There are few universal truths in reloading and bullet set back MAY cause an increase in pressure, even a significant amount but it depends upon several factors like the powder being used, the load density, the case size, the bullet and crimp.
Some argue that reduction in volume due to setback must increase pressures, however ammunition pressure is a dynamic of many factors such as powder burn rate. The volume is not a simple constant since the bullet is moving out of the case and into the barrel while the powder is still generating combustion gas, thus the volume the gas expands into to create pressure is increasing over time.
Many powders function perfectly well as a compressed load and the amount of compression doesn't seem to make any significant differece in pressure or velocity.
I've personally shot many pistol rounds that had the bullet set back from being chambered many times and have never observed any high pressure signs in the fired cases. For commercial ammo the main issue of bullet set back is that it can reduce the feed reliability of the ammo, additional pressure is not a real problem that presents itself.
Some argue that reduction in volume due to setback must increase pressures, however ammunition pressure is a dynamic of many factors such as powder burn rate. The volume is not a simple constant since the bullet is moving out of the case and into the barrel while the powder is still generating combustion gas, thus the volume the gas expands into to create pressure is increasing over time.
Many powders function perfectly well as a compressed load and the amount of compression doesn't seem to make any significant differece in pressure or velocity.
I've personally shot many pistol rounds that had the bullet set back from being chambered many times and have never observed any high pressure signs in the fired cases. For commercial ammo the main issue of bullet set back is that it can reduce the feed reliability of the ammo, additional pressure is not a real problem that presents itself.