What would be the benefit of a tight chamber for this cartridge?
Would I have to order a custom reamer, according to the lapua brass I will use?
I guess the dies would be the standard ones?

As I understand ,the american companies are making the brass to the 308 head diameter [.473"] while the original and the europeans make the cases to .480". If you have .480 brass cut a .480 chamber and use .480 dies. A .473 case in a .480 chamber is not good for accuracy.

When Win first came out with the 6.5x55 in a fwt there were some problem with the chamber etc I don't think it was set up for the american round and they had to change that.

Any factory chamber will be big. It has to accomodate every brand of loaded ammo available. Not real good for brass life and accuracy. A good chamber cut for Lapua brass with a proper fit will make the Swede do more than it was intended for.

SO? What would be a good cut? Anybody have demensions.

There was an interesting post maybe a year ago and a fellow from Norway explained the different 6.5x55 dimensions IIRC they included Norwegian military, Swedish military and maybe civilian.The scandinavians then decided to sort things out and came up with a compromize- the 6.5x55SE. I think the europeans now have chambers and cases made to this standard and I would make on to that standard also.As for a throat ,personally I think throat diameter is as important as length but most of them are cut to fit the long 160 grain bullets and firing shorter 140 in such a chamber doesn't seem to hurt accuracy [certainly not mine].Anyway I think the best bullet is the 140 and twist for that 1 in 9" or 1 in 8".It has been called the ideal deer cartridge and I have to agree.

Buy a couple hundred Lapua brass. Take one and seat the bullet of your choice, or bullets in more cases, to a depth not more than the bottom of bullet to bottom of the neck. Send them to David Kiff. He will make a reamer to fit what you have: neck diameter, throat diameter and length, case dimensions, etc. You will get what you're looking for.

I have a 300m free rifle in 6.5x55 using a pre-64 M70 action and a 1-8 twist Hart barrel. I had a JGS floating pilot reamer ground for Laupa brass and throated for specifically for VLD bullets. If you would like to use the reamer, just drop me a PM.