How fast, and what weight, must a bullet run to stabilize in a 6 mm , 14 twist barrel?

[Randy Tidwell]

If it's there, I didn't see it. What case are you shooting?

I also have a three 6BRs, all 14 twist. One is a switch barrel XP 100. The attached photo is a target from the XP, 4 shots into .170" group. Had my figure on the trigger when I felt the gun move. Did my best to back off, hard to do with a 2oz trigger. Dern....

 

[woodnut]

Randy, don't jajust hate it when that happens? LOL
Ok, so I have loaded just a few rounds. Three each of : Varget, 39.5 gr, H4350, 44gr, and RL15, 38. gr. I looked in Hornady and Nosler books to give me a starting point using the 243 as a guide. Both cases are relatively close in capacity. I also left the seater out where I seat my 105s, so these 68 gr flat base HPT bullets don't have much holding them. I am shooting the 6 Creedmoor in a Ruger #1. I am hoping at 50 yds I can get the factory 105s to at least show me where POI is. The RL 15 loads are the back up sighters. But I will chrono all three loads. I should be somewhere between 3200 and 3400. When I finally get to the range, I'll report back.

 

[Randy Tidwell]

I don't think it will stabilize the 105s, you can barely stabilize them with a 9 twist.

I love No1s, been thinking about building a 20BR on a No1.

 

[woodnut]

Yeah, I doubt it, too. It's why I'm only trying it at 50.
I have a bolt rifle in 20 PPC that is crazy accurate and slings a 40 at over 3800! Having Bullberry Gunworks build me a TC Encore barrel in it. I do like your BR cartridge though!

 

[APDDSN0864]

Well, I leaped before I looked. I had a barrel rechambered before we knew the twist rate. Thought it was going to be either a 10 or 12 twist; but turned out to be a 14 ! I sure could use some input about what to run and how fast to stabilize it. My thoughts are 55 gr. at sizzling speed, or max out at 70 gr? Your thoughts?

Take a good look at Superformance and 55-70gr bullets.
I get 3,500fps + out of my 24" barrelled .243Win. with 75gr Speer TNTs.

Ed

 

[woodnut]

APDDSN0864, is your 243 a 14 twist? And yes, I will look into Superformance!

 

[Laguna Freak]

Well, I leaped before I looked. I had a barrel rechambered before we knew the twist rate. Thought it was going to be either a 10 or 12 twist; but turned out to be a 14 ! I sure could use some input about what to run and how fast to stabilize it. My thoughts are 55 gr. at sizzling speed, or max out at 70 gr? Your thoughts?

Forget the Berger stability calculator if you are shooting plastic tipped bullets. It will give you inaccurate results from its calculation which is limited to non-tipped bullets and it uses elevation/altitude to extrapolate air density. Use the JBM Ballistics stability calculator. It calculates variables for length of plastic tip, barometric pressure, and air temp. These variables are critical to bullet c.g. and gyroscopic energy/inertia , and air density.

JBM - Calculations - Stability

www.jbmballistics.com

 

[FEENIX]

use the Berger stability calculator

^^^This!^^^

 

[Hugnot]

Using the Miller stability estimator:

There are many bullets that would stabilize in a slow twist .243 like the 58 & 65 grain V-Max ® provided certain velocities are reached. Many of these short & light weight bullets have plastic tips. The Berger stability estimator does not make provisions for bullets having plastic tips. I would suggest going to the JBM stability calculator should you desire to use short & light weight 6mm bullets having plastic tips.

Another bullet not having a plastic tip is the 60 6mm Sierra hollow point varminter; I have used these against rodents for years before the advent of plastic tip bullets. Sierra makes a 55 grain plastic tip bullet, the 55 grain Blitz King ®. Running the Miller stability estimator again for the stubby light weight Sierra bullets:

The suggested Sg value needed to ensure stability is 1.4. I have found the Miller stability estimator to be conservative. The JBM estimator makes provisions for plastic tip bullets; plastic tip bullets appear to be your best solution for your 14 twist barrel.

The involved math is simple addition, subtraction, multiplication, division, except for some exponential stuff. A comparison for 30 caliber bullets is used - "=(30*H8)". The math appears on the top line. The JBM stability calculator should provide identical stability estimator values. JBM also has a list of bullet lengths. JBM has some plastic tip lengths but .14 inches is real close.

