Cutting Edge 143 MTAC doesn't stabilize in my 1:7.5 260 AI

[atl5029]

Today was the first time I have shot my hand loads with the 143 grain MTAC from Cutting Edge Bullets past 100 yards, and I have found that they are loosing stability by 200 yards when they appear to be stable at 100 yards. My rifle is a 260 AI with a 26" 1:7.5 twist barrel. My loads were clocking about 2900 FPS at the muzzle. At 100 yards they made perfect bullet holes in the target, but at 200 they are obviously keyholing. The CEB website says they need a 1:7.5 twist, but the description on MidwayUSA says 1:7, so I'm wondering if the original recommendation was a 1:7.

Does anyone else have experience with this bullet or the 140 MTH? I'd like to know if anyone has gotten them to stabilize or couldn't get them to stabilize, what your barrel twist is, and how fast you are running them.

That said, I think I'll be running the 130/133 MTH/MTAC instead now, so I have 1 box each of the 140 MTH and 143 MTAC I need to get rid of. If anyone wants them, let me know here and I'll send them to you. $114 for both boxes and I'll take care of shipping (that's the price on the CEB site. Not trying to make a profit on them here.) Act quick because I plan on returning them when I get back home after Thanksgiving on Monday.

 

[Darkker]

I'm a bit confused why you would use that bullet for those close distances in the first place, but that is another topic.

Even with an 8 twist @ 2,900 you have a stability factor of 1.33, so the twist isn't the issue. With the 1.501" length I'm wondering if it isn't more likely a CG/CP issue, or just not getting aligned in the bore correctly.

 

[atl5029]

I'm a bit confused why you would use that bullet for those close distances in the first place, but that is another topic.

Even with an 8 twist @ 2,900 you have a stability factor of 1.33, so the twist isn't the issue. With the 1.501" length I'm wondering if it isn't more likely a CG/CP issue, or just not getting aligned in the bore correctly.

I am just doing load development right now, but I intended to use the 140 MTH as a long range deer hunting load. Also if they were not alligned with the bore correctly, wouldn't i see tumbling/keyholing at 100 yards too? Also what do you mean by CG/CP issues?

Someone else on here has confirmed the 140 MTH doesn't stabilize in an 8 twist at well over 3000 fps. How did you calculate that stability factor. I've found that calculators I've used online for a certain bullet, twist, and MV say is should be stable, while the bullet manufacturer and reports from others say it needs to be a faster twist

 

[Darkker]

If the alignment is goofy, you can cause misalignment that could cause core/jacket slip issues. may not show up until beyond 100. Center of gravity Vs. Center of pressure. Causes a precession issue then tumbling.

The reason it isn't a simple matter of wrong twist rate is easy. Bullet velocity decays very quickly, relatively speaking. Rotational decay happens very slowly. So RELATIVE to the distance traveled, the bullets RPM increases with distance. This means you gain stability add the bullet travels, and where the term "going to sleep" comes from.
You have something else at play causing bullet upset.

JBM - Calculations - Stability

Twist Rate Stability Calculator | Berger Bullets

 

[toddc]

If the alignment is goofy, you can cause misalignment that could cause core/jacket slip issues. may not show up until beyond 100. Center of gravity Vs. Center of pressure. Causes a precession issue then tumbling.

The reason it isn't a simple matter of wrong twist rate is easy. Bullet velocity decays very quickly, relatively speaking. Rotational decay happens very slowly. So RELATIVE to the distance traveled, the bullets RPM increases with distance. This means you gain stability add the bullet travels, and where the term "going to sleep" comes from.
You have something else at play causing bullet upset.

JBM - Calculations - Stability

Twist Rate Stability Calculator | Berger Bullets

Pretty sure CEs are mono.

 

[Darkker]

Could be, I don't know anything about them other than the length. If the were soft, as all Barnes start out; that could be a culprit for damage during chambering/launch.

 

[atl5029]

If the alignment is goofy, you can cause misalignment that could cause core/jacket slip issues. may not show up until beyond 100. Center of gravity Vs. Center of pressure. Causes a precession issue then tumbling.

