Alloy pressure ?

[gunslinger20]

I just got a Lee lead test kit, in the chart it shows my alloy that tests 14.3 BHN strength at 20407 psi working pressure 18367 psi. The lead alloy calculator that I downloaded from this site lists lhe alloy mixture I put thgether as BHN 14 (very accurate chart to real world) I didnt mean to get long winded but all info was important, here is the problem: the estimated min peak pressure required for boolit obturation= 20242.the chart that came with the Lee sas: select a load with a chamber pressure not to exceed 4th colomn. Which is1836 on Lees chart



min pres on calculated ct. for obtuation 20242
-max pressure Lee ct - 18367 =1875

If it takes 20242 to obtuate how can max pressure in Lee cht be 18367 psi.

This isnt intended to be a brain teaser LOL

[white eagle]

maybe the difference lies in the 14.3 and the 14.0 you listed

[fecmech]

All I can say is I'm glad I don't let my boolits see that chart. That way they never know that they are not supposed to shoot that well! Seriously there are many loads that exceed that PSI with that BHN that are very accurate and with lead free bores.
.

[BABore]

Fun numbers to crunch and fret over, but meaningless in the real world. I have many very accurate loads that use plain based boolits of 10 bhn and lower running over 40,000 psi. Many others here do as well. Let your gun be the decision maker, not a chart.

[gunslinger20]

It doesnt make sense for the min obtuate pressure to be that much higher than the max working pressure.

[gunslinger20]

The reason I was kinda nit picking this cuz I was having some leading and am persueing all avenues. I just got a set of Lyman dies with the M die instead of the Lee FCD. Lee dies were swedging the boolits under size. M dies are not.

[Larry Gibson]

Lee's psi chart gives only a small bit of information. It works fairly well with many cast bullets because if you stay below the obturation psi the bullet will not get any uneven obturation to become very unbalanced in flight. This is why long pointy noses shoot well at the lower than obturation psi's and not above it. The time/pressure curve of the powder/load used also has a great effect on it. Use a fast burning powder and the accelleration peaks much faster than with a slower burning powder.

To push a cast bullet above the obturation level of the alloy an alloy that will obturate evenly is needed, a ductile alloy that is not brittle. A bullet design that fits the throat and lands is also needed. A long pointy nose is most often not good. If a bore rider the nose should "ride" the bore. The bullet should be as concentric to the bore when chambered as possible. As slow a burning powder should be used that gives consistent ignition while attaining the desired velocity is also needed to keep the psi as low as possible and the accelleration rate as slow as possible. Longer barrels with slower twist are better.

Lee's formula is proven but the use of that chart does not match up with reality as mentioned. BABore is correct; the gun and load will tell you more than the chart will.

Larry Gibson

[RobS]

I'm guessing you are shooting a handgun and in all reality if a person's bore is free of restrictions and/or providing the cylinder throats are larger than the bore (revolvers) then a person won't need obturation of a boolit. All this providing a person is using boolits that are coming from the cartridge case at the intended diameter, usually .001-.002 over the bore's diameter. I’ve made it a practice to load a dummy round of each group or set of boolits I cast and pull it to check the base for swage down. This simply eliminates one important variable should I run into issues. I've found the Lee chart to be of a reference but not inclusive to my reloading practices.

[gunslinger20]

Thats why I am now setting up a set of lyman dies as the Lee FCD was swedging the boolits.

[Doc Highwall]

LEE says to load to 90% of the obtuation pressure.
After that you are extruding the material like a spaghetti machine.
There are a lot of factors affecting the pressure that a lead bullet can take like what kind of rifling and how many lands and grooves along with the width of the lands to the grooves. Add to that how well the surface finish is and the diameter of the bullet is for the displacement of material from the rifling and the bullets shape.
Using a twist that is just fast enough to stabilize the bullet will help vs too fast of a twist causing striping of the lead.
Take the 22 caliber barrels as an example the twist rates go from 1:6.5" for 90 grain Sierra bullets to 1:16" for 22 Hornet with 40 grain bullets. The 1:12" and 1:14" are better for high velocity with cast bullets.

[Charlie Two Tracks]

I sure don't know everything about cast boolits but the guys here told me FIT is king. I had all this pressure stuff and alloy figuring going on but for me (and my revolver) it turned out that if I had the correct fit, I could use the same alloy for light and heavy loads. I can shoot wadcutters with 3 grains of Bullseye or 158 gr. RNFP with 16.3 grains of H-110 and still not have leading using wheel weights and 2% Tin. I'm sure there are many other alloys that would work also. I'm sure there is a post somewhere on this forum about the order of importance.