Seating depth, powder charge and speeds

[bstomper]

I am hoping someone can clear this up for me.
without getting to technical, is it the amount of pressure the powder charge gives in a certain case volume, that causes the bullet speed. Basically, seating the bullet longer will give more room for powder in the case. Will this added powder give the bullet more speed. Or is the added powder simply just filling the case to give the same pressures and speeds I had before
For ease of explanation I will use random numbers. If I have a load at a COAL of 3.300"and a powder charge of 55 grains with a given pressure and a speed of 2900 fps, if I seat the bullet longer to a COAL of 3.400" and still 55gns, obviously the case capacity is bigger now so I am assuming the pressure should be lower. If I bump up the power charge to give me the same pressures I had before, will the speed still be the same at 2900 fps or will it be faster.
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. Hope this makes sense. lol

 

[Phil Rizzo]

Moving the bullet closer to the lands can /does increase pressure, in addition to more powder.
All relative.

 

[Shane Lindsey]

Adding more powder will increase the velocity for same seating depth. If you reduce seating depth a good bit, you may also increase velocity. Seating too long, may also increase velocity if too close/ in the lands.

What loading long typically allows you to do, is load more of the slower burning powder that would tyically cause you to have compressed loads.

When doing seating tests, I have not seen velocity changes with the fine tuning depths. I have seen it increase with significant seating depth changes (deeper).

Make sense??? Not really...It's all voodoo man

 

[Tiny Tim]

Generally speaking, from SAAMI spec, loading longer increases case volume and decreases pressure, which allows more powder which increases velocity (as previously stated, usually using slow burning powders).
At either extreme, either seating deeper or longer, will increase pressure either by decreasing case volume or by bullet getting too close to the lands.

For example, with the same powder charge in my 300 RUM, starting .015 off and increasing seating depth in .015 increments, I would see an approximate 10 fps decrease each step as I got further from the lands til about .045 off.

 

[K.E.C. Darkside]

What They Said.