Just started reloading for my savage .270 and I have a question about how pressure changes with bullet seating depth and overall length/bullet jump. I've read that seating the bullet deeper will increase pressure; this makes sense since less volume with the same amount of gas will be at a higher pressure. But I've also read that reducing bullet jump by seating the bullet on or just off the lands (opposite of the first scenario) will increase pressure because the bullet has minimal momentum to overcome the friction of the lands, so it pauses momentarily which allows pressure to build higher.
Are these both true? Do the two effects tend to cancel each other out, or is one dominant? Or would the pressure graphed against coal be shaped like a 'u'?
The lands on my rifle are at 3.41", cartridge spec max is 3.34", and the Barnes recommendation for the TTSX (130gr) is 3.31" with 56.0-59.5 gr rl-19. However they also recommend seating the bullet .05" off the lands, which doesn't correspond with cartridge specific data, I guess because each rifle is different. Anyway, I tested out my first loads yesterday, seated at 3.36" and working up from 56 in .5 gr increments. Saw pressure signs at 59 so I stopped there, but a nice group at 58, so I'll try to fine tune around that.
Are these both true? Do the two effects tend to cancel each other out, or is one dominant? Or would the pressure graphed against coal be shaped like a 'u'?
The lands on my rifle are at 3.41", cartridge spec max is 3.34", and the Barnes recommendation for the TTSX (130gr) is 3.31" with 56.0-59.5 gr rl-19. However they also recommend seating the bullet .05" off the lands, which doesn't correspond with cartridge specific data, I guess because each rifle is different. Anyway, I tested out my first loads yesterday, seated at 3.36" and working up from 56 in .5 gr increments. Saw pressure signs at 59 so I stopped there, but a nice group at 58, so I'll try to fine tune around that.
