BHN and Velocity/Pressure

[fishnbob]

Is there a chart or table that gives you lead hardness numbers for certain velocities and/or pressure and if so, where can I find it? I just finished perusing Glen Fryxell book which is a thread here. Learned a lot but didn't see specific info. I am mainly interested in rifle data in .30 - .35 cal.

[Char-Gar]

There are so many factors involved, any chart you would find, would have limited value, if any.

[geargnasher]

http://www.lasc.us/TaylorBulletWeakEnough.htm

Do not take it as an absolute rule, but it's a pretty decent guideline.

Gear

[sqlbullet]

The lee manual has a similar chart that correlates each bhn to a psi. Again I find it a guidline, not a rule.

Each gun is different so their are guns that won't come close the the chart and some that will exceed the chart.

Also, fit is first.

[Reload3006]

I think memebr 357shooter has done a lot of testing he is shooting some soft Pb at mag velocities. IMO the more I have gotten into this I am finding Fit is the most important thing and velocity isn't as critical as I once thought.

[Marlin Junky]

There are so many factors involved, any chart you would find, would have limited value, if any.

Especially if you ignore internal barrel configuration. For example (assuming we are talking strictly about rifles and carbines) given any powder/boolit/velocity combination, the shallower the groove depth and/or the faster the twist, the harder the boolit needs to be. You can learn more with a bronze brush and your targets than you can by studying someone else's data.

MJ

[Larry Gibson]

Is there a chart or table that gives you lead hardness numbers for certain velocities and/or pressure and if so, where can I find it? I just finished perusing Glen Fryxell book which is a thread here. Learned a lot but didn't see specific info. I am mainly interested in rifle data in .30 - .35 cal.

Different burning rates of the powders used is what throws such "charts" off. 30,000 psi with Unique will have a more decidely adverse affect on a bullet than with the same psi with 2400. The same psi with 4895 will have less as will the same psi with H4831. The reason being is the accelleration rate is slower with the slower burning powders. Synominous with being punched vs shoved. Given a 30-30 with a 170 gr cast bullet of WWs + 2% tin; You will get a higher velocity with accuracy at higher psi with 2400 tan with Bullseye. Same with 4895 than with 2400.

Larry Gibson

[44man]

Different burning rates of the powders used is what throws such "charts" off. 30,000 psi with Unique will have a more decidely adverse affect on a bullet than with the same psi with 2400. The same psi with 4895 will have less as will the same psi with H4831. The reason being is the accelleration rate is slower with the slower burning powders. Synominous with being punched vs shoved. Given a 30-30 with a 170 gr cast bullet of WWs + 2% tin; You will get a higher velocity with accuracy at higher psi with 2400 tan with Bullseye. Same with 4895 than with 2400.

Larry Gibson
Well said Larry.

[williamwaco]

The "Official" rule is 1422xBNH = "the pressure". Some say it is the maximum pressure, others say it is the minimum pressure.

I am not really interested in that argument so will not offer an opionion.

Richard Lee publishes a chart that uses a formula of aproximately 1275xBNH.

At this location, you can find a chart using both formulas:


http://www.reloadingtips.com/reviews/lee_bnh_chart.htm




.

[Bret4207]

Not to throw another wrench in the mix, but Bhn only tells you part of the story. As I've noted before, I can produce 3 different Bhn from the same alloy or take 3 markedly different alloys and produce the same Bhn. Bhn is no more than a relative number. Trying to say a lead alloy at #bhn is only good for so many PSI or what ever is a waste of time IMO.

[45 2.1]

Not to throw another wrench in the mix, but Bhn only tells you part of the story. As I've noted before, I can produce 3 different Bhn from the same alloy or take 3 markedly different alloys and produce the same Bhn. Bhn is no more than a relative number. Trying to say a lead alloy at #bhn is only good for so many PSI or what ever is a waste of time IMO.

+1 Bret.................... Pick the right alloy and heat treat just so and you get results beyond what you believe is possible.

[geargnasher]

While I agree with everything above, I must point out something that may have been missed: For those boolit casters who haven't yet gained the experience that years of studying targets and playing with all aspects of the load gets you, taking Richard Lee's BHN equation and applying it to whatever scrap you can scrounge up is pretty reliable for building a decent shooting load in just about any gun. It really is.

