How about this one.
6.5x55 slightly short chambered and then using a 6MM BR Norma reamer to clean out the chamber to a 6.5BRx55.
30 degree shoulder, minimum case taper, nice long neck,
Fireform 6.5x55 brass with projectile stuck in the lands.
Give a few grains extra capacity
will still feed from the magazine if required.
Using lapua brass you can load it nice and warm as stil have plenty of safety margin.
FLS die can be made using a 6mmBR roughing or sizing reamer.
Can use a Hornady new generation 6.5x55 seater- add a Hornady "microjust" top and ream out the sliding sleeve to suit.
6.5x55 ammo can be used in it to fireform brass.
sort of an easy Wildcat to make and will run with a 40 Deg AI and a 6.5x284 quite easliy and burn less powder and have a longer barrel life.
I'm planning mine for the Tikka 695 master Sporter.
The same priciple has been used to creat a .243 TBR and then neck it upto 6.5mm
(snip from 6mm BR.com)
http://www.6mmbr.com/BlogSept2005.html
WILDCAT DEN--Fireball's "Tall BR": WarrenB ("FireBall") has devised a simple way to improve the performance of the .243 Win: "I call this my '6mmTBR', which is a .243 with the long neck and 30° shoulder of the 6BR case. I simply took Lapua .243 brass and ran it into a 6mmBR body die to give the .243 a 6BR top end. The resulting cartridge is like a Tall BR, hence the 'TBR' name. I shoot the TBR in a Panda and it is incredibly accurate. Combine the TBR with a 70gr Nosler BT and you have an awesome windy-day Prairie Dog rifle. Or you could use it competition. At 600 yards, I think the TBR would give the 6XC, 6-250 and other mid-size 6mms a run for their money. And if you already have 6BR dies there are no tooling costs involved. Plus you get to use Lapua brass. The 6XC and 6-250 can't claim that!" [Editor's note--The TBR rivals the 6-284 with much lower brass cost.]
(endsnip)
LAter
p