Interpolating Load Data

[powerspc]

Been at this a while and still learning every day.

I do not believe that load data is linear, but I am wondering if the data points are close enough if a linear interpolation will provide a decent estimate, e.g.,;

For a particular powder and bullet I see this load data:

208 gr. bullet / 74.5gr starting load
220 gr. bullet / 72gr starting load

I am loading 215gr bullets, would 73gr be a reasonable place to start?

 

[Deleted member 113831]

Been at this a while and still learning every day.

I do not believe that load data is linear, but I am wondering if the data points are close enough if a linear interpolation will provide a decent estimate, e.g.,;

For a particular powder and bullet I see this load data:

208 gr. bullet / 74.5gr starting load
220 gr. bullet / 72gr starting load

I am loading 215gr bullets, would 73gr be a reasonable place to start?

Typically, when unsure or data is unavailable, you pick a similarly constructed bullet in the next higher weight class and use that data as-is to start the work up.

 

[spamassassin]

I'd go by bearing surface length, not mass. That's what matters for friction. The mass difference shouldn't matter much in the buildup of pressure.

 

[Deleted member 113831]

I'd go by bearing surface length, not mass. That's what matters for friction. The mass difference shouldn't matter much in the buildup of pressure.

What is your data for that statement.

 

[memtb]

What is your data for that statement.

The original Barnes X bullet (without the grooves) often exhibited much higher pressures than a typical cup and core of similar weight.......bearing surface! The bullet being significantly longer, due to copper weighing significantly less than lead. With same bore diameters, and same weights = longer bearing surface= greater resistance to movement = higher pressures! JMO. memtb

 

[Deleted member 113831]

The original Barnes X bullet (without the grooves) often exhibited much higher pressures than a typical cup and core of similar weight.......bearing surface! The bullet being significantly longer, due to copper weighing significantly less than lead. With same bore diameters, and same weights = longer bearing surface= greater resistance to movement = higher pressures! JMO. memtb

So you don't think the difference in hardness/plasticity between copper cup/lead core construction vs. the solid copper has anything to do with it? The relief bands cut into the TSX line reduce pressure by giving the copper some place to go when the bullet engraves, because the solids don't compress.

You can take a lead core match bullet or hunting bullet and smash it flat with a pair of pliers in your hand. Try that with a solid and tell me how that goes.

 

[2aBaC̶a̶]

Been at this a while and still learning every day.

I do not believe that load data is linear, but I am wondering if the data points are close enough if a linear interpolation will provide a decent estimate, e.g.,;

For a particular powder and bullet I see this load data:

208 gr. bullet / 74.5gr starting load
220 gr. bullet / 72gr starting load

I am loading 215gr bullets, would 73gr be a reasonable place to start?

Short answer is yes.

 

[FuhQ]

It's not linear, but I have noticed some extremely repetitive results in certain loads for certain cartridges.

Example: One load that we experimented with was for the .308 Winchester. After testing MANY different rifles, brass, primers, and bullet types, but ALL the same weight, we found that 44.0 grains of Varget with a 168gr bullet was a consistently accurate load. It may not have been THE MOST accurate load for that rifle, but it was still an accurate load in nearly all rifles it was tested in.

There were several others, but this was MANY years ago, and I can't remember off the top of my head. A lot of life has happened since then...

 

[memtb]

So you don't think the difference in hardness/plasticity between copper cup/lead core construction vs. the solid copper has anything to do with it? The relief bands cut into the TSX line reduce pressure by giving the copper some place to go when the bullet engraves, because the solids don't compress.

You can take a lead core match bullet or hunting bullet and smash it flat with a pair of pliers in your hand. Try that with a solid and tell me how that goes.

I’m not going to suggest that the difference in metallurgy will not influence a difference in pressures! However, by cutting grooves into the bullet, will definitely reduce the surface bearing area, which will reduce the pressures! memtb

 

[spamassassin]

What is your data for that statement.

Simple physics... the kind they teach in high school should answer that for you.

 

[spife7980]

I think skookums point is that there are a lot more variables that should be considered if making broad statements like that.

 

[Deleted member 113831]

I think skookums point is that there are a lot more variables that should be considered if making broad statements like that.

Yep.

With bullets of similar construction, the additional mass of the next weight class of bullet has much more influence on the load than a few more thousandths of bearing surface.

If it were not the case, then loading manuals like the Speer, Nosler and Sierra wouldn't be able to list a variety of bullets in the same weight class under the exact same load data.