Why is it called a "Boattail"?

[WSnyder]

The original work has serious issues with the quality of the prototypes and reproduction of the data. Last summer I worked with a couple of students and we found how bad the prototypes were. We then hired a local machine shop to make a batch of prototypes and they worked great.

This lead us to buying a HAAS CNC chucker lathe and using it for prototype testing. Since we did that, the results are stable and reproduceable.

It has been a very long road.

So it was solely a manufacturing limit design change rather than a performance driven change? Is the original design aerodynamically better than the revised design? I suspect the revised design would be easier to manufacture as a cup and core bullet down the road as well.

 

[HappyHellfire]

So it was solely a manufacturing limit design change rather than a performance driven change? Is the original design aerodynamically better than the revised design? I suspect the revised design would be easier to manufacture as a cup and core bullet down the road as well.

I can change the aerospike base to make it more aggressive but I wanted to start off with a very conservative design.

 

[WSnyder]

Or perhaps he won’t because I understand that ha “has reached his limit of suitable testers for his bullets”. Boy, I can’t wait to see these results. Someone please upload the popcorn emoji for my computer illiterate ass. lol.
Dave

Maybe this attitude that you have is why he chose two other shooters to test his bullets? It does come across pretty negative. I'm not sure that is your intention but that is how it appears.

 

[WSnyder]

I can change the aerospike base to make it more aggressive but I wanted to start off with a very conservative design.

So is the more aggressive design better? If so how much does it gain over the more conservative design? A guesstimation is fine as I assume you've modeled the performance of both.

 

[HappyHellfire]

So is the more aggressive design better? If so how much does it gain over the more conservative design? A guesstimation is fine as I assume you've modeled the performance of both.

I really don't like to talk about data until I have statistically significant numbers. If I can stabilize them, I expect that the drag curve will diverge sooner like at mach 2.4 (2700 fps) and stay lower till transonic.

 

[joshb]

I think it’s been tried.

AeroSpike Bullets

Looking for a little bit of advice and guidance here. I'm a ballistician and aerospace engineer with what I think is a cool new bullet design. I call it an AeroSpike bullet after the aerospike rocket engine that I got the idea from. Basically a lot of math to shape the base so that it lowers...

forum.accurateshooter.com

Thank you. Missed that one.

 

[Dave M.]

Maybe this attitude that you have is why he chose two other shooters to test his bullets? It does come across pretty negative. I'm not sure that is your intention but that is how it appears.

I started out very cordial and offered to be a Guinea pig for his bullets, but the more he posts and the less he answers questions and shares data that is in any way supportive of long range bullet accuracy. Now, I basically find it fairly entertaining.
Dave

 

[muleystalker]

I’m still waiting for an answer from the experts. Why not make a bullet with a pointed base? Maybe my first attempt sounded too much like a joke?
Serious thinking: I see in the pics that boat tail bullets still have drag inducing vortices. Wouldn’t a pointed base solve that problem?

Herters made one many years ago and used to sell them in their catalogue.

 

[divingin]

Good thing we don’t fire the bullets and the case goes with it….Ive never seen a less useful and more hilarious diagram.
Dave

I actually saw a box of 9mm ammo that showed a similar image. Not sure I'd trust ammo made by a company that didn't know how ammo worked.

 

[kris bassett]

Great drag chart here.

View attachment 1565246

That's the best one I've seen! Lol

 

[kris bassett]

I’m still waiting for an answer from the experts. Why not make a bullet with a pointed base? Maybe my first attempt sounded too much like a joke?
Serious thinking: I see in the pics that boat tail bullets still have drag inducing vortices. Wouldn’t a pointed base solve that problem?

I've read about people loading boattail bullets backwards with pretty good results. I can not recall where I read about it though?

 

[dellet]

I've read about people loading boattail bullets backwards with pretty good results. I can not recall where I read about it though?

Not uncommon shooting sub sonic for hunting before special purpose bullets were marketed.

 

[Coonman300]

I’ve heard of people reloading semi-wad cutters backwards in pistols for self defense purposes. Supposedly made them tumble and more damage in the victim. No idea if it’s true but interesting.

 

[rr2030]

I’ve heard of people reloading semi-wad cutters backwards in pistols for self defense purposes. Supposedly made them tumble and more damage in the victim. No idea if it’s true but interesting.

That was a thing we did in the 70's Speer 148 grain swagged hollow base wad cutters. Usually for snub nose 38's. I recall the lead was very soft. Cant vouch for the performance

 

[kris bassett]

I figured out who I read about doing it, it was Elmer Keith.

 

[HappyHellfire]

I’m still waiting for an answer from the experts. Why not make a bullet with a pointed base? Maybe my first attempt sounded too much like a joke?
Serious thinking: I see in the pics that boat tail bullets still have drag inducing vortices. Wouldn’t a pointed base solve that problem?

Ok, so I'll answer it but there is no way to answer without sounding like a big old nerd.

1. You are absolutely correct about the drag vortices behind the bullet. As best we can figure, about half or more of the drag on a supersonic bullet is due to this "base flow" phenomena.

2. If you have a water hose outside and you want to squirt the water further (increase the velocity) you put your thumb over the end and block part of the opening. The reduced area increases the velocity. Unfortunately, air that is going faster than the speed of sound behaves weird. To make it go faster you have to open up the area. This is the fundamental concept behind rocket nozzles.

3. Unlike with water, the "how" you open up the area is critical. Not any shape will do. We have spent a lot of time over the last 120 years working on the math of the "how". Just putting a pointy tip on the base to expand the air over won't work. BRL tried it in the 1960's.

4. This is the fundamental idea behind Aerospike Bullets. I designed a shape that allows the air to expand smoothly over the base to minimize the base flow.

5. Designing a bullet that is both "streamlined" for subsonic (pistol) and "isentropic" for supersonic (rife) is really hard. Turning the boattail around gives a pretty good "streamline" and is why the technique developed.

Hope this helps!
John S.

 

[Ledd Slinger]

Well we can discuss theories every which way til Sunday, but the only thing that really matters is the holes the bullets make on paper

 

[WSnyder]

Well we can discuss theories every which way til Sunday, but the only thing that really matters is the holes the bullets make on paper

Absolutely! He's got the capability to easily tweak his bullet to test for improvements. I would think the first design priority is to see if the drop/drift gains prove out. If so then accuracy improvements can be worked on if needed. It'll be another testing ball game when he switches to cup and core.

 

[joshb]

I like old nerds! Keep on truck in’!!!
“1. You are absolutely correct about the drag vortices behind the bullet. As best we can figure, about half or more of the drag on a supersonic bullet is due to this "base flow" phenomena.”
Thank you for that!

“BRL tried it in the 1960's”
Who’s that, why did he give up? Seems like the “holy grail” of ballistics! Solve it and you’ll make millions!

“Designing a bullet that is both "streamlined" for subsonic (pistol) and "isentropic"”

I would forget subsonic and focus on the other. Subsonic is a niche market and pistols don’t need it.

Forge on! I think you should work on the first design more, using a lead core type bullet.
This one , except I would mimic the nose shape for the base.

 

[WSnyder]

“BRL tried it in the 1960's”
Who’s that, why did he give up?

Ballistic Research Laboratory - Wikipedia

en.wikipedia.org

Where the well known Robert McCoy worked.