"Holey" Bullets Claimed to Go Faster

[HuskyNamedNala]

Take a look at the subject article:

http://www.gizmag.com/compbullets-faster-with-vents/20806/

According to the article an Italian weapons manufacturer has designed bullets with "holes" in them which reduces their drag, muzzle flash and improve bullet speed. They claim the holes allow the combusting gunpowder to "lubricate" the bullet within the barrel thus reducing friction and increasing exit velocity.

What do you guys think?

Personally, I call BS on the design. I can't say much about the physics inside the barrel, but I am confident that as the bullet travels through the air it will create cavity drag. See http://www.eng.uwo.ca/people/esavory/cavity.htm for an explanation.

The problem is that there will be a low pressure region behind the bullet, as well as where the holes are located (this would not be the case if the holes where placed on the top portion of the nose near the body), which might lead to pressure oscillations. I would think these oscillations might increase drag and increase the "noise" of the bullet. I can't tell 100% from the pictures, but it looks like the interior of the "holes" are not rounded to facilitate smoother flow to the rear of the bullet.

I am also thinking about longitudinal stability for the first picture shown. How fast does the bullet have to rotate to maintain a stable trajectory? Do these holes move the center of gravity too far forward? Will the drag of the holes increase windage (drag due to a spinning cylinder) and thereby reduce the angular momentum?

But then again, aerodynamics and fluid mechanics is still a black art for unknown designs. May be these holes really do make a difference?

 

[A.T.]

The problem is that there will be a low pressure region behind the bullet

Which is supposed to be less than with a normal bullet, so it outweighs the added drag at the sides? Is that what they mean by "rocket-like effect"?

 

[HuskyNamedNala]

I have no idea what they mean by rocket-like effect. That sentence actually makes no sense physically. If they mean that the combusting gasses can travel through the bullet as it exits the muzzle, then maybe it will reduce drag and provide some thrust for the first yard outside of the barrel. I think they may have used "rocket like effect" as buzz word.

What will normally happen is you will get recirculating motion behind the bullet because it is a bluff body (at least in the rear, in the front it is streamlined). The holes would dramatically reduce this recirculation if their entrance was on the nose (similar to the intake on a car, like my 2014 Dodge Challenger :) ), but since they are on the side of the bullet, they will actually be in a region of low pressure too. Imagine 2 vacuums sucking air out of a tank.

 

[DaveC426913]

Surely this is a simple matter to test, obviating any need to speculate (and risk being wrong).

 

[HuskyNamedNala]

Surely this is a simple matter to test, obviating any need to speculate (and risk being wrong).

I don't know about that. Say the bullet travels at Mach 1.2, you need a tunnel that can reach those speeds and a way to visualize the flow. CFD would be the cheapest option, but will require access to some serious computing power.

 

[rumborak]

Isn't it simply a question of shooting two bullets, one normal and one holey, and see which is faster? That's the claim after all.

 

[HuskyNamedNala]

That would be the easiest test, but it wouldn't necessarily back up their more detailed claims. You would need a high speed camera at the very least. Also, weight is a contributing factor to bullet speed and acceleration. The holes may simply make the bullet lighter and achieve a higher speed during the initial flight phase without the holes doing anything beneficial. So it would also make sense to test the bullets based on weight with identical levels of powder.

 

[rumborak]

Oh, the detailed "reasons" are just marketing fluff. I'm sure the ore they used for the bullets was first carried through the Appalachian mountains on organically fed Alpacas.

 

[A.T.]

The holes may simply make the bullet lighter and achieve a higher speed during the initial flight phase

Right, then you have to compare the ranges.

 

[A.T.]

Oh, the detailed "reasons" are just marketing fluff.

Well, we all know that speed holes make cars faster:

 

[DaveC426913]

Yeah, the detailed claims can be investigated IF the gross performance proves itself out.

"Hey look, it really does go farther, faster, more accurately! Let's find out how!"