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Keyhole target hits
Discussion regarding the reloading of ammunition and tuning of loads for accuracy
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Pumpkinslinger
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PostPosted: Wed Oct 03, 2007 11:48 pm    Post subject: Re: Keyhole target hits Reply with quote

I don't think jacket thickness has anything to do with yaw or tumbling in the air or at impact. That's influenced by bullet shape, length and rotational speed. The 55 gr 5.56 NATO and the Russian 5.45 x 39 MM bullets are known for tumbling upon impact. A bullet has to be stable in the air in order to hit the target. Terminal performance is controlled by the bullet design and varies from "explosive", like the Barnes "Varmint Grenade", to straight through penetration, like the "solids" used for elephants, etc.

On that note: match bullets are designed to punch holes in paper, not for use on game where their performance will generally be erratic. I was amazed to see a website talking about shooting big game animals with match bullets and discussing that it took MULTIPLE hits to put the animals down every time. Apparently they couldn't understand that they were using the wrong bullets.

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Dimitri
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PostPosted: Thu Oct 04, 2007 4:23 am    Post subject: Re: Keyhole target hits Reply with quote

Jacket thickness doesn't effect its yaw on impact but instead if its going to fragment or not.

The 223 is known for yawing but its not actually the case, the majority of the wound potental of the round is because of the fact it fragments. The Russian rounds are ment to yaw in the traget however.

Dimitri

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vint2
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PostPosted: Thu Oct 04, 2007 5:03 am    Post subject: Re: Keyhole target hits Reply with quote

This is something we don't want in our gamegetters!!!!!

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FALPhil
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PostPosted: Thu Oct 04, 2007 1:46 pm    Post subject: Re: Keyhole target hits Reply with quote

Dimitri wrote:
Jacket thickness doesn't effect its yaw on impact but instead if its going to fragment or not.

Correct, but gyroscopic precession and center of gravity have a great effect on terminal ballistics. On the 7.62x39, the center of gravity is way aft, which causes it to do a "loop-the-loop" in a hydrostatic medium ending up with the heel pointed in the direction of flight after about 14 inches. IIRC, Dean Speir did a really good study in ballistic gelatin of this phenomenon.
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Dimitri
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PostPosted: Thu Oct 04, 2007 2:24 pm    Post subject: Re: Keyhole target hits Reply with quote

I think it works something like this might be wrong though not a expert on ballistics and hydrodynamics and the like here is my 2 cents. Laughing

On impact the rear (aft) part of the bullet has more mometum/energy then the forward lighter part, so as the bullet slows on impact the rear part carrying the energy of the bullet tends to keep pushing while the front part doesn't penetrate the target as easily, so the bullet begins to yaw so the rear part of the bullet becomes the forward part.

And on bullets that are ment to yaw even more like the Russian and British rounds with their air pockets the yaw (rotational) force of the bullet is much higher and will cause the bullets path to change in the direction of the yaw as well. Smile

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gelandangan
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PostPosted: Thu Oct 04, 2007 4:19 pm    Post subject: Re: Keyhole target hits Reply with quote

I shoot very long projectiles in my 300 whisper.. some up to a tad over 27mm (thats a tad over 1 inch Bushy Smile ) long.
If I shoot them at very low velocity (down to about 700fps) in my 1 in 7 twist barrel, I will see some (almost) keyholing effect on the target. if I shoot it faster, I never see any keyhole evidence.

Also, when I shoot a goat with the whisper, a lot of time I see pencil punch hole on the animal both on the entry and the exit hole, with hardly any tumbling of the bullet. Considering that the projectile move in low friction environment like air, and change in a split second to a very high viscosity material with very high friction coefficient (flesh), it seems that the projectile has been super stabilised in its flight path.

