Re: Target Shooting Loads
Seating on the lands is common in benchrest circles.
They're looking for groups measured in ten thousands of an inch and are trying to eliminate any variation in that miniscule amount of bullet jump and any possible yaw error before it engages the rifling. If the bullet has to jump to the rifling, there is always a variable on how it is going to enter the leade.
Given a fixed powder charge, a load seated onto the lands will generally be higher pressure for the velocity than the same load with the bullet seated off of the lands.
Depending on where your charge is at (min/max/in-between) and what powder you're using the pressure spike can be small or large. When these guys are brewing up their benchrest loads they're not looking for max velocity, they're looking at max accuracy for their particular rifle's barrel which is not necessarily up near the top end where you'll start seeing high pressure.
For my hunting and varmint loads, I prefer to stay back off of the lands by at least 0.025" or more (it depends on each load for each rifle). I shoot year-round with the same loads from +90° to -20°F which already causes enough of a pressure/velocity fluctuation plus I'm wanting as much velocity/energy as I can get.