Round nose, boat tailed bullets?

[44man]

Now that is something we all could use with the price of .22's. if we could just prime the brass.

[Digital Dan]

Some years back Federal made a large run of .22LR primed brass. I'm blessed to have rubbed shoulders with some of the wingnuts loading that stuff, some with BP. They shoot some very tiny groups.

[Traffer]

Those are some beautiful bullets. I have a couple questions for you. Is there a formula for, or have you calculated the effect of a hollow base on a shorter bullet. There are some folks here experimenting with bullets that look similar to the old musket minie balls. Some being used in pistols with no grease grooves and powder coated, give quite accurate results. I am curious about the potential of using the combination of no grooves with hollow base in a wider range of bullet applications. It would seem because of the weight being forward with a much lighter base -being hollow, aerodynamically they would be more stable. Maybe not at all at high velocities. I am sure you have a better understanding of these variables. What do you think?

Andy, no need to get lost here. Sit back and ponder a few things and maybe do a little doodling here. http://www.geoffrey-kolbe.com/drag.htm

and here: http://brooksmoulds.com/index.html

Ponder this: Bullet drag has 3 areas of focus from a design perspective. Nose, shank and base. Shank drag is typically in the 3% range, base is 7-15% and nose form accounts for the rest. The variability in base drag comes from both form (flat base/boat tail) and velocity (super and sub sonic). To develop the best form requires only that you define application. By that I mean velocity range. If you are considering low supersonic to subsonic velocities the simple solution is to look at forms used in the old days of BP arms, or perhaps more specifically, those used by long range BP shooters these days, such as the Money Bullet or variations of that theme. A flat base bullet exhibits better aerodynamic characteristics in the velocity realm you spoke of, pure and simple. The long radius nose with the round tip generates less drag and perhaps more significantly, reduced overturning moments re: spin stability because it is shorter than spitzer forms. It is a difficult task to argue with success. I note as well, that short range bench rest shooters tend to use flat base bullets too. I'm talking the 200 yard PPC crowd here.

Next on the agenda, once you settle on form, is weight. BC is a function of form and sectional density, the latter being a measure of weight to diameter. Same caliber, same form, the heavier bullet always wins the BC race. Question I'd pose on this topic, is how far do you plan to shoot?

Regarding the link to Brook's Moulds, if you are unable to find what you want anywhere else, you will not find anyone easier to deal with than Steve Brooks if having a custom mould made, nor will you find better quality. Equal perhaps, but not better. The bullets below are .30 caliber, 183.5 grains and intended for the very specific application of subsonic shooting with a suppressed rifle. The BC, calculated and observed is in the high .3 range with some measures suggesting about .390. I'm mildly skeptical of that, but cannot argue with the results on paper.



I use ALOX and a dusting of mica/graphite and the shallow grooves were intended for that purpose. They function quite well up to 1050 fps, that being the target velocity when the project was developed. A 50 yard target shot with a red dot sight:

[Ballistics in Scotland]

Andy, no need to get lost here. Sit back and ponder a few things and maybe do a little doodling here. http://www.geoffrey-kolbe.com/drag.htm

I've got Dr. Kolbe's book on ballistics, and it is extremely good without being mathematically turgid. As Border Barrels he does really excellent work. They aren't worth importing to a country with as many good barrelmakers as the US, but they seem to be as good as any.

[Digital Dan]

Traffer,

I think your take on hollow base styles is correct. Same theory is at play with Forster shotgun slugs and the old Minie bullets. Their weakness is found in vulnerability to anything other than mild pressure which leads to skirt blowout.

I've used some some cup base bullets for paper patch work and they suffer the same fate.

OTOH, if a gun will stabilize a jacketed bullet of X weight it will do so for X+ lead. If it will stabilize X bullet at 1200 fps it will handle X+ at subsonic velocity. Gyroscopic stability is a bit complex if one gets lost in the fine details but it generally isn't necessary to riddle that stuff too much. Don't over think it.

[andym79]

Okay, so this would be the best profile for a subsonic, transonic bullet if it were not for the fact that gas cutting would destroy the lead as the bore would not seal, i.e this would be sweet if it held together like a jacketed bullet does?



But lead being what lead is then this is the best compromise?
or is this the best compromise

The chart from the website seems to indicate that the second is!

That is loosely a NOE 311-230 FN
Is that about the sum of it?

Just to re confirm, so a boat tail would diminish accuracy in a cast bullet, unless you kept pressure very low, and even then a base that is not flat may lead to poorer accuracy because the bullet may not exit the muzzle square and true?

[eagle27]

You may take this for a cruel jest... But if you have a lathe, drill press or case trimmer which can be rigged to rotate the bullet at moderate speed on its true central axis, why not boat-tail flat based bullets with a pencil sharpener, or a device made to imitate one?

You do not speak in cruel jest, I do this very thing to turn a gas check shoulder on cast bullets for my 404J after they are thrown as plain base from my mould. Being a nose pour Hoch mould the bullets have a perfect base but I need a shoulder to take 44cal gas checks. Just replaced the handle on my RCBS bullet puller with a bolt and then set the puller die body in a three jaw chuck in a lathe. My die with a bullet inverted into the collet spins true and it is a simple matter to turn a shoulder or one could turn a boattail of any repeatable angle on bullets.
Weld a socket on a long tee handle to come in through the hollow lathe spindle and then it is a quick and simple matter to loosen the collet to take bullet after bullet without disturbing the die in the chuck. Works perfectly for me and I can put a gas check shoulder on a lot of bullets in an hour.

Viola!!

[andym79]

Sorry to bring this up again, but I am trying to confirm what profile is best to start off at say 1450-1600 fps and transition through the transonic!

Is a design like the money bullet great for subsonic flight, but a sharper spire type nose for transonic and supersonic flight?

I assume when traveling up through transonic you want spire as passing through mach 1 and for supersonic travel and when traveling down through a round nose for subsonic travel, therefore a compromise is half way between if you are not sustaining super sonic flight, is that correct?

These old videos whilst not about bullets help to explain it

https://www.youtube.com/watch?v=LSmqsg0DbTY
https://www.youtube.com/watch?v=bELu-if5ckU

I am not sure however that I am fully understanding it!

Shame I can't have a swept back bullet!!

[220]

Have you looked at the Lee 230gr .309, would be the cheapest boat tail mould I can think of.

[Digital Dan]

Andy, the Money Bullet is typically launched at velocities somewhat above Mach 1 and slows over long distance to subsonic. They hit things reliably at 1000 yards and more. There's a sign?

You're over thinking this. Go with what is a proven winner for that velocity realm.

[OS OK]

SNIPER 101 part 66 - External balistics, pressure and gravity...
[URL="https://www.youtube.com/watch?v=Z3h0pMQAFUU"] SNIPER 101 part 67 - Bullet Stability[URL]...
SNIPER 101 Part 68 - Bullet Balance Issues EXPLAINED! ... SNIPER 101 Part 69 - Bullet RPM & Overstabilization ... SNIPER 101 Part 70 - Aerodynamic Stability

I would watch these five short videos before making up your mind...they are jam packed full of all the considerations...

These are just a few from his website...TiborasaurusRex

Sorry fellas, I tried to add part 66 and screwed up the part 67 link but you'll see it listed there.