Bullet Strength vs. Pressure--LASC Article and Lee Book in Contradiction?

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  • Last Post 09 January 2010
calinb posted this 22 July 2009

In Modern Reloading, Second Ed., Mr. Lee describes experiments where he proved that accuracy is lost very quickly when the ultimate compressive strength of a bullet is exceeded, due to high chamber pressure.  He claims that bullets should be cast such that their strength (hardness) is greater than the expected chamber pressure: “The best accuracy appears to be when the chamber pressure is close to, but does not exceed, the ultimate compressive strength of the bullet."

On http://www.lasc.us/TaylorBulletWeakEnough.htm,>http://www.lasc.us/TaylorBulletWeakEnough.htm, Ken Easterling appears to be advocating just the opposite--the yield strength of the alloy determines the MINIMUM, rather than maximum, pressure of the intended load.

Can anyone reconcile this apparent discrepancy for a newbie?

Thanks,

-Cal

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RicinYakima posted this 22 July 2009

Richard Lee's work is about leading the barrel, and loss of accuracy, with bullets sized at  barrel groove diameter, in an 03A3 rifle, with a huge throat. Taylor's is about bullet expansion when it hits animal flesh. They are talking about two different things. HTH, Ric

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calinb posted this 22 July 2009

Thanks much for the explanation! So for best terminal ballistics, we should select a casting alloy strength that's less than the chamber pressure, but for best accuracy (and perhaps less leading) we should select an alloy strength that's slightly greater than the chamber pressure?

It appears that optimal terminal performance and optimal accuracy are mutually exclusive!

I recall that Richard Lee said his findings were confirmed in a variety of other cartridges too, but he didn't elaborate in his book.

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RicinYakima posted this 22 July 2009

It is the complexities of cast bullet shooting than keeps us all working for “best” loads.

There is overlap but it is small and requires lots of load testing and development. This is for me the interesting part of cast bullets. You can also “trick” the alloy by making hollow point bullets or bullets that are softer on the nose and harder on the driving bands.

Lee's original pictures and a write up was done by Col. Harrison, NRA, and published in The American Rifleman in the early 1970's.

Ric

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LWesthoff posted this 22 July 2009

I'm not qualified to argue with either Lee or Easterling, but if the above quotes are accurate, I think they are talking about two different things. If I remember correctly, yield strength is the point at which plastic deformation starts. Ultimate strength is the point where total failure occurs.

 Wes

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CB posted this 22 July 2009

C

The LASC Range at Angeles Is the terraced level above our soon to be BR Range. I could throw a rock from our Range into their parking lot.

Stephen Perry

Angeles BR:fire

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LWesthoff posted this 22 July 2009

And now, students, you know what a “non sequiter"is.

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CB posted this 22 July 2009

L

You need to calculate the Modulus of Elasticity if you want to keep your Strength of Materials discussion going.

Stephen Perry

Angeles BR:fire

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calinb posted this 01 August 2009

Does anyone have a rule of thumb (that doesn't require calculating the modulus of elasticity ;)) for how much strength a gas check buys for you? (How much softer can the lead be with a gas check bullet without getting leading?)

Thanks,

-Cal

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cityboy posted this 01 August 2009

LWesthoff wrote: I'm not qualified to argue with either Lee or Easterling, but if the above quotes are accurate, I think they are talking about two different things. If I remember correctly, yield strength is the point at which plastic deformation starts. Ultimate strength is the point where total failure occurs.

Wes

You are correct.

Jim

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cityboy posted this 01 August 2009

Stephen Perry wrote: L

You need to calculate the Modulus of Elasticity if you want to keep your Strength of Materials discussion going.

Stephen Perry

Angeles BR:fire

The Modulus of Elasticity is basic property and is obtained from a tensile stress-strain test.

Jim

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Dicko posted this 22 December 2009

calinb wrote: Does anyone have a rule of thumb (that doesn't require calculating the modulus of elasticity ;)) for how much strength a gas check buys for you? (How much softer can the lead be with a gas check bullet without getting leading?)

Thanks,

-Cal

I know of no rule of thumb, but I can give you some empirical info.   To start with, gas checks get you no strength, they eliminate leading by their scraping action.  

Leading from plain base bullets also depends on hardness because friction is one factor in leading and a harder alloy reduces friction but only to a point.   Leading is minimal at 1350FPS with 6% Antimonial alloy.   In a 308 Win rifle I got zero leading at 1400FPS with 8%, and very slight at 1600FPS.   It was unacceptably heavy at 1800FPS.    Increasing the antimony content made little difference.  That's with plain base bullets.  

Basically, gas checked bullets do not lead at all because of the gas check.  I have no doubt that 6% alloy will not lead at over 2000FPS.   Maybe I should test it.   The reason for making bullets harder for high velocities is to avoid deformation under pressure because it degrades accuracy.   That's why best accuracy is found with hard bullets.   That's why, although 6% or 8% antimony will not lead with a gas check, 10% or more is the standard for cast rifle bullets except for hunting.

 

 

 

 

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CB posted this 09 January 2010

I must say that my experience and many of my friend's experiences differs with some of the statement made by Dicko above. I intend no disrespect, but I believe several of those statement are off base.

<"Leading from plain base bullets also depends on hardness because friction is one factor in leading and a harder alloy reduces friction but only to a point. That's with plain base bullets.” >

I have found that harder is not always, or even usually, better with plain base bullets. Going to a softer bullet will sometime cure a leading problem.

<"Basically, gas checked bullets do not lead at all because of the gas check.">

Gas checked bullets often lead especially if the bullet is undersized leading can be heavy, even with moderate velocity loads (under 1,600fps) Gas checks are not a cure all.

<"I have no doubt that 6% alloy will not lead at over 2000FPS. Maybe I should test it.">

Testing is always a good idea. You will find that any alloy may lead if improper bullet fit or too high velocity is present

<"That's why best accuracy is found with hard bullets.">

If this were true all CBA matches would be won by shooting heat treated wheel weights or other very hard bullets. Some of the best groups at our nationals are shot by plain base bullet shooters using very soft bullets. In many, but not all, situations a softer bullet will shoot better than a harder one.

Be wary of old and simple rules “that look logical” passed down as guidance.

John

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