Case volume, OAL, pressure & velocity?

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BluRidgDav

New member
Theoretical question for all of you hand-loading gurus out there: How does case volume/OAL affect pressure & velocity?

Let's say that I have a .460 S&W revolver, which can also fire .454 Casull and .45 Long Colt ammunition. If I hand-loaded the exact same: primer, powder, & bullet, into each of those three cases, at the proper seating depth for each cartridge, what would be the resultant pressures & velocities ???

Similar, but not identical question:
Is it possible to achieve higher bullet velocity, by using a larger powder charge, in a larger case, while keeping pressures at the same level, in both cartridges?

Example: using the same 250 gr bullet, and enough powder to achieve the same 14,000 CUP pressure in both cartridges, but, using two different cases: .460 S&W and .45 LC. Which one will have the higher velocity ??

Thanx, Dave.
 
BluRidgDav said:
Theoretical question for all of you hand-loading gurus out there: How does case volume/OAL affect pressure & velocity?

Let's say that I have a .460 S&W revolver, which can also fire .454 Casull and .45 Long Colt ammunition. If I hand-loaded the exact same: primer, powder, & bullet, into each of those three cases, at the proper seating depth for each cartridge, what would be the resultant pressures & velocities ???

Similar, but not identical question:
Is it possible to achieve higher bullet velocity, by using a larger powder charge, in a larger case, while keeping pressures at the same level, in both cartridges? Yes.

Example: using the same 250 gr bullet, and enough powder to achieve the same 14,000 CUP pressure in both cartridges, but, using two different cases: .460 S&W and .45 LC. Which one will have the higher velocity ??

Thanx, Dave.
Click to expand...

In general for handguns with the same load:

Less case capacity, either by a shorter cartridge, thicker case walls, or seating the bullet deeper, increases pressure and velocity.
 
Case volume affects start pressure by decreasing pressure for added volume.... but... during the time between initial ignition and when the bullet hits the rifling pressure escapes around the bullet out the barrel. With my 30-06 there is a curve. So for a pistol if you are talking three different cases but the same jump to the rifling the larger case will always have more potential for velocity because less pressure alows for more powder. Different powders and bullet weights will affect the pressure curves. With my 30-06 there is a sweet spot just off the lands that will give me the highest safe velocity. The dynamics of the pressure curve depend on throat distance and powder burn rate as well as the weight and length of the bullet. Logic make one think that the longer the oal the lower the pressure but as gas escapes around the bullet before it seals the barrel pressure is lost. As long as all the guns have the same pressure limitations I think the the longest case will always be able to produce the most velocity.
 
BluRidgDav asked:
How does case volume/OAL affect pressure & velocity?
Click to expand...

In general, the more empty space in a cartridge case, the slower the pressure of the burning powder will build and it will peak at a lower level.

Where OAL comes into play is that it is like putting a cork in a bottle; the further down you push the cork, the less empty space there is in the bottle.

The important think to recognize is that as the empty space in the case decreases pressure will increase BUT THE RELATIONSHIP IS NOT LINEAR. Depending on the cartridge and the powder, small reductions in case volume can cause huge increases in pressure. Seat a bullet 30/1000 (that's 0.030) inch deeper than what the manufacturer or the powder company tested and you would be doubling the pressure.

In general, the COL given by the manufacturer or publisher of the load data should be closely followed.
 
OK, now let me change the revolver to a S&W Governor . . . . .

Given the extremely long cylinder, could handloads be assembled, using longer cases (like .460 S&W), and then loading the bullets as far out (long) as practical, to create a large internal volume, to produce increased velocities while keeping pressures low (14K-21K psi), so as not to damage that revolver?

Thanx, Dave.
 
Depending on the cartridge and the powder, small reductions in case volume can cause huge increases in pressure. Seat a bullet 30/1000 (that's 0.030) inch deeper than what the manufacturer or the powder company tested and you would be doubling the pressure.
Click to expand...

This can be true.

Depending on the cartridge and the powder, small reductions in case volume can cause no detectable increase in pressure. Seat a bullet 30/1000 (that's 0.030) inch deeper than what the manufacturer or the powder company tested and you could be making no significant change at all.
Click to expand...

This can also be true. The key is this,, Depending on the cartridge and the powder,
 what makes a considerable difference to a 9mm or .40 pistol round might make no difference at all to a .45-70 round.

OK, now let me change the revolver to a S&W Governor . . . . .

Given the extremely long cylinder, could handloads be assembled, using longer cases (like .460 S&W), and then loading the bullets as far out (long) as practical, to create a large internal volume, to produce increased velocities while keeping pressures low (14K-21K psi), so as not to damage that revolver?
Click to expand...

I'm not quite sure what you are asking. Loading the bullet as long as possible to create the greatest internal case volume practical DOES NOT produce increased velocity all on its own.
 
44,

I should have included that I would also be judiciously increasing the powder charges, to achieve the increases in velocity, while watching (or measuring) for excessive pressure levels.

Thanx for requesting clarification, Dave.
 
BluRidgDav, I don't think you're going to see any excess pressure signs at 21K psi. That's a very low pressure.

With respect to your question, the longer you load with your longer brass, the lower the pressure. You should be able to add more powder so that by the time you equal the pressure of the shorter brass and OAL, the velocity would be higher than you would get with the shorter brass/OAL.

See the link below for an example of how using shorter bullets can achieve this (same principle). Scroll down to the first Table and its explanation.

http://www.shootingtimes.com/reloading/handloading-960-rowland/
 
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