Gunsmiths when chambering for the 300 Remington ultra mag how much throat do you put?

To the ogive, with the bullet seated out where the bullet of choice should be. I just finished one that took a .250 length throat. (I cut all my throats separate). Had to go with a Wyatt's extended RUM box but that's what you need to do to utilize that size case.

The throat on a SAAMI spec reamer is integral with the body of the reamer. If you want one shorter, the reamer needs to be re-ground or custom ordered. If one longer is required, a separate throating reamer can be used. I often throat using one to the spec the client specifies with a loaded dummy round

The reamer I am useing has NO throat. I'll cut it to SAMMI specs. Thanks guys.

DITTO on the Wyatts extended mag box. I have used them & like them.

DH
Perhaps I'm a Luddite, but (as a shooter) I don't get all wound up about throat LENGTH, but I do get fussy about throat DIAMETER.
I feel that you will lose a lot more having a throat that's to large than you will with one that's to long.
The only downside to the kind of throat I like is that you can sometimes pull the bullet out of the case during extraction

The throat length has a huge affect on chamber pressure.

I constantly refer to the throat as the "birth canal". What happens there will influence the path the bullet takes for the rest of it's rather short life.

All of my throating reamers are minimum leade (1.5 degree), minimum diameter (.0005 over bullet) reamers. But the length has to be sufficient to allow longer seating in order to make good use of case. The tighter throat dimensions helps keep the lighter, short bullets on the straight and narrow.

quote:

"birth canal".

A excellent way to describe it indeed!