A comparison of the 70 grain Sierra Blitz King ® with the 55 Sierra Blitz King ®:

Looks like the 70 grain Sierra Blitz King ® is your best choice. The .008 shorter length of the 70 grain Sierra Blitz King ® compared to the longer & more pointy 65 grain V-Max ® allows for slower velocities to get Sg's over 1.39

 

[cape cove]

I have read in several articles that plastic tips don't have much of an effect on stability. I most certainly don't agree with this as I have had 2 different experiences with plastic tips and stability that lead me to think differently.. A few years back I had a 22/250 with a 14 twist. I thought I would be good for all bullets up to at least 55 grs. I purchased a box of Hornady 53 gr V-max, loaded and shot some. Right away I knew I was in trouble because the bullet holes were oval and accuracy was bad. I got in touch with Hornady and was told that a 14 twist may not stabilize this bullet. Having 80 bullets left and no other 224 rifle to shoot them in I decided to experiment with them. I cut the tips off taking them from .830 to .711 in length . No other change. I then proceed to shoot the same load. The bullet holes were nice and round and accuracy was .75 MOA. Not benchrest accuracy but decent none the less. The next experience I had was when a friend purchased some Barnes 168 LRX for his 9 twist 7mm Rem Mag, not realizing it required an 8 twist. They didn't work for him and he asked me if I wanted to try them in my 7/08. I loaded some up for my 9 1/4 twist 7mm/08. The load was 41 grs of H-380 WW primer in a RP case. Velocity was 2218 ft/sec and accuracy was non existent. The target looked like someone stood 10 feet in front and threw an handful of rocks at it. The holes were slots. I then proceeded to do as I had done with my 53 gr V-Max bullets only I did not have to cut them off. The blue tips pulled right out taking the bullets from 1.598 to 1.423. This was the only changer I made and the accuracy went from a pattern to one of the best groups I had ever shot with this rifle .340 . This is just my experience which led me to believe that plastic tips have a serious effect on stability and accuracy.

 

[woodnut]

cape cove, to follow your finds, I think that's why Hornady changed their bullets, or rather the tips. They were saying it melted(?) in flight and changed the BC. I didn't hear them say anything about accuracy though. Not exactly like your change, but I think it could be related ?

 

[woodnut]

Hugnot, Thank you very much for the Miller tables! I am looking at the 70gr. going 2700fps vs. a 55gr. going only 2550 and it give a higher Sg. of 1.50. I am trying out some flat based htp 68 gr. bullets that I think should be running ,according to two books, either 3200 or 3400 fps. They are .784 in length. I think they should be about a 1.40? If winds and rain go away, I'll get the try them one day probably next week.

 

[Jim’s Hunt]

Well, I leaped before I looked. I had a barrel rechambered before we knew the twist rate. Thought it was going to be either a 10 or 12 twist; but turned out to be a 14 ! I sure could use some input about what to run and how fast to stabilize it. My thoughts are 55 gr. at sizzling speed, or max out at 70 gr? Your thoughts?

I'm shooting 68gr out of a custom 6ppc with a 12 twist and a 65 & 70 out of a Ruger 6ppc

 

[Hugnot]

I have read in several articles that plastic tips don't have much of an effect on stability. I most certainly don't agree with this as I have had 2 different experiences with plastic tips and stability that lead me to think differently.. A few years back I had a 22/250 with a 14 twist. I thought I would be good for all bullets up to at least 55 grs. I purchased a box of Hornady 53 gr V-max, loaded and shot some. Right away I knew I was in trouble because the bullet holes were oval and accuracy was bad. I got in touch with Hornady and was told that a 14 twist may not stabilize this bullet. Having 80 bullets left and no other 224 rifle to shoot them in I decided to experiment with them. I cut the tips off taking them from .830 to .711 in length . No other change. I then proceed to shoot the same load. The bullet holes were nice and round and accuracy was .75 MOA. Not benchrest accuracy but decent none the less. The next experience I had was when a friend purchased some Barnes 168 LRX for his 9 twist 7mm Rem Mag, not realizing it required an 8 twist. They didn't work for him and he asked me if I wanted to try them in my 7/08. I loaded some up for my 9 1/4 twist 7mm/08. The load was 41 grs of H-380 WW primer in a RP case. Velocity was 2218 ft/sec and accuracy was non existent. The target looked like someone stood 10 feet in front and threw an handful of rocks at it. The holes were slots. I then proceeded to do as I had done with my 53 gr V-Max bullets only I did not have to cut them off. The blue tips pulled right out taking the bullets from 1.598 to 1.423. This was the only changer I made and the accuracy went from a pattern to one of the best groups I had ever shot with this rifle .340 . This is just my experience which led me to believe that plastic tips have a serious effect on stability and accuracy.

The little plastic tips do affect stability.

The formula op is "((92-C93)/C90)^2)) What this is: (( bullet length-tip length) / caliber) squared)).

Don Miller devised this method. https://en.wikipedia.org/wiki/Miller_twist_rule

The plastic tips are not weightless and some provision was needed to come up with a Sg (estimated) for the plastic tips.
https://arxiv.org/abs/1410.5737 , Michael Courteney

I use the 53 V-Max ® on rodents out of a 9 twist .223 loaded with CFE223 and it sort of shoots like a .22-.250, like many hits at 400 on small rodents.

But with a 14 twist:

An estimated Sg of 1.05 would sure make for "oval" (real bad) bullet holes. Not slower than 12 twist looks good for the .224 53 V-Max®.

I hope to shoot some deers with the 6.5 140 SST® from my old 6.5-.308 (pre .260) and needed to avoid oval bullet holes in Nov-Dec temps.