Okay guys, here's a brain teaser for y'all. Which situation creates more pressure? (Assume equal powder charges)
1. Bullet seated just off the lands (say .010")
2. Bullet seated .050" off the lands
Before y'all yell out an answer, I want ya'll to stop and ponder this for a moment. I would imagine that most people would respond by saying situation 2 since the bullet is taking up case volume. Sounds good to me.
However... situation 1 has the bullet very close to the lands, which inceases the opportunity for pressures to build faster and higher. As the bullet pushes into the lands, I would suggest that it stops moving slightly because the pressure is not enough to move it through the lands. Pressure now builds VER RAPIDLY. After this sudden increase (or spike) the burning powder can continue its normal progressive burn. But, the pressure started off higher due to the closeness of the bullet to the lands, thus a higher overall pressure. When a bullet is far from the lands, it has some distance to move first, allowing a steady build up of pressure. By the time the bullet reaches the lands, there is enough pressure now to allow for a gentler shove into the lands.
Two things can come from this. One, a slight increase in velocity can occure by seating the bullet farther out (and yes, my tests have shown this). Two, and this is the dangerous one, when reloading, if the bullet is close to the lands, PLEASE BE CAREFUL WITH MAX CHARGES!
I had some .308s loaded with 48 gr of Varget. The bolt was kind of sticky and accuracy was aweful. I did not pull the bullets... I actually pushed them into the case another .020". No sticky bolt, or pressure signs on cases, primers, etc. (accuracy was still aweful).
The point of all of this is, I've read posts where a guy is worried about pressure, so he moves the bullet farther OUT, to create more powder room. That is the wrong thing to do.
Now, what do y'all think of my brain teaser? Like I said, think through the scenareo first before y'all make a hasty reply.