Hunting with a Marginally Stable Bullet

[RockyMtnMT]

Short answer: Marginal stability will greatly increase your chance of a bullet not opening or tumbling on impact.

Another short answer: A plastic tip does affect the bullet stability.

We have proven both in bullet impact testing. Low velocity impact testing proves that marginal stability makes a diff when we impacted at 1800 fps with marginal stability with no expansion, then impacted the same bullet at the same vel with full stability and had full expansion and shedding of the nose. Diff was 10" twist vs 7" twist.

We have tested plastic tipped bullets. In testing we developed the load with the bullet to be tipped, without a tip, because we had limited tips to work with, and had round holes and half moa targets at 100y. When the tip was added to the bullet, then accuracy went in the toilet with oblong holes appeared in the target. This was a very short, tiny tip and it put the stability past marginal to unstable. Turned out the new barrel we were testing with was a 7.375" twist, not the 7" that we had ordered.

 

[HARPERC]

Turned out the new barrel we were testing with was a 7.375" twist, not the 7" that we had ordered.

This is not uncommon even with quality custom barrels.

One of the reasons I'm not bashful about ordering a faster twist.

If we're marginal, and "tolerances" raise their heads the wheels fall off.

 

[Lou270]

Rely on what hornady states and not the calculator. The calculator ia just an approximation and does not comsider where the actual center of gravity of the bullet is. Hornady engineers have solvers that calculate the actual center of gravity and stability. The calculators are useful if you have no better way to check stability but at best they are an approximation. Goes both ways as well. The calculator may say you are stable but are not.

By the way I dont think the jbm calculator totally discounts the tip. I read the Miller paper a while back and created my own spreadsheet and while the berger version of calc is pessimistic, not counting tip at all is optimistic. I don't remember details but even plastic tip is included but at some reduced impact in the sg calculation.

Lou

 

[General RE LEE]

Rely on what hornady states and not the calculator. The calculator ia just an approximation and does not comsider where the actual center of gravity of the bullet is. Hornady engineers have solvers that calculate the actual center of gravity and stability. The calculators are useful if you have no better way to check stability but at best they are an approximation. Goes both ways as well. The calculator may say you are stable but are not.

By the way I dont think the jbm calculator totally discounts the tip. I read the Miller paper a while back and created my own spreadsheet and while the berger version of calc is pessimistic, not counting tip at all is optimistic. I don't remember details but even plastic tip is included but at some reduced impact in the sg calculation.

Lou

Hornady recommends 1:8.5 twist for the 175 ELD-X.

 

[ButterBean]

I'm working up a load for a 175 grain .284 ELD-X in a 1:9 twist Brux barrel in my 7mm STW.

Berger site has it marginally stable at 1.38 at my altitude and hunting temps. Load is for deer 500 yards or less.

What are y'all's thoughts?

Don't use it

 

[RockyMtnMT]

Hornady recommends 1:8.5 twist for the 175 ELD-X.

That would make it marginally stable and probably not a good idea if you are going to hunt with it.

 

[General RE LEE]

BTW I shot a 6" group at 600 yards today with it on steel. The Brux barrel is accurate.

Southern Precision Rifies aka Bug Holes told me the 1:9 twist would work with the 175 grain ELD-X.

 

[WAMBO]

I shoot the 175 ELD-X out of my 7mm Rem Mag 1-9" twist at 2935 fps.
Shot a Coues whitetail at 1025 yds DRT.
I think you'll be fine.

 

[L.Sherm]

BTW I shot a 6" group at 600 yards today with it on steel. The Brux barrel is accurate.

Southern Precision Rifies aka Bug Holes told me the 1:9 twist would work with the 175 grain ELD-X.

Shoot the **** thing and you'll be fine.

 

[yorke-1]

Will a marginally stabilized bullet work on game? Sure it will.

Will it work consistently and predictably? Probably not.

I shoot both the Sierra 183 SMK and the 180 SMK out of a 1:9" twist 7mm SAUM. Both bullets shoot well out to 1200 yards, even though Sierra recommends a 1:8" twist. If I put a piece of cardboard about 3' behind my target at 500 yards, the 183gr bullets will leave numerous holes in the second piece of cardboard that show the bullet has started tumbling. The 180gr SMK will show oblong holes in the second board when shot at 500 yards at a similar setup. Both bullets are accurate, but they're barely hanging onto their stability.

A tumbling bullet can and will do a ton of damage to something like a deer. You just can't predict what that damage will be every time.

 

[Lefty7mmstw]

You say 9" twist... what is your measurement of the twist? I'm tossing the 175 eld-x from a short throat 7rum at 2900 fps with a mild load of h50 bmg. I'm running around 1/2 moa with an 8" twist Brux that likes to destroy bullets. I can't run the 180 or 183 Sierra's or 180 Bergers in it as she'll destroy the bullets. The 175 interlock and 175 eld-x survive the barrel, so I'll shoot the barrel out with them and worry about other pills later.
The 175 eld-x seems to work well on mule deer from 300-500 yards from my 7rum. The last two years deer didn't ask for a refund.

 

[nralifer]

Short answer: Marginal stability will greatly increase your chance of a bullet not opening or tumbling on impact.

Another short answer: A plastic tip does affect the bullet stability.

We have proven both in bullet impact testing. Low velocity impact testing proves that marginal stability makes a diff when we impacted at 1800 fps with marginal stability with no expansion, then impacted the same bullet at the same vel with full stability and had full expansion and shedding of the nose. Diff was 10" twist vs 7" twist.

We have tested plastic tipped bullets. In testing we developed the load with the bullet to be tipped, without a tip, because we had limited tips to work with, and had round holes and half moa targets at 100y. When the tip was added to the bullet, then accuracy went in the toilet with oblong holes appeared in the target. This was a very short, tiny tip and it put the stability past marginal to unstable. Turned out the new barrel we were testing with was a 7.375" twist, not the 7" that we had ordered.

We agree with you that plastic tips can be problematic and that the bullet, to expand reliably at low impact velocity needs to be stable. We have observed in Barnes bullets, that if the tip is removed it aids in low speed expansion (<2000 fps) but when in place, low speed expansion is unreliable. We did not test for accuracy without the tip since the meplat size without the tip was considerably larger and would at least degrade the BC of those bullets even further. The various plastics available for tipping have low melting points, and when heated to about 800F will start to deform. 800F can be reached early in the flight of bullets driven at high MVs. Aluminum suffers none of those shortcomings

 

[RockyMtnUT]

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[General RE LEE]

Interesting enough that the 143 ELD-X going 3006 FPS from a 1:8 twist is 1.47 so technically marginally unstable.