Rifle Bullet Performance

chambered221 · Posted: Fri Dec 04, 2009 8:41 pm Post subject: Re: Rifle Bullet Performance

tcknight wrote:

I can gain 300 to 400 fps more speed from my 75 grain .243 bullets from my custom made 1:12 twist barrell than from the standard 1:9.25 twist.

I run 55gr B-Tips in my 6mm Remington with a 1-10 twist and average speed is 4138fps.

wtf

You telling me if I switch to a 1-12 or better yet a 1-14 I can average 4538fps ??? Shocked

fnuser · Posted: Fri Dec 04, 2009 8:44 pm Post subject: Re: Rifle Bullet Performance

maybe not. don't you love to ask questions that you already know the answer.

chambered221 · Posted: Fri Dec 04, 2009 8:45 pm Post subject: Re: Rifle Bullet Performance

PaulS · Posted: Sat Dec 05, 2009 1:34 am Post subject: Re: Rifle Bullet Performance

I have always used more twist than the "book" says is required.
My 358 has 1:12 twist and I only shoot short bullets in it. 158 grain pistol bullets shoot sub-caliber groups and the 180 grain bullets shoot 5/8" groups.
I shoot 165 gr bullets in my '06s with 1/2 MOA groups or better.
I have never experienced "over stabilization" of any bullet and never spun one so fast that it came apart - including the pistol bullets that I shoot from the 24" rifle.
I have also always been a believer in the "bigger is better" school of thought when it comes to bullet weight and diameter. It is NOT a substitute for good shot placement and neither is any thing else. Shot placement comes first - then the biggest bullet that is reasonable is the best.
(22mm is about the right size for grizzly bear and 22 is about right for squirrels.)

Aloysius · Posted: Sat Dec 05, 2009 2:59 am Post subject: Re: Rifle Bullet Performance

Pardon me, but I've always been thinking that pushing a light bullet at high speed trough a fast twist makes the bullet strip. Result: a part of the jacket stays in the barrel (and will aid to ruin next shot) and the bullet itself has a sawteeth jacket with a flight nobody can predict or even worse: will be teared completely apart (due to high velocity and bad streamline)

PaulS · Posted: Sat Dec 05, 2009 3:58 am Post subject: Re: Rifle Bullet Performance

You know, there is a "Universal Law" called the "Law of Pragmatism".
It is defined as: "If it works then it must be true".
Sub-caliber groups with pistol bullets through a 24" rifle at 2700+ fps tells me that the bullets are intact when they reach the target.
I have never had anything but nice clean holes through the target with this load. I have always had groups that are smaller than .358" from center to center.
Does that sound like the bullet is coming apart to you?

Aloysius · Posted: Sat Dec 05, 2009 4:53 am Post subject: Re: Rifle Bullet Performance

Are you talking about a .358 Norma Magnum or a .358 Winchester?
A normal twist is 1:12" in the .358 NM and a normal speed for a 150 grs bullet is 3000-3400 fps...
and 1:12" is not a fast twist...
and maybe your pistol bullets have a hard and tick jacket?
and as always: some exeptions still can prove the rule Smile

Let's think extreme: what would happen when I put a +/- 70 grs jacketed bullet of a 32 ACP (7.65 Browning) on a well-loaded case of a .300 WM? When the .300 WM has a twist of 1:10" or 1:12", do you think you will find a bullethole somewhere?

slimjim · Posted: Sat Dec 05, 2009 7:40 am Post subject: Re: Rifle Bullet Performance

I have had fellow shooters experience a fast twist in a .223 resulting in lighter bullets coming apart and not reaching the target. However, GCS is not suggesting faster twists for copper-jacketed bullets. Monolithic copper or copper-alloy bullets have the integrity to spin at higher RPM. Shooters of GSC all-copper bullets have not experienced accuracy problems. I'm shooting 1/2 MOA groups with my .270 and 110gr Barnes TTSX with GSC recommended spin factor of 1.5. This is with a typical 1:10 twist. If I went to a longer bullet 130gr bullet they are suggesting that a 1:10 twist is marginal for stabilizing the bullet in flight and recommend a 1:8.5 twist for hunting or a 1:8 or tighter for shooting a bullet this long in close-in brush conditions.

.270 130gr bullet recommended twist

chambered221 · Posted: Sat Dec 05, 2009 8:09 am Post subject: Re: Rifle Bullet Performance

The construction of the bullet determines if it can handle a faster twist!!!
And yes there are bullets that can handle it, and some that can not.

Aloysius, Take a look at a Nosler reloading manual, they list their 180gr. Partition handgun bullet in the 358 Winchester, 35 Whelen, and 350 Remington mag data.

tcknight · Posted: Sat Dec 05, 2009 11:15 am Post subject: Re: Rifle Bullet Performance

chambered221 wrote:

tcknight wrote:

I can gain 300 to 400 fps more speed from my 75 grain .243 bullets from my custom made 1:12 twist barrell than from the standard 1:9.25 twist.

I run 55gr B-Tips in my 6mm Remington with a 1-10 twist and average speed is 4138fps.

wtf

You telling me if I switch to a 1-12 or better yet a 1-14 I can average 4538fps ??? Shocked

No. I'm saying that I was getting 3330 fps out of my .75 grain Hornady HP ammo with my factory 1:9.25 twist barrel.

I changed barrels and now my muzzle velocity averages 3620. As I said, there are many other variables, but twist had a role in allowing me to increase my muzzle velocity, lower chamber pressures, and increase accuracy (although precision hasn't been much better due to operator error Laughing

). Most changes caused by variables including powder selection, bullet selection, barrel length, twist rate, etc. are cumulative and can be additive if chosen correctly.

