I used a min spec short throated 300WM reamer and then sent a dummy in for the smith to cut the throat to. The rifle is a trued Rem 700 with the bolt sleeved and has a 10 twist 26 inch 5R benchmark. Im using PRVI brass, fed 215 primers and Retumbo. I don't remember if I used a Wyatt's extended box mag or not so you'll have to check the length of the mag in the rifle type you intend to build off.
Loaded with 215 bergers the COAL is about 3.642
Measured with a hornady comparator to the ogive it's 2.870, this 20 thou off the lands
77.8 retumbo gives 2910 fps at +4C
This shoots right at 1/2 moa from the bench
The chamber was cut for the 215's but a while later I came across some of the Hornady ELD-X 212's so I gave them a try too
Loaded with 212's the COAL is about 3.587
Measured with a hornady comparator to the ogive it's 2.871, this is 10 thou off the lands
I'm also using 77.8 retumbo and chronographed 2900 fps at 0C
This also shoots right at 1/2 moa
I use a magneto speed
Both rounds fit in the mag and both allow me to chase the lands when they erode and still have plenty of bullet bearing surface in the case neck.
Here's the great part, they both shoot to the same spot at 100 yards and there's no need to re zero. I entered all the 215 Berger load data info into my kestrel and tried it for the 212's. The solution for the 215's works perfectly for the 212's as far as I have shot them to which is 1577 yards.
I've no seen any pressure issues at those temps but I have not yet tried them on hot summer days.
Bergers stability program says I'm losing some BC with the 10 twist but a friend loved my set up and had the exact gun built by the same smith but with a 9.5 twist benchmark 5R. This time the smith throated it a bit longer - not sure exactly but somewhere in the neighbourhood of 20 longer than mine. He uses Winchester brass and a little less retumbo to get the same speed. Even with the projected loss of BC from my 10 twist our kestrels give us each a solution that is within .25 moa of each other out to the 1577 yards that we shot to.
I've used the 215's on game and they're great, I'm yet to try the 212's on game but plan to this season. They're easier to get and cheaper so I'm hoping they work well too.
I don't believe your over thinking things at all, it's way better to get exactly what you want the first time and know exactly what you're getting.
Since the 215 bergers and Broz's thread came out years ago depicting his results on elk my 7's haven't seen a lot of use hunting and my pile of 180 bergers is holding steady under the bench.
Hopefully this helps you out.
