Extrapolating Data

[Dmay]

I am looking for data on a particular bullet. Manufacturer doesn't have enough testing to release data.

I want data for a 550gr bullet.
They have data for their 525gr bullet.
I intend to take their load, which they call max, knock it down 5% for the "max" part, and knock it down another 15% for the 25 grains.
Do those figures sound reasonable?

 

[Cameron SS]

I am looking for data on a particular bullet. Manufacturer doesn't have enough testing to release data.

I want data for a 550gr bullet.
They have data for their 525gr bullet.
I intend to take their load, which they call max, knock it down 5% for the "max" part, and knock it down another 15% for the 25 grains.
Do those figures sound reasonable?

You have not provided enough info. Are we talking same cartridge/ diameter?

What are the bearing surfaces of each bullet?

A lighter bullet with a longer bearing surface may have greater friction and initial resistance than a heavier bullet, and may require the same or more powder at a slower burn rate in order to achieve an optimal result.

Alternatively if the bearing surface is significantly less than the heavier you may need a faster burning powder.

The difference between 550 and 525 is only 5% of your mass. In the grand scheme of things thats not a lot.

Take a look at load data for a 308 and compare a 200 gr load data with 210 gr load data of the same powder.

Do the same between a 6mm in 100 vs 105. I suspect youll find that if the bullets are roughly equal size than the powder charges arent that different.

 

[Dmay]

Thank you for that.

Yes, it is same cartridge. Bearing surface should be basically identical because it is a machined bullet with a driving band.

 

[Cameron SS]

Thank you for that.

Yes, it is same cartridge. Bearing surface should be basically identical because it is a machined bullet with a driving band.

So you are going to to the heavier bullet using data from the lighter bullet correct?

If you have data for the 525 gr, look at the different powders they used, and start with the slower burning powders on the list, and you'd probably be fine to just start with the min load and go from there.

Whats the powder starting charge weight for the 525gr ? I'd back off 1-2% if you were still concerned about an extra margin of safety.

 

[Dmay]

Yes correct. I got data for the lighter bullet.
I only got one load from them, and they are calling it max.
Powder is V20N29, which is what I had planned to use anyway. 188gr in their example.
It's a 416 Barrett by the way, not sure why I was keeping that a secret.

Anyway, thank you. Just comforting to hear some feedback when a guy is sorta stepping into the unknown.
Soon as I load one up and see a velocity, I can move forward with confidence. And then to stretch it out with an unknown BC may burn a little powder, but we'll get 'er figured.

 

[B]

I have done some pretty accurate extrapolation using bullets of similar design. For example I had 200 grain Barnes XPB. I had load data for 220s but not 200. I extrapolated using a similar method as described and arrived almost exactly where I figured I should with velocity. With great care it can be done but it's not something I'd ever recommend to someone without a solid knowledge of reloading.

 

[Ganderite]

Each rifle needs a load developed for it. Start low and work up. Their Max does not matter. You have to find the Max in your rifle.

The start laod you suggest seems reasonable, but you might have to load down from there, depending on what you find.