The Sierra Maunal lists 39.5 gr with a 120 gr SMK seated to a COAL of 2.785 inches as a copressed load.
However if I seat to a COAL of 2.91 inches, it is no longer a compressed load. Will pressure go up or down?
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June 28, 2008, 02:16 PM
Any time you increase the OAL on a given charge with the same bullet, your pressure will be lower. If you are using a different (longer) bullet, be careful, as you might seat too deep and spike the pressure.
June 28, 2008, 02:18 PM
It will go down slightly, because of the increased case capacity with the long seated bullets.
Compressing a charge has no effect on pressure one way or the other as long as it is a safe load to begin with.
June 28, 2008, 02:48 PM
Ok then a follow on...
the 120 GR SMK is 1.179 inches long.. seated at 2.910 COAL means there is only .297 inches actually in the neck/case... which is > caliber .260
What effect would the BT design have on this? Or should I just stop worring and obessing and go shoot the damn rifle already?
June 28, 2008, 02:58 PM
The only sure way to find out what you need to know, as far as load development, powder charge, seating depth, etc, is:
Go shoot the Damn Rifle Already!
You can stew & worry over all the minor details, and none of it does a bit of good until you start testing loads at the range!
June 28, 2008, 03:57 PM
While this is not your cartridge it is still interesting , showing how pressure reacts to seating depth, see page 48. I believe this was used by Harold Vaughn. This link takes a minute to open -