Case capacity question

[Clem Bronkoski]

On my most recent post I had found an accurate load for my 300WM using 180 gr Berger Elite Hunters. This was using Barnes brass. Just out of curiosity I got some H110 pistol powder and filled a couple of the cases then weighed for an average. I then filled some of my Petersen "long" brass for an average. The Barnes cases held 90 gr and the Petersen held 93 gr. Being that the Petersen was slightly longer is it enough to worry about differences in accuracy from the established load?

 

[Seabeeken]

When changing components, it is best to back the load down and work back up with the new components. A load worked up in the Petersen cases might be hot in the smaller capacity Barnes cases

 

[Clem Bronkoski]

Well this is just the opposite SeaBee

 

[Tiny Tim]

Not certain what "slightly longer" is, but if enough to make 3 gr difference, it may be problematic. Try trimming a Peterson case to the same length as the Barnes brass and check your results (I am assuming this is what is intended by "longer case"). Also, do this with fire formed cases. Generally, Peterson cases are thicker and presumably tougher, thus they generally have a reduced case volume. Not always, but usually.

And as @Seabeeken pointed out, whenever changing components, its always best to back off and work back up.

 

[Russ-T]

Well this is just the opposite SeaBee

You stated that the Barnes held 90gr. and Petersen held 93gr.

@Seabeeken is correct. The smaller case capacity of the barnes will create higher pressure.

By "Slightly Longer" I'm assuming you mean the brass length ie: neck length.
In a 300 Win Mag. with that bullet, the neck length should not matter regarding case capacity of the loaded cartridge. The bullet will be seated below the shoulder.

Regardless, I would trim both cases to the same length and do the measurements again.

Otherwise, you have faulty data.

 

[BRADMOTO]

He's using Pete "Long Brass". They make them longer in the body so there's less stretch upon initial firing and essentially changing the head space point from belt to shoulder. Reduces case stretch up to .020" in some 300WM chambers. Pete makes it for 7RM too.

Case capacities & case composition in how strong the pockets and case heads are all over the show with predicting what is going to happen. So, the best and tried and true way to approach load development with any new brass (Any component) is to start reduced charge and work up to where signs of pressure begin to show. I load to what the brass can handle.

Pete & Alpha brass will hold pressure better than a soft Hornady or Federal case even though the Pete & Alpha have less capacity and generating more velocity/pressure. I monitor the primer pocket growth from initial firing and compare to the virgin pocket size. I stop increasing charge weight if I see .0005 growth of the pocket. Getting .001 growth upon initial firing is high pressure for that brass.

 

[VinceMule]

Are you using Deltronic pins to measure the primer pocket size?

 

[lancetkenyon]

Just a question. Why are you not using water to determine case capacity difference?

Was the Barnes brass once fired, as in already blown out and formed to your chamber? That would be a good comparison to the Peterson Long brass.

 

[med358-boise]

There is no way to consistently predict differences in accuracy when switching brands of brass and using the exact same load. I assume, you acquired the Petersen cases with intention of shooting them. So, load a few up and shoot them.

I would also add that using a spherical pistol to measure case volume is not an optimal method when trying to assess something about rifle loads, use water or while not perfect at least use the powder for the load you are going to shoot and fill the case in increments and keep tapping the case as you fill to settle the powder to give you a better relative comparison number. But again water is the right approach.

 

[Clem Bronkoski]

That is the reason I used the pistol powder because of the fine granules. No settling as would be with the extruded powder.
I figured that would be a good fill without inducing water to the cases then having to go thru a drying process.

 

[BRADMOTO]

Are you using Deltronic pins to measure the primer pocket size?

Another type of pin gauge. I got it down so much I can tell with my high grade calipers though.

 

[Clem Bronkoski]

Man it's very hard to measure a hole that smallest with a dial caliper. I'm positive from my 30+ years using M&TE you'd not get accurate repeatable results - especially to .0005". Pin gages are definitely the best way to go. Or a caliper with specialized jaws or internal mic.

 

[BRADMOTO]

Man it's very hard to measure a hole that smallest with a dial caliper. I'm positive from my 30+ years using M&TE you'd not get accurate repeatable results - especially to .0005". Pin gages are definitely the best way to go. Or a caliper with specialized jaws or internal mic.

Yeah well I am getting repeatable results and have for years. But never mind my tools, the method is solid.

It's also a relative measurement, like most things in hand loading are.

 

[Idaho Lefty]

That is the reason I used the pistol powder because of the fine granules. No settling as would be with the extruded powder.
I figured that would be a good fill without inducing water to the cases then having to go thru a drying process.

I understand Why, you used, the Pistol Powder ! ( Cleaner, NO Mess / cleanup of,.. Water ! )
Like med358-boise said,.. "load a Few rounds, go Shoot" and check the Point of Impact against, the Old load so that,... YOU, know.
Probably out to 200 yds NOT, an issue But at, Long range 400 yds, Plus,.. Probably.
Stick with, One Brand of Brass at, a time for, Best results. On Magnum Pressured Brass, 5-6 shots and the Primer Pockets are, usually, DONE !