Case capacity load adjustment

[mdmp5]

I am shooting 300 WM in the following load:
210 SMK
77.3g H1000
Wolf LRM primers
Lapua brass
0.005" off lands
This load is very accurate for me, gives me about 2835 fps, and no signs of pressure.
I loaded the same bullet and charge in some Nosler brass I had, and the bolt was really sticky to unlock. So when I got home, I measured the difference between 2 pieces of randomly picked Nosler and Lapua brass. Here was what I found:

Lapua
Case capacity: 94.4g H20
Weight: 216.6g

Nosler
Case capacity: 91.8g H20
Weight: 238.1g

How much should I reduce the load in the Nosler brass. Note that I didn't chrony the load out of the Nosler brass, but if I had to guess, I'd say it was a bit faster than the Lapua loads.

I don't have much time for load development, otherwise I wouldn't be asking. Thanks.

 

[Tripwire]

Re: Case capacity load adjustment

No magic wand or voodoo potion for this friend....rework the load if switching to the Nosler brass.

Checking case capacity when switching lots and brands BEFORE loading anything; never assume things will be okay; rework the load when changing components.....Basic Reloading 101.

 

[hdbiker1]

Re: Case capacity load adjustment

To me it appears you have all the numbers in front of you. Make sure to use more than one sample size of each brass to determine average capacity. Use your math skills to extrapolate the corrected charge weight.

 

[Tripwire]

Re: Case capacity load adjustment

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hdbiker1</div><div class="ubbcode-body">To me it appears you have all the numbers in front of you. Make sure to use more than one sample size of each brass to determine average capacity. Use your math skills to extrapolate the corrected charge weight. </div></div>

That'll get him a fairly good place to start reworking but it's no absolute guarantee that it'll match perfectly with the load he already has.

Gotta prove things out to be right and there's no magic formula of numbers that'll get him there with absolute certainty.

Rework the load.......

 

[hntbambi]

Re: Case capacity load adjustment

Take an average of 10 cases and compare the two. With the one data point you provided, the Nosler brass holds 2.75% less capacity. Reduce your load by 2.75% and see how it compares. This should narrow your load re-work significantly.

 

[Greg Langelius *]

Re: Case capacity load adjustment

It is one of the most basic rules of handloading that when a load component substitution takes place, the load changes, and should be reworked.

The case volume difference you relate amounts to something more than 2%. If I varied my charge by 2% (in your case by about 1 1/2gr), I'd be out in the hinterlands regarding my load's performancce.

I think the logic is inescapable. You need to step down at least 3-4% (2 1/2 to 3gr) of charge weight and redevelop the correct charge weight for that brass and bullet combination.

If you reload in order to attain optimal performnce, then the logic follows that you really do need to take the time to find a good approximation of an optimal load.

Greg

 

[mdmp5]

Re: Case capacity load adjustment

Thanks guys. The advice you gave is very logical. I will just have to step it down and rework it. Sucks having 2-3 different types of brass, but that is the problem with 300 win mag, when you only have 100 pieces of lapua brass.

 

[WDL]

Re: Case capacity load adjustment

I agree a re-work of the load is necessary. I also agree at least 6 pieces of brass need to be averaged.
QuickLoad can predict the new load by first calibrating the original load to velocity/case capacity, then substituting the new case capacity and adjusting the load to the original velocity. But a re-work of the load is still necessary.

 

[flashhole]

Re: Case capacity load adjustment

I would start by reducing it by the H2O ratio of the two cases. In your case the math works out to 75.2 grains of powder.

 

[Greg Langelius *]

Re: Case capacity load adjustment

That's pretty close the the number I was thinking, too.