Based on the above, I think I could conclude that the spin of the bullet is a major factor in tumbling of the bullet.

my 2c

Gelan

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vint2
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PostPosted: Thu Oct 04, 2007 4:31 pm    Post subject: Re: Keyhole target hits Reply with quote

Seems this keyholing is a complex little demon, right?? Smile

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Dimitri
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PostPosted: Thu Oct 04, 2007 4:42 pm    Post subject: Re: Keyhole target hits Reply with quote

Gelan,

Your right rifle twist and the projectiles speed does play a role, consider a football (American Football) being thrown, if you do not put proper backspin compared to the speed your throwing it, on it it will not stabilize and fly "straight". So it will tumble in the air and keyhole if it was a bullet.

Tumbling in the animal after impact however isn't effected by that, as its yawing for different reasons. I'm thinking your Whisper isn't yawing in the target much if at all is because of the very low speeds its hitting the target, as if its a very low speed the bullet will not have enough energy to want to push the rear part of the bullet faster then the tip so it will just push ahead. Smile

Dimitri

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FALPhil
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PostPosted: Thu Oct 04, 2007 6:58 pm    Post subject: Re: Keyhole target hits Reply with quote

Just to be clear on terminology, yaw is a horizontal component, and pitch is a vertical component. Rotation is is referred to as roll. Precession is any change in direction of the axis of a rotating object.

A bullet fired from a rifled barrel is imparted roll. As it impacts a hydrostatic target, forces (all forces, including gravity, change in COG related to deformation, and displaced target medium) conspire to change the axis of rotation. In the case of bullets, which can be spinning at a rotational velocity of 20,000+ RPM, changes in the axis of rotation are referred to as "torque-induced precession", or what school children are taught as "gyroscopic precession".

None of this has much to do with bullets tumbling through the air before they reach the target, as typical animal tissue is 1000 times denser than air. Generally, bullets which tumble through the air do so because of an instability from the muzzle. This instability may be due to a number of causes: a COG which is not along the axis of rotation, insufficient imparted rotation, or some imbalance of forces as the projectile leaves the muzzle.

A very educational read on terminal ballistics is at www.rathcoombe.net/sci...ding.html. Every hunter would benefit from perusing the work there. An excellent primer on external ballistics is at www.exteriorballistics...index.cfm. It covers all the factors affecting bullets flying through the air.

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Deleted_User_2665
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PostPosted: Fri Oct 05, 2007 9:35 am    Post subject: Re: Keyhole target hits Reply with quote

I once hit a big 9pt with the nock end of the arrow.

Long story..........................
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vint2
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PostPosted: Fri Oct 05, 2007 9:48 am    Post subject: Re: Keyhole target hits Reply with quote

Was that a Gamegetter arrow???? I used to use 2417's for my Darton. Smile

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K.W.
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PostPosted: Fri Oct 05, 2007 10:21 am    Post subject: Re: Keyhole target hits Reply with quote

When I was loading silencer loads for 308Win 12"twist, 175gr bullets was keyholing. With 150gr bullets it is ok. Also my 22Hornet pistol and rifle 16" twist are keyholing with 55gr bullets. 50gr are ok.
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K.W.
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PostPosted: Fri Oct 05, 2007 10:25 am    Post subject: Re: Keyhole target hits Reply with quote

When I was loading silencer loads for 308Win 12"twist, 175gr bullets was keyholing. With 150gr bullets it is ok. Also my 22Hornet pistol and rifle 16" twist are keyholing with 55gr bullets. 50gr are ok.
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diesel
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PostPosted: Mon Nov 19, 2007 8:19 pm    Post subject: Re: Keyhole target hits Reply with quote

when I was in the pits pulling targets in the army over 50 years ago, all shootimg well worn M1's, left overs from WW2 and Korea, there were many keyholes at 100, 200, 300, and 500 yd's. so probably well wonn and negelcted bores will cause keyholing. diesel Oh, Ya, this is my FIRST post, just joined this board tonight.
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Dimitri
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PostPosted: Mon Nov 19, 2007 8:29 pm    Post subject: Re: Keyhole target hits Reply with quote

Welcome to the forums Diesel! Howdy

Dimitri

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