I am working up a load for 7mm Rem. Mag. using Hornady 139 gn. GMX. I measured the overall length to the lands using a Hornady OAL gauge. I came up with 3.405" to the lands. How far off of the lands should I set the bullet?

No less than fifty

.050

You did not mention what rifle you have.
The round has to fit the magazine if you are going to use it as a repeater. Some 7mm Mags do not have a magazine that is 3.405 long.

I thought it should be .050 but the load listing showed the OAL as 3.29".

It's a Weatherby Vanguard. I already checked, there's plenty of room.

quote:

but the load listing showed the OAL as 3.29".

SAAMI max OAL? If the magazine box allows it then you will normally get better accuracy just off the lands. .05 is a good point to start. I normally start and finish around there. I don't spend a lot of time playing with OAL.

I have a couple 375 and larger that are set up with a full caliber jump.

Thanks for all the help.