It seems to me most of you are going about this the wong way - you have the idea that somehow a “football bullet” would offer some advantage and then demand why it isn’t like that. The fact is that whatever advantage one might get out of it is miniscule and completely overwhelmed by the problems.
In other words, there’s no point.
My thought would be that a flat or concave rear end would catch the explosive gasses, deform the metal, and create a tighter seal with the barrel. A rounded rear would do the opposite, encouraging the gasses to flow around the bullet, reducing the pressure.
Also, remember that bullet size/weight is a critical part of the design, adding roundness to the back means reducing overall length to maintain the same weight. That reduction in length is also a reduction in bearing surface, which may not be a valued tradeoff.
I think Cheesie there has a good point.
Can’t have people being overly suppository in a bullet thread.
Here’s the thing, Blake. Any modification to a bullet affects the whole system. A bullet with a little tail fin added in back isn’t equivalent to the same bullet without the tail fin, it is equivalent to a slightly larger, more massive normally shaped bullet. The bullet with the tail fin is going to be a bit slower, a bit weaker, and bit less easily machined, a bit more expensive, a bit harder to seal, etc. A solid bullet is going to be a bit stronger, cheaper, faster, etc. No one variable rules all the others, but you have to consider the bullet as a whole system.
No real reason for it. The reduction in drag would be miniscule.
Also, I’m not fully familiar with it, but there’s apparently several factors that come into play when the bullet exists the muzzle. As in, right when the base of the bullet passes the crown of the muzzle, and propellant gasses can start escaping (usually at considerably higher speeds than the bullet itself) the shape of the base has a great deal to do with influencing the projectile’s flight.
As I said, I’m not up on this aspect, but I’m told that base shape- and consistency- has a large overall effect on accuracy.
Yup. Some of the very first “bullets”- as opposed to simple round lead balls- were hollow-based. The force of the gasses during firing expanded the “skirt” of the base into the rifling.
This allowed the muzzle-loader (they all were back then) to manage to get the bullet rammed into the bore, but the bullet could still get a firm engrave into the rifling when fired.
And Smiley has it on the nose- bullet shape has been extensively researched for over 200 years. Thousands of shapes, weights, materials, styles and forms have been tried. Some perform better in certain circumstances, some don’t.
The current style we see today- a lead core clad with a thin copper jacket- is the best combination of ease of production, cost, and performance.
Thanks for that Doc. Seemslike it basially coomes down to ‘it ain’t worth the effort’ and 'it stuffs up the exit characterisics.
Lemur866 I never mentioned tail fins.
Well, here’s my take. If a bullet is aerodynamic on both ends…the pressure that is supposed to propell the bullet is diminished. It’s not like a submarine…or an airplaine… A bullet has pressurized gasses in basically a vacuum moving it along. I think that the double aero-dynamic properties would work against the propulsion of it reducing force in any way I can think of.
Just to add a thought to Doc Nickel’s explanation – in addition to fully capturing the propulsion gasses and providing a slight expansion into the rifling, the flat end does not contribute to aerodynamic instability because of the speeds involved. A football or a submarine or a minivan move at a snail’s pace, but a bullet displaces air so fast that by the time the displacement has a chance to collapse, that collapse is well behind the path of the projectile and has no effect on trajectory.
Gairloch
Actually, a “football” shaped bullet does have an aerodynamic advantage, which is the reason for the boattail design. Why not a full taper? The slight advantage beyond a boattail gets lost in the noise along with the problem of a heavier bullet that demands more propellant combined with a longer projectile in the case which takes away space for propellant. The propellant gases have nothing to do with it. As mentioned, in the old days the gases helped seal the bullet by expanding it. Today, once the bullet gets past the forcing cone, it is sealed. Look at medium and large caliber projectiles. What makes the seal is not the steel bodied bullet but the very small copper, iron, and in some cases plastic rotating band. It doesn’t take much to make a gas tight seal.
Some projectiles today actually have a round (convex) base such as the 30mm Aden and a German 20mm X 81, I think it is, just to name two. Those are slower projectiles which gain a slight advantage because of it.
Another big reason is producibility. To make a football shaped bullet means more machining or more swaging, which means more material lost and/or more time involved in manufacturing, not to mention a few more QA points that have to be checked for a gain that is so negligible that it doesn’t justify the cost of manufacture, again coupled with the space being taken up for propellant.
Bottom line is, a football shape works and works well. There basically just isn’t much point to it when an easier made flat bottom projectile works ever so near as well. So why waste the time and money making them. A very few projectiles do better with a convex base than they do a flat base but those are mainly lower velocity projectiles that depend on stability because of their shaped charge fillings.
Thanks Turbo. Great post, answers the question perfectly, and even fills in a gap in my knoweldge: there are bullets with a tail.
I wouldn’t describe the nose as a parabola, because I’m 99% sure a parabola’s sides never approaches parallelism which is neccessary to avoid discontinuity into the rectangle/cylinder section of the bullet profile.
Rather as in foil sections of rudders and keels, The nose is comprised of one half of an ellipse.