04-15-2020, 06:16 AM
I found this in the remarks section of more bullet jump research from Precision rifle blog. If the quote below is true then my understanding that seating the bullet out farther (but not touching the lands) would result in less pressure is wrong, in fact opposite of what I thought!
"Maybe the only thing that seems like it might be fairly agreed upon is seating the bullet in the case so that it contacts the rifling in the throat increases the peak chamber pressure, which is not desirable. (From Dr. Vaughn in Rifle Accuracy Facts). Dr. Vaughn also said, The pressure change caused by changing bullet seating depth in the case can also be deduced from Reference I for 0.308 caliber bullets. The peak chamber pressure will drop about 1000 psi for every 30 mils of additional distance (free run) between the bullet and contact with the lands in the throat. In other words, if you seat the bullet so that it has about 60 mils of free run before contacting the Lands, the peak chamber pressure will be reduced by about 2000 psi. So its not just that when you are seated into the lands that peak chamber pressure is increased, but the further you get from the lands the more you reduce peak chamber pressure. But, Dr. Vaughns next sentence there is, This means that the chamber pressure is not very sensitive to seating depth. So, I guess in the grand scheme of things a 2000 psi reduction in peak pressure isnt much."
"Maybe the only thing that seems like it might be fairly agreed upon is seating the bullet in the case so that it contacts the rifling in the throat increases the peak chamber pressure, which is not desirable. (From Dr. Vaughn in Rifle Accuracy Facts). Dr. Vaughn also said, The pressure change caused by changing bullet seating depth in the case can also be deduced from Reference I for 0.308 caliber bullets. The peak chamber pressure will drop about 1000 psi for every 30 mils of additional distance (free run) between the bullet and contact with the lands in the throat. In other words, if you seat the bullet so that it has about 60 mils of free run before contacting the Lands, the peak chamber pressure will be reduced by about 2000 psi. So its not just that when you are seated into the lands that peak chamber pressure is increased, but the further you get from the lands the more you reduce peak chamber pressure. But, Dr. Vaughns next sentence there is, This means that the chamber pressure is not very sensitive to seating depth. So, I guess in the grand scheme of things a 2000 psi reduction in peak pressure isnt much."