Rifle Bullet Performance

fnuser · Posted: Thu Dec 10, 2009 8:02 pm Post subject: Re: Rifle Bullet Performance

I tried to add some comments to that quote but I was just going to say this load and deer are not mine I think you misunderstood, but the facts are good.

slimjim · Last edited by slimjim on Thu Dec 10, 2009 10:28 pm; edited 1 time in total

fnuser wrote:

twist was 1-10 but I think you are missing my point stability inside an animal is improbable to predict.

fnuser, thanks for the additional details. I ran the stability factor numbers for this bullet/cartridge combination. I assumed a cool day and 3100 fps velocity based on Barnes load data. I was surprised to see the resultant stability factor. The shorter TSX is just below the minimum recommended of 1.4 and the TTSX is really not stable enough. I'm amazed how much the small increase, 0.075 inches, in bullet length affects stability. The 100 gr .257 Tipped TSX really needs 1:9 twist or faster.

Caliber _ 0.257 Inches
Bullet Weight _ 100 Grains TSX
Bullet Length _ 1.113 Inches
Barrel Twist _ 10 Inches/turn
muzzle velocity _ 3100 fps
Temperature _ 45 degrees Fahrenheit (59 is standard)
Pressure _ 29.92 inches of mercury (29.92 is standard)

Stability Factor (Sg )= 1.37

Caliber _ 0.257 Inches
Bullet Weight _ 100 Grains Tipped TSX
Bullet Length _ 1.189 Inches
Barrel Twist _ 10 Inches/turn
muzzle velocity _ 3100 fps
Temperature _ 45 degrees Fahrenheit (59 is standard)
Pressure _ 29.92 inches of mercury (29.92 is standard)

Stability Factor (Sg )= 1.13

I'm can see your point that the terminal trajectory can not always be predicted. Based on the GSC experience, a stability factor 1.4 or greater is recommended if a hunter wants some predictability in how the bullet travels along its trajectory after impact. For the .25-06, a lighter (shorter) Barnes bullet would have higher stability

Pumpkinslinger · Posted: Thu Dec 10, 2009 10:27 pm Post subject: Re: Rifle Bullet Performance

Fnuser, great bullet picture, thanks! I understood that it was an exit wound and kinda figured it had hit some bone to slow it down.

Aloysius · Posted: Fri Dec 11, 2009 6:45 am Post subject: Re: Rifle Bullet Performance

1 thing is for sure: that bullet gave all its energy to the animal. I'm almost sure that deer didn't walk another step. And a clean kill with so little meatlosses, I call that good hunting and an excellent performance of the bullet.

fnuser · Posted: Fri Dec 11, 2009 8:37 am Post subject: Re: Rifle Bullet Performance

Slimjim just so I don't misunderstand what you are trying to say you are saying that if the twist was 1-9 it would not have become instable after hitting the skull and come out backwards?

chambered221 · Posted: Fri Dec 11, 2009 8:47 am Post subject: Re: Rifle Bullet Performance

I don’t find it surprising that the bullet did some endo’s along it’s path!!!
Take a look at a deer skull and the path that bullet took. No doubt in my mind that the possibility of a deflection could occur.
If we were talking about a 30 cal 180gr. Bullet (or bigger) I might see it differently.

Bottom line....dead deer !!!

slimjim · Posted: Fri Dec 11, 2009 10:19 am Post subject: Re: Rifle Bullet Performance

fnuser wrote:

Slimjim just so I don't misunderstand what you are trying to say you are saying that if the twist was 1-9 it would not have become instable after hitting the skull and come out backwards?

I'm only pointing out the lessons learned by GCS that faster spin rates make more stable bullets on impact. I don't know what would have happened in this situation if the spin rate was faster. I was surprised at the difference in the stability factor between these two bullets of the same weight.

fnuser · Posted: Sat Dec 12, 2009 9:11 am Post subject: Re: Rifle Bullet Performance

I guess, I'm pointing out that a bullet's stability is internal to itself and once it impacts anything substantial there is too much external force acting upon it for that to overide it which as chambered pointed out doesn't seem to matter. the importance of stability is in the flight.

slimjim · Posted: Sun Dec 13, 2009 8:58 pm Post subject: Re: Rifle Bullet Performance

I thought for a day on how to respond. fnuser, what you stated regarding stability is what most would agree is conventional wisdom - today's rule.

fnuser wrote:

once ... the bullet ... impacts anything substantial there is too much external force acting upon it for that to over-ride it which as chambered pointed out doesn't seem to matter. the importance of stability is in the flight.

GS Custom Bullets, with their experience with Africa's dangerous game with the need for predictable penetration as well as the harvesting of plenty of grazing animals of all sizes, has determined that faster twist rates can result in a more predictable bullet wound channel and less meat damage. They refer to this as the "new rule". To achieve this, however, the bullet the hunter uses must be able to maintain its integrity upon impact.

The .25-06 bullet you showed had enough spin to stabilize in flight but its stability factor needed to be significantly higher to follow GSC new rule. Most hunters with typical twist in today's rifles, would have to shoot lighter bullets at higher speeds to achieve the stability factor GCS is recommending (minimum of 1.4 and higher). It might be another 10 years of hunting with light monolithic bullets before many would agree the new rule is valid and replaces the rule that is prevalent today.

With the help of the discussions we have had, I feel like I'm understanding this new rule enough that I plan on trying to follow it the best I can. Consideration for bullet stability will be a prime factor in all my loads going forward.

Thanks again for everyone's comments.

Elvis · Posted: Mon Dec 14, 2009 8:49 pm Post subject: Re: Rifle Bullet Performance

man im amazed bullets stay together at all. just get out a calculator and work the rpms those puppies are doin. eg a 1 in 12 twist 1 revolution per foot traveled doing 3000fps is doing 3000x 60secounds=180000rpms no wonder a light jacketed pill blows up on impact I believe those rpm forces is what causes a mushroom and not just a splat.

chambered221 · Posted: Fri Dec 18, 2009 6:08 pm Post subject: Re: Rifle Bullet Performance

But most hunting bullets never go past the 100 yard mark..........therefor they usually only turn 300 revolutions or less !!! Viking

I know what your all thinking !!! Bonk

Ok....I'm out of here !!! Hiding

slimjim · Posted: Fri Dec 18, 2009 9:45 pm Post subject: Re: Rifle Bullet Performance

chambered221 wrote:

therefor they usually only turn 300 revolutions or less !!!

I like that perspective!