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Military Guns and Ammunition

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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.

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PDW again   Small Arms <20mm

Started 20/12/20 by DavidPawley; 41196 views.
poliorcetes

From: poliorcetes

12/3/21

I would like to understand that aerodinamic issues: a really pointy bullet would not be so much different compared with a pitot tube on a mach 2 fighter...

Msg 7776.312 deleted
renatohm

From: renatohm

12/3/21

The Pitot tube isn't expected to keep its shape upon impact...

I seem to recall that pointy projectiles tend to break apart even at very shallow impact angles, which means that their usefulness may actually backfire if the impact angle isn't perfectly aligned.

EmericD

From: EmericD

13/3/21

poliorcetes said:

Looking that old 6.5 CT cutaway, I had a simple and possibly stupid idea: since bullet tip is totally surrounded by plastic case... why don't make it as pointy as possible, in order to improve slightly aerodinamics and armor penetration?

Depends of you definition of "as pointy as possible".

We tried bullets with "needle shape" ogive with Sears-Haack profile. They should be babied during the whole manufacturing process, babied during the packaging process, babied during the cartridge loading process, they don't bring any exterior ballistic advantage compared with bullets with a meplat of 0.8-1.2 mm, and the tip is so fragile that there is no terminal ballistics advantage.

If you can damage the bullet tip just by dropping the bullet on hard ground with an impact velocity of a few m/s, this tip will not bring you any advantage at impact velocity of several hundreds of m/s.

It's a known fact that the best penetration results are achieved with pretty blunt cores with a ballistic cap.

graylion

From: graylion

13/3/21

EmericD said:

If you can damage the bullet tip just by dropping the bullet on hard ground with an impact velocity of a few m/s, this tip will not bring you any advantage at impact velocity of several hundreds of m/s.

But the point @poliorcetes made was that the CT case protects against that. 

stancrist

From: stancrist

13/3/21

graylion said:

EmericD said: If you can damage the bullet tip just by dropping the bullet on hard ground with an impact velocity of a few m/s, this tip will not bring you any advantage at impact velocity of several hundreds of m/s.

But the point @poliorcetes made was that the CT case protects against that.

Even so, there are still the other issues noted by Emeric:  "They should be babied during the whole manufacturing process, babied during the packaging process, babied during the cartridge loading process, they don't bring any exterior ballistic advantage compared with bullets with a meplat of 0.8-1.2 mm, and the tip is so fragile that there is no terminal ballistics advantage."

poliorcetes

From: poliorcetes

13/3/21

Thanks as always, Emeric

However, I would like to insist a little bit: given that point is protected inside telescopic part of the case, a meplat decreased by an order of magnitude would not affect precision? given that some sport shooters do preciselly that... I mean, it's quite clear that conventional auto rifles don't use sharp-pointed bullets because if point is damaged during chamber insertion, grouping will be worsened

roguetechie

From: roguetechie

14/3/21

https://en.m.wikipedia.org/wiki/Meplat 

This was the term I was thinking of and in the wikinit clearly states that a correct meplat configuration can be consistently calculated that will give you your best supersonic performance.

You can go full smooth pointy but it will induce higher drag and etc. As I understand this you are essentially separating the boundary layer to keep more of the projectile out of direct contact and thus reduce aerodynamic resistance and velocity loss.

That and boat tail angle can and do have a pronounced effect on projectile performance.

And even you consider the fact that bullets just flat perform better terminally and more consistently the more velocity they have at impact v is squared in the relevant energy equation which means that additional velocity adds up way faster than adding weight to the projectile when it comes to your impact energy budget.

Hopefully this answers your question. 

Note: citation 6 in the wiki is the relevant NACA paper dealing with optimal meplat design.

roguetechie

From: roguetechie

14/3/21

There's also another issue though. Bringing something to a very incredibly sharp point will tend to result in a high Length to diameter ratio bullet that's light for a given L:D.

If you think about a case telescoped round and the way the nose caps for them work it also means that you must extend the nose cap back further resulting in less space for propellant because modern CT rounds aren't actually telescoped so your nose cap would have to extend back far enough to help stabilize the projectile from primer ignition until after it jumps through the freebore in the barrel throat.

graylion

From: graylion

14/3/21

This is the shape I am currently working with. I'd defo call that pointy enough. 6.5 mm, with a 3.5 mm penetrator. Bullet is 20mm long, might be possible to make longer with CTA

  • Edited 14 March 2021 4:20  by  graylion
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