Berger Jacket Limitations with Velocity?

[Hugnot]

It's actually a function of bullet length and shape more than weight. In general yes, heavier bullets are longer and thus require a faster twist, but this isn't always the case. An example would be a 220gr round nose vs. a 168gr AMAX. The 220gr round nose will stabilize in a 1:14 twist but the 168 AMAX won't at the same velocity. Both bullets are the same length.

Looking at the Miller stability estimator using equal velocities:

Looking at the Miller stability estimator using load manual velocities for like a .30-06

The 168 AMax has a plastic tip and the Miller estimator treats this by subtracting it from the total length [ ((H9-H10)/H7)^2)) ] or giving the plastic tip no mass (weight) consideration. In this case the plastic tip does affect the Sg, by making the Sg calculator perform the AMax calculation using a shorter length. The shape of the bullet is changed by the plastic tip having no weight (like treated by calculation)..

Verification for above using accepted JBM calculations:

 

[brant89]

Looking at the Miller stability estimator using equal velocities:

View attachment 253329

Looking at the Miller stability estimator using load manual velocities for like a .30-06

View attachment 253331

The 168 AMax has a plastic tip and the Miller estimator treats this by subtracting it from the total length [ ((H9-H10)/H7)^2)) ] or giving the plastic tip no mass (weight) consideration. In this case the plastic tip does affect the Sg and changes the shape of the bullet.

Verification for above using accepted JBM calculations:

View attachment 253347View attachment 253348

Right, if you reduce the velocity of the 220gr by 400fps as you have in your example. Like I pointed out in my original post, I was comparing the two at the same velocity to be apples to apples. When trying to prove out the affects of a single variable you have to keep all other variables the same (unless you have access to DOE software which I do not).

 

[Hugnot]

The Miller estimator at the range with a 10 twist .22-.250:

This was when wifey had her 10 twist .22-.250 barrel. Her favorite load was a 40 Vmax with a full charge of RL15. Velocities were over 4000 fps. When I shot it I loaded the 68 grain Hornady HpBt with H4350 with velocities over 3200 fps. I never heard of the Miller stuff back then. On a warm, nice sultry day at 2500 ft. elevation shooting at the edge of the road that went thru the section center I could hit silhouette chickens placed in front of the fence on the section boundary - 880 yards. According the the Miller estimator this would not happen but it did. The Miller estimator is just that.

 

[brant89]

The Miller estimator at the range with a 10 twist .22-.250:

View attachment 253354

This was when wifey had her 10 twist .22-.250 barrel. Her favorite load was a 40 Vmax with a full charge of RL15. Velocities were over 4000 fps. When I shot it I loaded the 68 grain Hornady HpBt with H4350 with velocities over 3200 fps. I never heard of the Miller stuff back then. On a warm, nice sultry day at 2500 ft. elevation shooting at the edge of the road that went thru the section center I could hit silhouette chickens placed in front of the fence on the section boundary - 880 yards. According the the Miller estimator this would not happen but it did. The Miller estimator is just that.

I understand that it's just an estimate, but if you run the two 30 cal bullets I had mentioned at the same velocity you will see a difference that is likely well outside the margin of error. My original point was that it's length and shape that determine the required twist, not the weight. I think we can all agree on that.

 

[Bill28]

So I was out shooting LR with my buddy the other day. He was shooting a 6.5 STW pushing a 156 EOL at 3400fps with great accuracy. It was very intriguing to say the least. 16.5 MOA @ 1000 yards. It got me wondering, how fast can you really push them? And does the thinner jacket of the hunting bullet effect the maximum speed. Has anyone pushed a berger to the jacket failure limit? What were you velocities? And do you need to over twist the bullets to stabilize them at these speeds?

I'm shooting a .28 nos throated for the 195's with 1-8 twist. I push them at 3030fps pretty easy with N570. Now I'm curious about like a 175 @3300 or so. Just my brain churning a little bit. Curious to hear from people who have tinkered with this!!

With my 28 Nosler I'm shooting the Berger 180 vld's at 3250 with great results. Devastating on elk out to a 1000

 

[Huntnful]

With my 28 Nosler I'm shooting the Berger 180 vld's at 3250 with great results. Devastating on elk out to a 1000

Glad you mentioned this! I killed two bucks and a caribou with the 180's before I switched to the 195's. I just bought more 180 VLDs to see if I could get them to 3250 with N570. My old 180's were only going 3080fps.

 

[Hugnot]

Running the same pair but with a 168 having the plastic point removed gives:

Removal of the 168's plastic tip has reversed the Sg magnitude order resulting in the 168 having a higher estimated Sg than the 180, like the cut down 168 = 1.53 vs. 180 RN = 1.43 . The estimated Sg for a pointy 168 = 1.36. Apparently the calculation, [ ((C9-C10)/C7)^2)) ], (where C9 = length, C10 = tip length, C7 = caliber), provides a way for the plastic tip to affect the Sg estimate. The center of mass of the 168 should remain unchanged since the plastic tip is regarded as weightless. I would expect the center of pressure would be affected by the plastic tip or its removal.

It sure does look like bullet shape has an effect on Sg, at least estimated Sg

 

[Hugnot]

My ideas on bullet failure are that upon forming the ogive, bullet jacket metal is compressed to form a pointy bullet having a long ogive and during this compression and forming expansion fractures shown longitudinal cracks or zones of weakness are formed at right angles to the compressing force. This could occur in bullets having different jacket thicknesses. Thicker jacketed bullets would undergo more jacket compression and also have the same fractures.

Possibly gyroscopic precession might contribute to the failure. A long rapidly spinning bullet having some wobbling about its axis is slammed into air at high velocities.

I used to shoot the solid red tip .224 Hornady AMax bullets with great success. The new translucent red tip .224 ELDM bullets have replaced them. Shooting both types of bullets at 3150 to 3200 fps, no problems out of my 7.7 twist 5R, .22-250 - no gray smoke or sideways hits. Lots cheaper to shoot than a .243W and about the same results.

 

[Hugnot]

Sir Alfred's (Greenhill's) twist calculations vs Miller's

I compared a 140 grain .284 Sierra FB Pro Hunter (copper jacket, lead core -SG10.9), 1.12" long with one of my .284 Barnes 140 solid copper boat tail bullets (SG=8.79). 1.270" long. Stability indications or similar twists determined and used for both would produce good results. Possibly Sir Alfred's calculations would produce better results on top of the Scottish Highlands on a warm sultry day with the Sierra bullet. Reading up on Sir Alfred, I found that he was a smart guy.

 

[brant89]

Sir Alfred's (Greenhill's) twist calculations vs Miller's

View attachment 253558
I compared a 140 grain .284 Sierra FB Pro Hunter (copper jacket, lead core -SG10.9), 1.12" long with one of my .284 Barnes 140 solid copper boat tail bullets (SG=8.79). 1.270" long. Stability indications or similar twists determined and used for both would produce good results. Possibly Sir Alfred's calculations would produce better results on top of the Scottish Highlands on a warm sultry day with the Sierra bullet. Reading up on Sir Alfred, I found that he was a smart guy.

Note the faster twist requirement for the lower density material. I believe this is a function of the reduced rotational inertia due to reduced mass. If you use the same bullet but reduce the mass (as if you made it from a lighter material) stability goes down with a given twist. Basically, the more mass you have farther from the axis of rotation the more rotational inertia, and thus a more rigid axis of rotation.