Can this be accurate? 300 Ultra OAL
 

Been trying out my new OAL gauge on my 300 RUM and it measures 3.795 bullet to the lands with a Swift Scirocco? .195 over the stated (published) OAL of 3.600 Most of my other rifles do not have this much difference. Does this make sense?

I was going to start by backing off .020 which would leave me at 3.775 OAL Should I begin to seat my bullets?

its called freebore, in high intensity cartridges (all weatherby's have it) they give the bullet a lot of jump to get higher velocity and keep pressure down, load to max mag length and have at it.
RR

RR Where would you start off the lands? .020, .050, 075?

whats your magazine max length? that's the deciding factor unless you wanna shoot single shot.
the closer you get to the lands the more your pressure will spike.
RR

Good Question. Just got done measuring it and seating bullets when I saw your reply. The magazine max is 3.680. So I'll be .115 off the lands. Don't think pressures should spike to much? I backed off on the loads a bit using IMR 7828. Thanks for the help

Siroccos like to jump too, so don't jam em anyway unless you want bad accuracy and high pressures.