.243 N150 87grn V-Max

[pothunter]

I was using the Lee manual which gives the maximum COAL including bullet as 2.710" so the length of the bullet is pretty irrelevant isn't it? Not being funny but surely a longer bullet just sits deeper in the the cartridge? As long as the overall length is under 2.710" its safe?

When you look at the load data from powder/bullet manufacturers or the Lyman manual, there is a different COAL for different bullets.

The seating depth has an impact on the internal ballistics of the cartridge.

If you seat a short bullet long there is more space in the case, so the ignition, pressure and velocity all change because the optimum case fill isn't being achieved, also the bullet will hit the rifling earlier, causing a change in the pressure curve.

If you seat a long bullet short you are possibly creating a compressed load.

The max COAL simply means that the round will safely fit in any SAAMI spec chamber, it doesn't automatically follow that rounds loaded to that length are safe in terms of pressure, are efficient, or accurate.

In my Lyman book an 85gn HPBT is recommended to be loaded to 2.615" and a 90gn FMJBT loaded to 2.650", these are the lengths they used when testing loads, and the pressure figures published were at that length.

[phil384]

Yep, I get it, thanks for the info