I'm getting things together for a .300 Win Mag build.  Nothing fancy, long action LH 700, Krieger, McMillan, Badger, etc.  Not trying to reinvent the wheel.  

I won't be shooting factory loads at all, and I'm wanting to know about throat leade for seating the bullets out to maximum that will fit in a BDL mag box.  Anyone have any experience here?  

Also, I won't be shooting bullets lighter than 200 grains, and it looks like I can get away with 1-10", but I thought maybe 1-9" in case I want to shoot 215's-230's.  Again, I'm interested in anyone that has experience here and curious as to velocity with the heavier .30 cal bullets.  I'd like to see 3000fps with 200/208/215 grain bullets.  

Planning on a 28" barrel plus TBAC Ultra 9.  Heavy, but should be pleasant to shoot.

It really depends on how your chamber is cut, but most competent gunsmith should be able to cut your chamber to shoot what ever you want.

Had my 26 inch 1:10 krieger cut for a 208 amax at 3.62 (AI MAG length ) on top of 77.7 of retumbo,  it's running about 2915.

I use Berger 230 grain Hybrids at 2850 fps and seated to 3.615,  which is .015 off the lands in my 1/8 twist  barrel.  I needed a longer magazine and went with an Accurate Mag 3.850" length setup.  You could get by with a 3.715" though.

Send in some dummy rounds and have your barrel throat cut to fit.  

Run the ballistics numbers and you will be impressed with this load.  Also, I have pushed velocity to almost 3000 but pressure was high. 2850 is a fairly easy load to get to with 76 grains of H1000 (in my barrel).

Since you are building it, your mag length will eventually determine your COAL.  Reliable feeding would be the only hold up in an untested setup.  Either way I'd have the barrel cut to accept the longest and if you have to choke it back for feeding a bit, or hand load wouldn't be big deal if you are using it for hunting or long range shooting.

I doubt you'll get 3k with heavies without some pressure signs, but you should be able to get it a little faster with accuracy than factory loads but you are tuning all the variables.

good luck

I just decided to go with an action from GAP and eventually go with .300 Norma Mag.  230 Berger Hybrids at 2900+ should do what I want.

I was loading 208 A-max bullets nearly .100 over COAL and they fed in an AI 300wm magazine without issue.  I did have to trim the feed lips back about .150" so that it would let go of the case sooner and not wedge the round between the magazine/ feed ramp/ top of the chamber, but that was probably specific to that rifle. It was a savage with CDI bottom metal.