I recently acquired a CZ 550 Safari American that has a SS Douglas barrel in 458 Lott. Headspace is perfect--bolt completely closes on a go gauge while it stops after 20-30ish degrees of bolt closing on a no go gauge. I was checking bullets for seating depth and found that all Hornady 500 grainers: RN, DGX, and DGS have about 1/2" of freebore when seated to the cannelure. The 500 TSX had about .325 freebore when seated at a groove providing .450 to .500" of bullet seating in the neck.

Are Lotts typically chambered with that long of a throat?

I believe it should be one caliber of throat. So, .460 from the end of the case mouth to the start of the lead angle. The lead is probably 2 or 3 degrees so the entire lead would be from .130 to .200 inch long depending on the lead angle and rifling depth used.

Pretty long when compared to other calibers. About the same as other calibers or maybe even pretty short when you consider the bore diameter that your dealing with.

Thanks--I just have never seen one with that much throat. Not even my 450 NE.

458 Lott is spec'd by SAAMI and it has a .190 throat and a 2 degree lead; BUT if they copied the 458 win chamber, it has a 29 minute 30 second lead, which makes for a very long throat. They do that to reduce pressure in hot climates, so your chamber is not abnormal; fire away.
Look at a Ruger 458 chamber; there is no rifling for a very long ways.

Yeah, SAMMI shows it as having a a HORRIBLY short throat. I suppose in single shots and doubles if you were using modern double dimension bullets they would be fine. In modern, magnum bolt guns where you want 3.5 inches OAL for feed and magazine stacking reasons you would probably find that you would have to push the bullets pretty deep into the cases to stay off the lands and grooves with old fashioned bullets. That problem would be eliminated with double diameter bullets or bullets with long ogives. I generally put one caliber of throat including the lead in chambers that I cut unless the customer wants to special order a reamer with a short throat. A lot of reamer companies also use that rule of thumb as standard unless otherwise specified or for cartridges that traditionally have very squat bullets. I do notice that a lot of modern 458 caliber bullets today are double dimension. The entire front half or even 2/3rds of the bullets generally will measure .452 with the driving area at the back measuring full diameter. Bullets of this design would function just fine in a short throated gun.

SAMMI 458 LOTT by Rod Henrickson, on Flickr

Thanks again. Hopefully will shoot this weekend. I have it in a B&C aluminum bedding block stock since the barrel does not have a lug and I was leery of shooting it in the factory wooden stock. The barrel contour appears to be Douglas' 458 contour and is 26" long. With a Leu 1.75x6x32 mounted it comes in at about 10.25 lbs.