I think it would be good advice for anyone shooting cast boolits to put what they think they know in a box for a while and do a workup for each gun they load for using at least two "reasonable" powder choices and the BHN/psi chart. I'll wager that it works as well at your house as it does in mine, and at least as well as at Richard Lee's, which is one of the unique advantages of his method. It's repeatable and fairly reliable across a large range of guns and reloaders. Although I certainly don't claim it's the way to develop the absolute BEST load in any gun, for the less experienced, it's a decent guideline to at least get them in the ballpark when starting out with shooting cast.

Of course fit, as always, is King.

Gear

[Mike Kerr]

Hmmm! Methinks a lot of this went over my head. I'll read it again next week.

regards,

:-)

[MtGun44]

Don't sweat it.

Mostly overthinking this, frankly. Hardness is definitely secondary. Get the other
things right and if there is some reason to still have a problem, especially with rifles,
then you can start adding a bit of hardness. It is probably more important in rifles,
but I am not a rifle expert, still learning. So far good results with moderate loads and
air cooled wwts in a few rifles.

For pistols, I have seen very little difference my self between good loads with 8 BHn
and the same boolit mold with water dropped wwts. Actually, I usually have had better
results with .357 and .44 mag with air cooled wwts which run about 11-14 Bhn. 8 Bhn
has been tested and not found to give any worse results with full power mag pistol loads.

http://castboolits.gunloads.com/picture.php?albumid=161&pictureid=929

I apologize to those that have see this pic before, but I consider it a good example of
how unimportant hardness by itself can be.

Bill

[pdawg_shooter]

Then there is the century old black art of paper patching. A correctly sized bullet, given a paper "jacket" to prevent distortion under acceleration, can be pushed to jacketed velocity with jacketed accuracy. No chance of leading the barrel, because the barrel never touches the barrel. The bullet exits concentric and stays that way.

[cajun shooter]

It is to be used as a reference only and I really don't think that the Lee book should have printed it without explaining how it maybe changed.
I think that the new book by Fryxell and Applegate From Ingot to Target explain it well when you read all the chapters.
As was posted there are not any charts that are 100% factual in that as we all know we have way too many variables starting with the gun used.
I will say that if the beginning caster wants to shoot a few of his lead bullets then he could start with a WW alloy and be close to safe and that is a maybe.

[Black Jaque Janaviac]

The reason being is the accelleration rate is slower with the slower burning powders.


I'm trying to wrap my brain around this one. I would think that 30,000 psi would produce the same accelleration regardless of burn rate. I though that the slower powders simply took longer to reach 30,000 psi and kept the pressure up there longer which is why the greater velocity.

See I would think that the bullet experiences the greatest amount of g-force when the pressure behind it is greatest. So just because a faster powder may reach 30,000 psi sooner doesn't mean the bullet is exposed to greater g-forces than a slower powder running the same pressures.

I thought what caused leading was the timing of these pressure peaks in relation to the bullets trip down the bore. 30,000 psi while the bullet is still in the forcing cone might allow gas blowby to begin. Whereas 30,000 psi after the bullet has sufficiently engraved and plugged the bore would produce no ill affects.

Likewise if the bullet is traveling XX fps before it engraves the rifling the forward momentum along with the lack of rotational moment can cause the bullet to shear off at the rifling. Whereas if the bullet is already rotating along with the rifling the lead might not shear off.

[Marlin Junky]

...I though that the slower powders simply took longer to reach 30,000 psi and kept the pressure up there longer which is why the greater velocity.

Yes, you are answering your own question... acceleration is a function of time and velocity (i.e., feet per second per second).

MJ

[Larry Gibson]

Black Jaque Janaviac

I'm trying to wrap my brain around this one. I would think that 30,000 psi would produce the same accelleration regardless of burn rate. I though that the slower powders simply took longer to reach 30,000 psi and kept the pressure up there longer which is why the greater velocity.