The reason it isn't a simple matter of wrong twist rate is easy. Bullet velocity decays very quickly, relatively speaking. Rotational decay happens very slowly. So RELATIVE to the distance traveled, the bullets RPM increases with distance. This means you gain stability add the bullet travels, and where the term "going to sleep" comes from.
You have something else at play causing bullet upset.

JBM - Calculations - Stability

Twist Rate Stability Calculator | Berger Bullets

I'll have to research the CG/CP issues. These bullets are solid lathe turned copper, so there is no jacket and core to separate.

 

[atl5029]

Could be, I don't know anything about them other than the length. If the were soft, as all Barnes start out; that could be a culprit for damage during chambering/launch.

the copper is very soft, but I don't think it is that either. Unfired rounds that have been chambered look fine. I have actually shot nice groups with this bullet at 100 yards. MOA or better with nice round bullet holes. Then at 200 yards they are very obviously keyholing. This makes me think my stability is marginal (which is what the Berger calculator says) and it has decayed enough to cause instability by 200 yards. No problems with 140 AMAX bullets in this gun either.

 

[bigngreen]

Man, you would think someone would at least Google search a bullet before giving advice on it!!

I've shot quite a few of the 140 MTH from a 8 twist at 5700 ft elevation and I'm right on the edge launching at 3200 fps, even a .3 less twist and they start wobbling. How far are you wanting to hunt with them?

 

[atl5029]

Man, you would think someone would at least Google search a bullet before giving advice on it!!

I've shot quite a few of the 140 MTH from a 8 twist at 5700 ft elevation and I'm right on the edge launching at 3200 fps, even a .3 less twist and they start wobbling. How far are you wanting to hunt with them?

I was hoping to take them out to 800-1000 for hunting. I ran the ballistics on their 130 grain going a little faster and it will get me out to where I want to be as well. I also know it will definitely be stable and extra velocity always helps with expansion.

Where I was shooting in PA yesterday was only 1154' in elevation, so if you're having trouble with them, I'm not surprised I'm going unstable here.

Only thing is now I have to develop a load really quick for these bullets before I go back to PA on 12/2.

 

[Mikecr]

If bullets make it past ~25yds without tumbling, they're at least stable enough to continue beyond.

 

[bigngreen]

I was hoping to take them out to 800-1000 for hunting. I ran the ballistics on their 130 grain going a little faster and it will get me out to where I want to be as well. I also know it will definitely be stable and extra velocity always helps with expansion.

Where I was shooting in PA yesterday was only 1154' in elevation, so if you're having trouble with them, I'm not surprised I'm going unstable here.

Only thing is now I have to develop a load really quick for these bullets before I go back to PA on 12/2.

I found 800 for me was the max range I would shoot game with the 140 at 3200 fps at 7500 ft elevation, very small wound channels and deflections one heavy hits. At 1000 yards on our test media they would not open when all other bullets would.
I had a conversation with them at SHOT last year and was told 800 yards was to far to hunt with that bullet and I needed a 300 or 338. There are multiple better longer range hunting bullets that are legit at those ranges in a 6.5, you'll have to run a lower BC than what they list as well.

 

[atl5029]

I found 800 for me was the max range I would shoot game with the 140 at 3200 fps at 7500 ft elevation, very small wound channels and deflections one heavy hits. At 1000 yards on our test media they would not open when all other bullets would.
I had a conversation with them at SHOT last year and was told 800 yards was to far to hunt with that bullet and I needed a 300 or 338. There are multiple better longer range hunting bullets that are legit at those ranges in a 6.5, you'll have to run a lower BC than what they list as well.

My estimate of a max range of 800-1000 yards came from their claim of a minimum impact velocity for max expansion of 1600 FPS. When I run the calculations in my ballistics calculator, the 140 at 2900 was reaching out past 900 before it dropped below 1600 FPS. The 130 needs to be pushed faster to reach that, obviously.

Why do you say I'll need to use a lower BC than what they list? How much lower?