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Old March 4, 2012, 09:15 PM   #1
Kayser
Senior Member
 
Join Date: May 29, 2002
Location: Illinois :(
Posts: 550
Bullet length as it affects COL.

This is something that you pretty much never see discussed, but which has always seemed extremely relevant to me. In short:

- A given recipe might specify a specific bullet (eg, 240 gr hornady XTP), powder charge and OAL.
- Pressure is dictated by charge weight, bullet weight and OAL of the round (seating a bullet deeper shortens OAL, decreases internal case volume and increases pressure).
- Not all bullets of the same weight are the same length.

Therefore, it seems to me you must adjust OAL by the difference in bullet length from your reference bullet.

For example, my Hornady manual lists a COL of 1.600" for their 240 gr XTP 44 magnum bullet. Ok, great. But let's say I have a bag of Magtech 240 gr bullets. If you measure them, the XTP's have an average length of 0.712". But the Magtech's have an average length of 0.685"

It seems to me that this implies if you are using the Magtechs with the same powder charge, you must shorten oal by (0.712" - 0.685" = 0.027") to keep the internal volume and therefore pressure, the same.

This seems quite obvious and relevant, but you pretty much never see this discussed in reloading circles. The manuals don't list bullet length (at least the ones I've seen).

Anyone else find this weird?
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