Keyhole target hits

FALPhil · Posted: Mon Nov 19, 2007 9:52 pm Post subject: Re: Keyhole target hits

Welcome, Diesel!

I remember seeing keyholes while in the pits, too. One of the weaknesses of the Garand design was that there was no way to clean it from the breech end with a rod. Consequently, the muzzle end started reminding you of certain ladies around Subic Bay, and those jointed cleaning rods made from steel didn't help. As the wise man said, "Mr. Cleaning Rod is not your friend."

vint2 · Posted: Mon Nov 19, 2007 8:58 pm Post subject: Re: Keyhole target hits

Welcome aboard,Diesel! Pull up a stump , have a beer, and chat awhile!!
Vint2 Smile

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5946

Welcome to the forums Diesel! Howdy

Dimitri

diesel · Posted: Mon Nov 19, 2007 8:19 pm Post subject: Re: Keyhole target hits

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.

K.W. · Posted: Fri Oct 05, 2007 10:25 am Post subject: Re: Keyhole target hits

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.

K.W. · Posted: Fri Oct 05, 2007 10:21 am Post subject: Re: Keyhole target hits

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.

vint2 · Posted: Fri Oct 05, 2007 9:48 am Post subject: Re: Keyhole target hits

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

Deleted_User_2665 · Super Member Joined: May 06, 2006 Posts: 380

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

Long story..........................

FALPhil · Posted: Thu Oct 04, 2007 6:58 pm Post subject: Re: Keyhole target hits

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.

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5946

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

vint2 · Posted: Thu Oct 04, 2007 4:31 pm Post subject: Re: Keyhole target hits

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

gelandangan · Posted: Thu Oct 04, 2007 4:19 pm Post subject: Re: Keyhole target hits

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

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5946

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

Dimitri

FALPhil · Posted: Thu Oct 04, 2007 1:46 pm Post subject: Re: Keyhole target hits

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.

vint2 · Posted: Thu Oct 04, 2007 5:03 am Post subject: Re: Keyhole target hits

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