Has to do with inertial resistance to getting the bullet moving. Take a chunk of lead (simulated bullet) and lay it on the floor. Now smack it with a hammer to move it across the room. Note the damage done to the alloy. No lay a similar chunk on the florr and push it across the room. Note the lack of damage to the alloy. The object was moved across the same floor the same distance so it took the same "force" to move the chunk. However one damaged (unbalanced in the case of a bullet) the chunk and one didn't.

See I would think that the bullet experiences the greatest amount of g-force when the pressure behind it is greatest. So just because a faster powder may reach 30,000 psi sooner doesn't mean the bullet is exposed to greater g-forces than a slower powder running the same pressures.

Keeping the above example we know that a damaged and unbalanced bullet will not be accurate. Thus if the fast knock unbalances the bullet at 30,000 psi and the slow knock/shove doesn't then the slow knock/shove can push the bullet to a higher pressure/velocity before it unbalances the bullet.

I thought what caused leading was the timing of these pressure peaks in relation to the bullets trip down the bore. 30,000 psi while the bullet is still in the forcing cone might allow gas blowby to begin. Whereas 30,000 psi after the bullet has sufficiently engraved and plugged the bore would produce no ill affects.

There is some merit to that but it is not exactly that simple.

Likewise if the bullet is traveling XX fps before it engraves the rifling the forward momentum along with the lack of rotational moment can cause the bullet to shear off at the rifling. Whereas if the bullet is already rotating along with the rifling the lead might not shear off.

I think there is a misconception about rifling "shearing" off lead or bullets "stripping" in the rifling. Granted there can be some swaging of the land and groove engravements in bullets with long jumps to the leade. Many of us have driven cast bullets to extreme velocities without any evidence of the bullets "shearing" or "stripping".

Larry Gibson

[Black Jaque Janaviac]

Larry,

Thanks. This helps some. But. . .


Has to do with inertial resistance to getting the bullet moving. Take a chunk of lead (simulated bullet) and lay it on the floor. Now smack it with a hammer to move it across the room. Note the damage done to the alloy. No lay a similar chunk on the florr and push it across the room. Note the lack of damage to the alloy. The object was moved across the same floor the same distance so it took the same "force" to move the chunk. However one damaged (unbalanced in the case of a bullet) the chunk and one didn't.

OK. Except that in the case of your analogy you actually are not using the same force, the same energy perhaps, but not the same force. I see what you are saying though, there are two ways to achieve a given velocity - with less acceleration but over a longer duration and with more acceleration but a shorter duration. However, my question is a little different - we are talking the SAME acceleration but different duration periods which naturally results in differing velocities.


Many of us have driven cast bullets to extreme velocities without any evidence of the bullets "shearing" or "stripping".

The muzzle velocity doesn't predict whether the bullet will strip or shear. The acceleration, rifling pitch, bearing surface, along with groove depth and alloy strength dictate shearing. That said, the vast majority of any leading problems I've ever experienced were due to blowby of some sort.

[runfiverun]

think about pushing your truck.
once you get it moving any help keeping it moving makes it far easier than getting it started.
a whole football team running at it and hitting it at the start will get it moving too fast for you to run alongside and jump in.
and it will only move ahead a couple of feet.
they'll probably bash in your tailgate doing so too.
if you get it moving yourself and one of them comes and helps you push it, it gets easier.
the slow powder is like adding another player as each one gets tired, you can push it around the block at a full run this way.

black jaque:
your last bit there explains why fit is king and why twist rate of the Bbl matters too.
alloy strength is more lkely to survive,or be destroyed by the scenario above, but the slower powder and stronger alloy will produce better results when velocity is wanted.
notice i said stronger alloy not harder.

[Larry Gibson]

Black Jack

It takes the same amount of energy to move an object the same distance whether its moved fast or slow.

Also it is not "the SAME acceleration " because the accelleration is different. You are correct in "there are two ways to achieve a given velocity - with less acceleration but over a longer duration and with more acceleration but a shorter duration" which contradicts the next sentence. Both may "accellerate to the same velocity but the time/pressure curve of the slower burning powder will be slower than that of the faster burning powder. Basically, the velocity may end up the same but the accelleration of a slow burning powder will be longer than with a faster burning powder. If the developed psi is the same then the slower powder will also, most often, give a higher velocity.

I concure that improper fit to a degree is the leading cause of leading with a poor lube being second.

Larry Gibson