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Monday, 30 October 2017

Bullet Expansion by UPSET:

- Don't get upset now - if you take offence I'll have to build a gate eh ...😆

I guess that we all know what a "mushroomed" bullet looks like..

Mushroomed .223" Bonded Bullet.

- This is the expansion of the forward section of a fired bullet - when it decelerates on impact with a material.

- But what about the expansion or "UPSET" of the bullet's base as it accelerates from rest upon firing?

When a projectile is fired - the propellant gasses or 'muzzle blast' impact the base and cause it to accelerate and expand into the rifling of the barrel ... we know that - it's another familiar image:
BUT - those fired pills with the rifling grooves were contained by the gun's barrel for the period of forced acceleration while they 'obturated' .. have you ever wondered what might happen if that barrel restriction was removed?

Hornady 38 Special jacketed bullet fired from Revolver
with no barrel - has no rifling marks.

 - This "pregnant" looking projectile from 1976 was 'upset' by the force of the propellant gas "muzzle-blast" - but was not held to shape inside a barrel bore. The revolvers barrel had previously been removed.

Link to earlier background story about that fired round:
https://flicense.blogspot.co.nz/2017/01/bullet-sizes-diameters-v-bore-sizes.html

I guess that when you think about it - it's not really surprising that the initial force applied to a bullet's back-end is likely somewhat greater & more direct than that which causes it to 'mushroom' at the front as it impacts downrange.

Now .. there are lots of earlier interesting 'upset' images and details of experiments firing bullets from very short barrels - in this 1909 book "The Bullet's Flight".

- Dr. Mann establishes that a barrel longer than 10 inches is needed to completely prevent such upset expansion - and that the bullet's base is driven forward and starts expanding sideways before the main projectile's body and point starts accelerating.
BASES Expanded by 'Upset' Pressure As Bullet Leaves Very Short Barrel.
.32" Caliber bullets, Smokeless Powder, 1/- is unfired .. 2/- Fired from 5/8" (0.625") long barrel 12 gns powder .. 3/- Same with 15 gns. powder .. 4/- same again but 17.5 gns powder .. 5/- is front nose view .. 6 - rear view of base.

.32" Caliber rounds fired from varying very short length barrels, 5/16', 5/8", 2. 5/8"
( - excepting the top row shows a .32-40 case &
 bullets squashed by various weights between two steel plates.)

Franklin Mann was catching the fired rounds in  snow  and later, in oiled sawdust.

- So hollow-point nose technology is not the only way to expand bullets ..

- Now, imagine what dramatic video might be shot (110 years later) by an techie-expert with the latest ultra high speed cameras .. 'super-slow-motion' of such bullets emerging unrestrained from a short barrel test gun and growing in size as they're hammered from behind by the muzzle-blast powder/gasses - in full color .. WOW!

Dr. Franklin Mann concludes that lead becomes very plastic when subject to high pressure saying:

"When it is fully comprehended that a soft lead bullet, with a charge of powder behind, acts like a ball of putty in a popgun ..."

- Later in the book he further demonstrates that copper jacketed rounds driven by smokeless powder are setup in exactly the same way.

Marty K.


I can't tell you anything about this found image.
(Maybe after Major Earl Naramore - who worked with Hatcher?)


M.K.