Using a once fired, deprimed, non-resized case that holds the bullet reasonably snug, I closed the bolt (fully)& pushed the bullet into the lands. Easing the shell back out & measuring, I get 3.44-3.46 OCL (with a few different bullets). Factory Federal Premiums (with Nosler 180's) measure 3.31 OCL. Hornady manual says 3.34 OCL for all their 180's.
The canelure of the Speer, at 3.45 OCL is .13-.14 above the case rim, & there's no way a cartridge of that length will fit in the magazine (Browning A-bolt). Is an OCL of 3.39-3.4 (backing off the lands .05) in the ballpark for this bullet? (I don't have a Speer Manual). At that length, I'm not sure that the cartridge will fit the magazine, but any shorter seems like an awfully big "jump" for the bullet. Is my measuring process flawed?
BTW - the Hodgdon site lists 69 - 74 grs. IMR 4831 for a 180gr bullet. Is that load appropriate w. the Grand Slam 180 gr.?

Here is the speer data from the #13 manual.

Win cases
CCI-250 primers

IMR-4831 Powder

Starting load 69 grains velocity 2789
Max Load 73 Grains (compressed) velocity 2951

I would not worry too much about bullet jump at first. Your rifle might like the bullet a long way off the lands. I would if it was me pick a length that will function through your mag and begin working on a load like say 30-40 tho off the lands if possable and work up with powder slowly and then once you see deicent groups you can try to fine tune with distance to lands or increasing or decreasing powder charge or both,

Thanks for the data Hipster - - what is the COL that is specified for the 180 Grand Slam in the Speer manual? - - I'll just start there & mess with it if the load shoots halfway well.

Speer lists col at 3.285"


Good luck finding a good shootin load.

Thanks!