Using QuickLOAD, calculate MINIMUM safe load when there is no powder manufacturer's data

[THE Flapjack]

Using QuickLOAD, I need to come up with a MINIMUM safe load for the 33XC using Vihtavuori N570.
This will be used to load some break-in rounds using David Tubb's 250gr 338 Final Finish bullets.
My first thoughts are that it would be % case capacity related.

 

[Dogtown]

The minimum case fill percentage most folks use is 70% - anything less than that can be problematic. That being said, when I've been in this situation, I've just played with the % until the results are well in the grey safe zone (ie no yellow, purple, or red).

So the 33XC with N570, I'm seeing yellow at 90% fill (102.3gr) and grey starts around 87.5% (99.5gr). So if you want to shoot final finish bullets with a safe starting load as recommended, I'd load them with 96gr of N570 and be done with it. Of course, it really sucks to burn a bunch of high quality scarce N570 for break-in loads

 

[Supersubes]

Why shoot final finish bullets? Is this not a custom gun with a premium barrel?

 

[Dogtown]

According to the directions, for factory barrels you shoot all 5 levels of grit, but custom hand lapped barrels only need the last 2-3 levels of grit.

 

[TheOfficeT-Rex]

According to the directions, for factory barrels you shoot all 5 levels of grit, but custom hand lapped barrels only need the last 2-3 levels of grit.

I think the implication was "why do you think you need them at all?"

 

[Supersubes]

I think the implication was "why do you think you need them at all?"

Yes, this.

 

[THE Flapjack]

The minimum case fill percentage most folks use is 70% - anything less than that can be problematic. That being said, when I've been in this situation, I've just played with the % until the results are well in the grey safe zone (ie no yellow, purple, or red).

So the 33XC with N570, I'm seeing yellow at 90% fill (102.3gr) and grey starts around 87.5% (99.5gr). So if you want to shoot final finish bullets with a safe starting load as recommended, I'd load them with 96gr of N570 and be done with it. Of course, it really sucks to burn a bunch of high quality scarce N570 for break-in loads

Really appreciate this insight and I see nothing amiss with your suggestion.
N570 easier to obtain here and I've 6Kgs ;-)

 

[THE Flapjack]

Why shoot final finish bullets? Is this not a custom gun with a premium barrel?

Others have answered for me ;-)
To expand, having spoken to David Tubb, will only use the last 2 grits after first borescoping the new barrel.
Expensive because you have to buy the full set :-(
An upside, I'll have a hand full of fireformed cases

 

[1moaoff]

But why?

 

[THE Flapjack]

But why?

When I get the barrel in about 4 months time, I'll take a borescope photo and post it.