VLD's typically like to be jammed. I would start at say .010" and move toward .020" in. Let me know as I am going to be trying this same combination myself soon. The 216gr clinch river pills are too hard to come by, so bergers may be what I use.
You try to get closer to the target,..and I keep trying to get further away.
I just started shooting the 210 VLD's in my .300 Weatherby 5/5 Pac Nor 25.5 in .925 turn neck chamber. I shoot them at 300 yards and the last time to the range I shot 3, 3 shot groups all were under 2.00 inches. This was on a hot day (slight boil mirgae) and I think I am responsible for at least 1/2 inch of the dispertion.
I shoot 80.0 of 7828 right on the lands and grooves, mabe .0010-.0050 into them, it is hard to tell with the very shallow lead in my throat.
I am going to try Retumbo and H1000, I think those powders would work well in your 300 UM as well. I think 7828 would be a little slow with this bullet in you rifle, it is mine.
I loaded 30 rounds last night same load, except 15 or .010 shorter than the above load and 15 more are .010 shorter than that.
USMC Scout Sniper 88-94
Instructor 1st. Mar. Div. SS school 91-94
I also have some 210 VLDs to try. I have a proven sub MOA rifle. 700 with a 28" #4 Shilen select match bbl. I've had plenty of success with the 200 AB and 180 Scirocco. I will be trying H1000, Retumbo, Re25, WC 872, US869.
I'm thinking the first 2 will be what I end up with and possibly the Re25 as it has been a proven, repeatable tack driver with the Scirocco and AB bullets.
I may also try VV N165 and N560 since I have plenty on hand. I will start with bullets touching the lands.
I was going to try seating depth using the berger 210. How do you know when you have seated the bullet close to the lands or into the lands?
I am sure that there are many tools that work well for this. I use a Stoney Point (now owned by Hornady) OAL guage and a Stoney Point bullet comparator. They are very easy to use and seem quite accurate with a little practice.