Seating depth, powder charge and speeds

With every additional post, all of which have a degree of fact, we are proving that this is not a simple equation, and needs to be tested in every individual rifle/powder/primer/neck tension/seating depth/bullet shape/bullet construction scenario.....im worn out just thinking about it!

bstomper said:

My rifle can only handle X amount of pressure so In my mind it is the pressure inside a given space that gives speed and not the amount of powder, the powder only fills the case to give the pressure.

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Seems like you're considering this from a load density perspective.
Lower load density causing lower velocity
higher load density causing higher velocity
You're wondering if you adjust to keep the same load density, for seating or capacity changes, will velocity hold.

Given same powder, I believe powder amount dominates.
Load density, and starting pressure from close land relationships do affect pressure. All kinds of things do.
Just not as much as powder amount.

To make sure I understand this issue, If I have more freebore added to my 28 NOS and loaded the same amount of powder, it would be a little slower. But since case volume is increased, I can increase the load and probably end up with a higher velocity (with no change in seating depth from lands).
Both the new load and the old load might could show the same peak pressure.

Is the above what would be expected?

MOA or bust said:

To make sure I understand this issue, If I have more freebore added to my 28 NOS and loaded the same amount of powder, it would be a little slower. But since case volume is increased, I can increase the load and probably end up with a higher velocity (with no change in seating depth from lands).
Both the new load and the old load might could show the same peak pressure.

Is the above what would be expected?

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Freebore doesn't affect case capacity, but it does lower pressure because of bleed off. The generally silly circular idea of larger case, more powder, hoping like crazy it will magical mean more velocity at the same pressure. Was the entire premise behind Ackley's prayers, which we untrue even way back then.
T.A.R. sent his claims off for actual pressure testing @ HP White Labs, and printed the results in Dec 1959. Ackley went on to publish most of his books and continue his false claims after definitively knowing his claims were false. For anyone struggling to keep score, that's called being a charlatan...

Kingsgr8 said:

I also think a part of the missing equation is the weight of the projectile and the fit in the barrel. It take more energy to start a 220 grain bullet than a 55 grain bullet. Thus your peak pressure changes. With a tight fitting slug in the barrel Or a heavier projectile you will also have a sustained "peak", and lower speeds.

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This may seem logical, but it assumes constants that don't exist. A 220gr bullet isn't somehow going to be "tighter fitting" unless you bought a different diameter. If you're going for the bearing surface argument, it's also not true in the sense you wish it were. 220gr bullets need a different burning speed than 55gr bullets; so that's a herring in the argument.

If you add .15 more freebore to a chamber and keep the same jump (say 20/1000) do you not have significantly more capacity for powder? I think this 28 NOS is starving for more freebore with this 170g HHT.

BTW, Ackley modified cartridges ARE faster. (Ex. .280 vs .280AI)

MOA, I wouldn't allow bullet bearing through the neck-shoulder junction.
It's no problem for a gunsmith to make adequate room, and I would also run single shot(if needed) before seating so deep.

Mikecr said:

MOA, I wouldn't allow bullet bearing through the neck-shoulder junction.
It's no problem for a gunsmith to make adequate room, and I would also run single shot(if needed) before seating so deep.

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I agree, but it's shooting .5 MOA!
But since I just completed a successful elk hunt, I may go ahead with adding freebore. Got room in the mag for longer load.