Case volume differences in different brands

[jetinteriorguy]

I measured the difference in case volume using the water method between my Starline and Nosler cases for 6.5 Creedmoor. These cases were all full length sized with a body die and neck sized with a Lee Collet die and trimmed to the same length. The difference averaged .3-.4 grains. Is this difference insignificant enough to just run both with the same load? Or should I work up the load by downloading a few tenths of a grain and working back up again?

 

[Reloadron]

How much it matters will likely be a function of the VMD (Volume Metered Density) of the powder you load with. That said likely it will not really matter at all.

Ron

 

[Don Fischer]

You should read up on reloading. You change component's and you start over. Start low and work up to max. Now I have thing's I do that I shouldn't but have been doing them a long time. I don't need to ask anyone what they think of it. Like I said, been doing it a long time and never a problem.

 

[rsnell]

What balance(scale) did you use to determine the weight of the cases with and without water? If you used a balance(scale) the manufacturer claims the accuracy to be plus or minus 0.1 of a grain, the difference is 0.

 

[Bart B.]

I measured the difference in case volume using the water method between my Starline and Nosler cases for 6.5 Creedmoor. These cases were all full length sized with a body die and neck sized with a Lee Collet die and trimmed to the same length. The difference averaged .003-.004 grains. Is this difference insignificant enough to just run both with the same load? Or should I work up the load by downloading a few tenths of a grain and working back up again?

There's more spread in powder and primer fire per unit that'll mask that spread in water weight.

Besides, if the case outside dimensions were not all exactly the same, that alone will cause more spread.

I sort cases by weight to a 1% spread per lot.

 

[higgite]

I measured the difference in case volume using the water method between my Starline and Nosler cases for 6.5 Creedmoor. These cases were all full length sized with a body die and neck sized with a Lee Collet die and trimmed to the same length. The difference averaged .003-.004 grains.
What scale are you using to measure to a thousandth of a grain?

Is this difference insignificant enough to just run both with the same load?
If you really mean .003-.004 grains difference, that is essentially no difference. But, I'm skeptical of your measurement, no offense intended.

Or should I work up the load by downloading a few tenths of a grain and working back up again?
Yes, like Don said above, you should always work up a new load when changing components, but especially in this case because .003-.004 grain difference just isn't realistic.

....

 

[totaldla]

I measured the difference in case volume using the water method between my Starline and Nosler cases for 6.5 Creedmoor. These cases were all full length sized with a body die and neck sized with a Lee Collet die and trimmed to the same length. The difference averaged .003-.004 grains. Is this difference insignificant enough to just run both with the same load? Or should I work up the load by downloading a few tenths of a grain and working back up again?

I'm assuming you meant 3 - 4 grains, which would seem about right for vendor to vendor difference.

 

[jetinteriorguy]

I measured the weight on a Hornady digital scale. My bad on posting the weight difference. The difference is actually .3-.4 grains, brain fart, too early and hadn't had my coffee yet. The Nosler has the higher capacity. I'm thinking I'll drop down .9gr and work it back up and check the MV in the process to see how it compares to my present load. I'm going to edit my original post to avoid any misunderstanding.

 

[cw308]

I once thought all the cases had to be the same . I first started reloading with Win & Rem 308 cases , was loading on the low side of the listed measurements . A friend gave me his Federal once fired brass , he doesn't reload . All my cases are Full Length sized , my Win & Rem . cases would fill to the base of the neck or the top of the shoulder with IMR 4064 , when I used the Federal cases the powder almost went to the top of the case mouth , puzzeled me for a moment , checked the charge weight and dumped it into the Rem. case filled to the base of the case mouth . I lowered the charge by one grain on the thicker brass , they shot just as good . Different brands have different thicknesses and volume. Something to look out for .

 

[RC20]

I read it as 3/10 to 4/10.

Its not just the powder, its the shell as well and how it reacts during the boom.

No pat answer. Your load for the first case (if you have a good one) is a fine starting point.

If it shoots as good as you want, cool.

If not then you range up or down (keeping in mind where you are in regards to max load)

No you don't have to go all the way down and start over. If you are at the max powder any manual shows that is a different story where caution is definitely advised on the add more side.

I have measured cases by use of 748 ball powder. Granted its not to some people specs, but its a good indicator.

As I recall the relevant change in power by weight was 1/20 of the grains of the case by weight. That is in a 30-06 size case.

 

[jetinteriorguy]

Thanks, I'm definitely not near max load. This was mostly just something I was thinking about so asked the question. Not going to mess with it now but sometime in the future. I was mostly curious if the only limiting factor was case volume or if other things factor in as well and at what point do these things require another workup. Too much time on my hands, I've always done a workup when changing any component over the last 30+ years of reloading and mostly thinking maybe it's not always necessary.

 

[Unclenick]

Also important to point out is that in cartridges running with enough pressure to stick the case to the chamber and stretch, it is volume the case expands to in the chamber that affects pressure with a particular powder charge and not the resized volume. So, fire them and measure again. But in general, for small differences like that, figure the change in charge weight needed to keep the pressure matching will be about half the difference in water weight. A 0.2-grain charge difference is as small as powder measure variation. If you have a load centered on a sweet spot it can tolerate some charge variation without producing a significant POI change, so if the difference for the as-fired volumes is about the same, tune the load and you won't see a difference.

 

[jetinteriorguy]

Ah, makes sense to me. Thanks Uncle Nick. Ya learn something new every day if you're paying attention.