As you are aware (although the author I was addressing didn’t seem to be) 4,138 fps puts you at the top end of available speed for you bullet/caliber selection. You probably have no further room for powder, (100% load density) and all but the very best jacketed bullets will start to experience jacket separation at this twist and speed. Changing to a slower twist barrel would probably lower chamber pressures a bit, (but wouldn’t do you any good since you are maxed out in load density), gain you some accuracy, and allow you to shoot lighter jacketed bullets if desired. Accelerant capacity is your limiting factor now. Going to a .243 WSSM R may gain you another 100 fps.

tcknight · Posted: Sat Dec 05, 2009 11:20 am Post subject: Re: Rifle Bullet Performance

PaulS wrote:

You know, there is a "Universal Law" called the "Law of Pragmatism".
It is defined as: "If it works then it must be true".
Sub-caliber groups with pistol bullets through a 24" rifle at 2700+ fps tells me that the bullets are intact when they reach the target.
I have never had anything but nice clean holes through the target with this load. I have always had groups that are smaller than .358" from center to center.
Does that sound like the bullet is coming apart to you?

Apples to apples guys, apples to apples. 2,700 fps is not likely to make ANY bullet come apart. We are talking about much higher speeds here. Everything is relative, i.e. 2,700 fps + high twist + thick jacket bullet = not very likely to come apart but 4,000 fps + very high twist + thin jacket = not likely to make it to target intact.

chambered221 · Posted: Sat Dec 05, 2009 3:17 pm Post subject: Re: Rifle Bullet Performance

Lets back up a little !!! First I think you already know I was being just a little silly with you but that was for reasons of the discussion. I was hoping you would elaborate more on the differences of the two barrels.

But seriously now I‘m trying to figure out why you were not getting close to that to begin with. I’m assuming this is factory ammo because you don’t reload. If it were a matter of just the differences in the barrels you should have gotten rid of the old one a long time ago. But them again maybe you went from a 20 inch to a 30 inch !!!

As for my load I could probably get a little more because I’m just under max and the bullet is seated out more so than the book load data giving me a little more room there too. It’s not showing any pressure signs at this point and as you have seen in a previous post the load shoots pretty good. I think I’ll leave well enough alone.

And just for sakes of the discussion Nosler varmint B-Tips have been tested to well over 5,000fps. I however can't tell you what twist they were using in those test.

tcknight · Posted: Sat Dec 05, 2009 9:29 pm Post subject: Re: Rifle Bullet Performance

chambered221 wrote:

Lets back up a little !!! First I think you already know I was being just a little silly with you but that was for reasons of the discussion. I was hoping you would elaborate more on the differences of the two barrels.

.....

And just for sakes of the discussion Nosler varmint B-Tips have been tested to well over 5,000fps. I however can't tell you what twist they were using in those test.

Factory = 1:9.25" twist, 22"

Krieger = 1:12" twist, 23"

I found the difference in speed interesting too. One inch additional barrel length is not enough to explain the difference. Hey, proof's in the pudding! Very Happy

Hope ya know I was having a little fun with you too. Toothless

I can tell you what twist Nosler was NOT using. They were NOT using 1:7. Laughing

slimjim · Posted: Sun Dec 06, 2009 7:02 am Post subject: Re: Rifle Bullet Performance

Some interesting articles on twist rate.

Effects of Altitude and Temperature on Rifling Twist

Calculating Bullet RPM — Spin Rates and Stability

An increase in air density, e.g., very cold day, requires more spin to stabilize your bullet. Less dense air, e.g., hot day or higher altitude, requires less spin. Though benchrest shooters use slow twists for the best accuracy, articles suggest having more spin than you need in a hunting rifle is a beneficial. This is because a hunter encounters more variability from weather conditions to how clean the rifle is. No mention of faster spin rates having a significant affect on velocity.

slimjim · Posted: Sun Dec 06, 2009 7:27 am Post subject: Re: Rifle Bullet Performance

tcknight wrote:

Factory = 1:9.25" twist, 22"
Krieger = 1:12" twist, 23"

I ran your two situations through the stability equations in the second article above.

Caliber _ 0.243 Inches
Bullet Weight _ 75 Grains
Bullet Length _ 0.942 Inches
Barrel Twist _ 9.25 Inches/turn
muzzle velocity _ 3330 fps
Temperature _ 68 degrees Fahrenheit (59 is standard)
Pressure _ 29.92 inches of mercury (29.92 is standard)

Stability Factor (Sg) = 1.88

Caliber _ 0.243 Inches
Bullet Weight _ 75 Grains
Bullet Length _ 0.942 Inches
Barrel Twist _ 12 Inches/turn
muzzle velocity _ 3620 fps
Temperature _ 68 degrees Fahrenheit (59 is standard)
Pressure _ 29.92 inches of mercury (29.92 is standard)

Stability Factor (Sg)= 1.15

The calculator suggests that Sg shouldn't be less than 1.4. If Sg is greater than about 2.0, you may gain some accuracy by going to a slower twist barrel.

The data indicates that your new barrel with 75gr bullets is just barely stabilizing the bullet. This stability factor is less than benchrest shooters use. A lighter bullet like the 58gr V-Max may be a better balance with your new barrel

Caliber _ 0.243 Inches
Bullet Weight _ 58 Grains
Bullet Length _ 0.793 Inches
Barrel Twist _ 12 Inches/turn
muzzle velocity _ 3800 fps
Temperature _ 68 degrees Fahrenheit (59 is standard)
Pressure _ 29.92 inches of mercury (29.92 is standard)

Stability Factor (Sg) = 1.47