The shooting discipline where such minutia matters and has a definite impact on group size and score is LR BR. We look for wide tuning nodes with both powder charge and seating depth. They are rarely as wide as we'd like them to be.
A common concern is having a load go out of tune in the middle of a shot string. What puts the load out of tune is throat eroding and increasing the jump or decreasing the jam. This is why we keep trying to find smaller cartridges that use less powder. Less powder should cause less throat erosion which means there is less chance of the load going out of tune during a record string.
Most of the time chasing the lands keeps the load in tune. Then again, most of the time we tune the right before the match and tweak the charge and/or seating depth. Sometimes I'll wind up with the same load for several matches. Sometimes I'll need a slight tweak in powder or seating. I think powder makes a bigger change in the tune than seating when fine tuning.
There are obviously two big factors affecting the tune as the throat erodes. The first is the change in throat changes how the bullet engages the rifling, which can indeed change how the load shoots. The second, when chasing the lands, is the increased case capacity will eventually change how the powder charge is shooting as well. If we are chasing the lands .001 to .002" at a time, it will take a while before the case capacity issue will show up. Especially when a 6 BRA only erodes the throat .010 to .015" in 1000 rounds. Then again, it's not a linear erosion, it stays put for a while then makes a jump.
I have also seen that when I can get a load to tune with the bullets .015 - .018" off the lands, it's takes a lot more erosion to affect the tune vs having the bullet very close to the lands.
I measure the throat after every match and load development session.
A common concern is having a load go out of tune in the middle of a shot string. What puts the load out of tune is throat eroding and increasing the jump or decreasing the jam. This is why we keep trying to find smaller cartridges that use less powder. Less powder should cause less throat erosion which means there is less chance of the load going out of tune during a record string.
Most of the time chasing the lands keeps the load in tune. Then again, most of the time we tune the right before the match and tweak the charge and/or seating depth. Sometimes I'll wind up with the same load for several matches. Sometimes I'll need a slight tweak in powder or seating. I think powder makes a bigger change in the tune than seating when fine tuning.
There are obviously two big factors affecting the tune as the throat erodes. The first is the change in throat changes how the bullet engages the rifling, which can indeed change how the load shoots. The second, when chasing the lands, is the increased case capacity will eventually change how the powder charge is shooting as well. If we are chasing the lands .001 to .002" at a time, it will take a while before the case capacity issue will show up. Especially when a 6 BRA only erodes the throat .010 to .015" in 1000 rounds. Then again, it's not a linear erosion, it stays put for a while then makes a jump.
I have also seen that when I can get a load to tune with the bullets .015 - .018" off the lands, it's takes a lot more erosion to affect the tune vs having the bullet very close to the lands.
I measure the throat after every match and load development session.
