"I don't agree that the pressure difference (if any) can be attributed to the volume of the shot column."

This statement could not be more wrong , especially when dealing with loads that are close to max pressure . It can get dangerous really quick.

In the case of Victors' loads he increased the column height in the lead loads with 2 16ga ocs cards to make the load crimp well . Now take the same lead load with extra filler and substitute bismuth and have it tested and the pressure of that will be greater than the original bismuth load .

I doubt it -- show me some data to support your claim. IMHO The filler would change the pressure only because the entire payload is slightly heavier but the volume being greater due to filler has very little effect. It's the weight of the payload that makes the most difference.

Try just light weight filler and no shot at all -- put a bunch in, try different amounts -- you'll see very little difference.

Not trying to argue . There is plenty of data on the Hodgdon site you can compare for yourself .

Because Bismuth and Lead are close to the same density and hardness , as say Lead and steel . There may not be big difference , but there is difference . Enough difference that when you are shooting these loads in guns that require low pressure ammo it can easily put the load over pressure for said gun.



Better yet call the people that do the actual ballistic testing . I'm sure they can explain better than I can.

The next time you are not trying to argue you might try not starting the conversation with: "your statement could not be more wrong." That's a harsh and unsupported statement. At least you seem to have changed your position and are talking density and hardness now instead of length; which if you had read my original statement in context you would find that now you are agreeing with me. That's great--thank you!

Have a Happy Thanksgiving,

Ron

Ron , Certainly didn't mean to offend you . Just want everybody to stay safe. But I will stick to what I said , a taller or "longer" load column will increase pressure every time , more surface area friction in the hull .

Hope you and yours have a Happy Thanksgiving also.

Mark

Mark, I am sure your intentions are good -- but you are incorrect and spreading misinformation when you state that a longer load column (in and by itself) "will increase pressure every time." That statement is simply not true and can easily be refuted by this simple example: Take a known safe 12 gauge load with 1 1/8 oz of shot. Measure the length of the load column -- lets say it's 1" (for example, I didn't measure it). Some of the space in the hull is taken up by the plastic wad. Replace that plastic wad with a thin over powder wad and fill up the rest of the hull with a light weight material, like rice. That rice will be much lighter than the lead and the "load column" (the rice) will be much longer (maybe 2x longer) because you replaced the length of plastic wad with rice.

I guarantee you with 100% certainty that the longer yet lighter load column of rice will produce significantly less pressure than the shorter, heavier load column of lead.

It's the weight of the load column and to a lesser extent the compressibility of the payload that determines the pressure of a given powder charge. It has virtually nothing to do with the length of the payload. That's why Victor's comments are spot on:

"I tested the same load twice: one test with 1.25 oz of bismuth and one test with 1.25 oz of lead. All else the same. I was not surprised when the velocity and pressure data were essentially the same for both loads.

What’s heavier? 1.25 oz of bismuth or 1.25 oz lead?"

Again right from the Hodgdon web site .

Matching Shot Type and Size to Reloading Data

It is easy to assume that all shot types can be reloaded similarly; after all, they look the same – being round balls of metal. However, in loading shotgun shells, this assumption cannot be further from the truth.

The two characteristics of shot that change reloading data are shot hardness and density.

Shot hardness has a direct effect on chamber pressure. Softer shot produces lower pressure; harder shot raises chamber pressure dramatically. The softest shot type is lead. The hardest shot types are steel and tungsten. Bismuth falls between lead and steel. This is the primary reason that lead shot reloading data can never be used with any other type of shot.

Shot density affects how much room in the shell case the shot charge will take up. To try to simplify shot density, think of it this way:

A coffee cup of steel shot weighs less than a coffee cup of bismuth shot
A coffee cup of bismuth shot weighs less than a coffee cup of lead shot
A coffee cup of tungsten shot is heavier than all the others

Just remember, in shotshell reloading the reload data must be specific to the type of shot being used. Hodgdon reloading data meets this requirement.

These guys are ballistic experts .

What you are suggesting is unsafe I and hope no else follows your practice .

Believe what you want . 1 data sample will not tell what might happen in the next load .

Mark

You just agreed with me again: “ The two characteristics of shot that change reloading data are shot hardness and density.” No mention of length of payload. You might consider giving up reloading and taking up bowling.

Ron , your a funny guy. You win.

Good day.

You are a wise man