A few years back, I did some internet research (yea I know) about the best nose shape for flight in the transonic region. Most of what I found came from rocketry. Best i could tell, the parabolic nose was the recommended nose for this type flight, so I spent one summer playing with formulas til I got the parabolic nose shape I wanted. Sent the formula off to Rick to have him make one. Unfortunately he wasn't able too, so I wound up with an elliptical nose instead.
Still someday I'd like to get a mould with that nose shape I came up with to see what it did different from the elliptical and money noses I have.

The original postel nose shape works about as good as any in my rifles. The money bullet/redesigned Metford will shoot a little flatter , but not a lot. No matter the nose shape, I'm pretty firmly convinced that keeping the bullet length to just under what the twist will stabilize eliminates a lot of the unexplained odd shaped bullet strikes and dirt diggers, especially in a cross wind.

First off I have to say I don't think the nose shape matters enough in the transonic velocity range to out weigh accuracy. I also believe we are better served by a nose length that is 40 to 45% of the OAL and that that OAL is best if it's a tad short of what most twist calculations will tell you is maximum (like Don said). A long slender nose is not the best for BPCR velocity.

Brian,

A few years ago I was given a drawing and a bunch of numbers that came from someone working aerospace. The person who gave me the info asked if I could cut a mold to produce that bullet. I knew at a glance it wasn't going to be easy. After two attempts I had something that was close but not perfect, one minor flaw. I cast enough to do some testing for myself and turned the mold over to the guy that gave me the info.

He cast and shot enough to conclude it wasn't any better than a good elliptical, but was a lot lighter due to the nose shape. I came to the same conclusion with the ones I tested. It resembled a nose cone and was very pointed. I don't think it went anywhere after initial testing.

We need enough weight in the front half of our bullets to have the center of mass forward enough to keep things stable when the wind pushes hard against the nose. Move the center of mass too far back and things will become unstable in the quartering headwinds.

When doing some extensive research into the long pointed bullets so often mentioned in the Creedmoor days, the BBHC researcher sent me some fascinating info.
It was an article by WD Dodge about the efforts he went thru for the military and Winchester, trying to make the then new 30US a viable 1000 yard cartridge. The most telling part cane when he wrote that he finally decided to scale down the bullets he and others used with success in the 45 and 45 caliber creedmoor rifles.
Talk about nothing really new under the sun ?

(07-20-2021, 08:50 PM)Distant Thunder Wrote: He cast and shot enough to conclude it wasn't any better than a good elliptical, but was a lot lighter due to the nose shape. I came to the same conclusion with the ones I tested. It resembled a nose cone and was very pointed.

The thing about the parabolic formula, is, you can play with numbers til you get the shape you want.
Mine was not pointed, in fact the elliptical I got was much more pointed than the parabolic I wanted.
I can't post a picture of the nose, but can give you the formula if you want to see if you can print it out.

See if you can make heads or tails of this and print the shape:

f(x)=.225(x/.72)^.32

this is the other info I gave him:

"The Diameter would be .454 and the nose length would be somewhere close to .700 but I guess whereever it got to that width.
total length of the bullet would be 1.45 "

Bryan, is this the shape you were looking for ?

Brian,

Now I think you know where my math skills fall!

The little work I have ever done with anything parabolic doesn't help me much in understanding how that stuff works. The shape I cut in a mold for a friend who got the geometry from an aerospace guy was most definitely nosecone shaped and pointy enough that you would want to keep it away from young children who might need their eyes someday! If I have time to did up a bullet or a drawing and post it here.

If I remember correctly (and I often don't) I shot some at Lodi in a long range match and they did okay. I know my friend shot them in at least one match and while he was certain it would be the next big thing in BPTR bullets he didn't shoot it much after that first year so I'm thinking it shot about the same for him as it did for me, okay.

The problem I found with the nosecone bullet and even the prolate shape is the long, pointy nose really reduce the weight and in both of these shapes in an 18-twist they are likely to be under 500 grains in .45 caliber. That doesn't mean they won't shoot, they do, but most of us get a little squeamish with .45 caliber bullets under 490 grains when shooting at 1000 yards. You can go to a 16-twist barrel and get the weight up to "normal" for long range shooting or do what I did and move on to better shapes with decent weight and keep your 18-twist barrel.

It's always fun to play with "new" ideas in bullet design, but in the end it's difficult to improve on the older, proven designs. The biggest problem I have with the sharply pointed designs with long noses is that the last little bit out there on the tip isn't adding anything useful to the design. You still can only effectively stabilize up to a certain length and the little bit sticking out in front adds to that length. It does very little for the weight, it pushes the center of mass farther back toward the base, it moves the center of pressure more forward and does NOT offer any improvement in holding up to headwinds. It is mostly a negative feature, get rid of it!

If you cap your bullet's tip with a radius that is 30 to 35% of the caliber you turn all those negatives to positives and have a better bullet for the transonic zone in which we live. These are all facts that many either don't believe or choose to ignore. Everyone wants to shoot VLDs, but you can't!

Somewhere we have a disconnect between parabolic and those pointy elliptical, prolate, pointy rockets etc.
I'm gonna have to see if I can post a pic of the parabolic nose. It is not pointy.

(07-21-2021, 09:22 PM)Kurt Wrote: Bryan, is this the shape you were looking for ?

maybe close

Brian,

I'm sorry, I did not mean to say that your parabolic nose was pointy, I haven't seen it and I don't know. I did say, I have worked with a parabolic shape of some sort, but was as relates to dish antennas. That's the only experience I have with anything "parabolic". I just brought up the rocket nose cone bullet because you mentioned rocketry. The bullet I was talking about was the pointiest bullet design I believe I've ever seen. There are many rocket nose designs, the one I worked with in making a bullet mold was relatively new, updated and improved, but still a rocket nose.

This all show the problem i mentioned in my original post with trying to research transonic bullet designs, you usually end up with rockets or airplanes and not bullets. I have not found much written about the subject of bullet designs for transonic flight and our bullet spend the majority of their 3 second flight in the transonic zone. As was mentioned, it probably doesn't matter, but I find it interesting just the same.

I would be interested in see a picture of your parabolic bullet.