://en.wikipedia.org/wiki/Prandtl%E2%80%93Meyer_expansion_fan

In essence, a sharp convex corner doesn't actually create a single shock wave but rather an expansion fan. Regardless if the supersonic flow is turning around a convex corner or a convex radius, the energy required to expand the flow is practically equal, so the drag is practically equal.

The major thing you're doing when pointing bullet tips is reducing the blunt tip diameter. Everything else is details; and when you're looking at ~5% total effect, the details can be a waste of time to think about.

-Bryan