Texas10,Originally Posted by Texas10
These things tie together and will try not to blur for the sake of clairty.
1 & 2) Don't know what books you are using(how old), but this is a classic case of misunderstanding the oft understated warnings. ALL powders come with a warning, stating to "Drop loads 10% when switching lots". If you double check the only one who lists nominal variations(Western), you will see that lot variations of 10% between powders is completely reasonable. Hodgdon's current data shows you to already be over max by charge, and matching book max velocity. So here is the why: No one lists lot numbers tested, or if they themselves tested or merely re-printed the data. All good data comes from SAAMI minimum spec universal receivers and minimum spec bore and groove barrels. You are working with a mass produced animal, which will have some amount of larger tollerances. Meaning you will bleed more gas, and have lower velocities. So as was stated, whenever you match book velocities, you beat book pressures. So compared to current Hodgy data, your lot is burning faster. The next fly in the ointment is the cartridge and powder. The 243 is imfamous for having wild unexplained pressure excursions when using slow powders. It is usually more troublesome with heavier bullets, but remains in any case. So that could be playing into this as well.
As for the Mag primer comment. Remember that magnum primers came from a request of Roy Weatherby. He himself didn't like shooting his 300 case to full load pressures. After using that case in the Rockies with substantially downloaded capacity, he found ignition issues. Many will claim that it is for ball powders, which is only sort-of half correct. It is true that ball powders will have more air gap between particles, and with a substantially reduced case fill; some very old tech ball powders could actually run-out of air production to sustain ignition if the flame front wasn't aggressive enough. Speer was a leader in that "change", but that didn't happen until 1989-ish. Aluminum was one of the additives to have more "Sparklers" if you like, to aggressively ignite things. However total output isn't substantially increased. No doubt, they are different, but not massively so. All things depend of course, but in my 308 & Creedmoor, swapping magnum primers with standard produced no significant differences detected by the Pressure Trace. Not to say that ALL primers are the same, nor that all powders and loads will be the same. But don't take a sky is falling claim as gospel. Simply remember that when you switch any component, things change.
3) The throat is up to you to determine. I honestly haven't used a books OAL in so long, I can't tell you what any of my rifles are. I always load them for themselves. So take an un-primed, sized case and just barely seat a bullet. Then drop it in the chamber and slam the bolt home. Carefully extract it and measure, this tells you your jam length. Back-off as appropriate for your own desire, or mag length. Personally I like 1/32" of jump, unless a mag length issue arises. While velocity suffers when seated more deeply, I personally think that far too much is made of the importance of jump length for accuracy. There are shooters out there that perhaps it matters for, but not the masses. In my rifles even when chasing my mile targets, ALL bullets get seated to the 32nd jump. Any lack of accuracy, assuming proper powder charge work was done, isn't from bullet jump; it's me missing the wind calls.
Cheers
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