Gentlemen:

Can one or more of you who may know the answer(s)give me a quick run down on the relationship between pressure and bullet design? I have read and heard that bullet design such as in the TSX, Northfork, and others, can/do reduce pressure. I am told they do this by creating less drag on the rifling by having less bearing surface. Makes sense to me.

However, I always thought of pressure in terms of "chamber pressure." I always believed that the point in the firearm where pressure reached its peak was in the chamber. Is this true? If it is true, then how does a bullet that has already left the chamber infulence pressure? Hasn't the pressure already reached its peak? And doesn't the pressure immediately begin to disapate as the bullet travels down the bore and the gases bleed through the grooves?

Seems to me, an admitted layman, that peak pressure is realized at the momment the bullet is forced from the case and that pressure lessens as the bullet travels down the bore. So how does bullet design influence pressure?

BTW. I am more than willing to admit that any and all assumptions I've made are wrong. I'm just looking for an informed answer.

For the purpose of your answer, please talk in the context of a medium bore center fire bolt action rifle.

Many thanks. Tom

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quote:

Can one or more of you who may know the answer(s)give me a quick run down on the relationship between pressure and bullet design?

Should we not be mentioning, in addition to the above list, also the innovative GSC design? I think Gerard deserves credit for designing a bullet with far less engraving resistance than other bullets.

Warrior

The TSX and North Fork will load with less pressure than an X bullet, but sure build more pressure than a conventional cup-type bullet like a Sierra or even a Nosler. For me the TSX takes a grain less to reach the same velocity as a NP, the North Forks, sometimes 2-3 grains less, in my 9.3x62 uses the identical load to the same velocity as a NP. You just have to be careful.

Pressure usually will "peak" just in front of the chamber. How far depends on the powders burn rate as much as the bullet used. The "peak" is called "chamber pressure" because that is the point we place the gage or other measuring device we use to measure it not down the barrel.
The force needed to engrave the bullet and get it moving down the barrel can alter the point in the bore the pressures peak. A bullet that starts easily may be a few milimeters farther down the tube, giving more volume/area for the expanding gas to fill and effectivly MAY reduce the maximum pressure developed. It will delay the point pressures peak some. The velocity will also be reduced and this is why people report adding a gr or 2 at times to their loads when useing these bullets & powders to get velocity back up. Once the velocity is back to expected peak pressures should be at a corosponding level but without test equipment we don`t really know. If you get 2900fps with 150gr bullet "A" and powder "X" then to get the same velocity with bullet "C" and the same powder the same relative pressures are needed.

quote:

Originally posted by ALF:
Projectile factors that affect pressure:

1. Sectional density.
2. Total Bearing surface.
3. Radial deformation ( upset)
4. Jacket and core material properties.

and, of course, 2 and 3 above are greatly influenced by the barrel characterics

Many thanks to you all. I got it!
Regards Tom