The 6.5 Something NOW Has A Name!

[GLTaylor]

6.5 BLASER MAGNUM IMPROVED!

Got a drawing from JGS yesterday. Parent cartridge is a 7mm Blaser Magnum necked down to 6.5mm with 40 degree shoulder. The drawing is a PDF file so I can't manipulate it, copy or share it. Wish I could! Case capacity should be about 76+ grains. It's basically a 257 Wby Mag minus the belt and no radiused shoulders.

I've got some questions, cause I've never done this before. I'm mainly interested in how much free bore/throat to specify. I plan to shoot Hammers in a 1:7.5 twist barrel, but want to be able to shoot both Hammer Hunters and Absolute Hammers. I' guessing the throat will need to be upwards of 150 thousandths, as that's where my 338 Sherman ended up, but I really have no idea.
Also, what about body taper? How much to specify, and why?

OK you gunsmiths and gurus out there. Give me a hand with birthing this new baby!

Thanks

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[dok7mm]

Set up a dummy round with BS/BT positioned where you want it. JGS will take it from there.

You might make a dummy for potential bullets you might want to use and take an average of FB.

 

[tobnpr]

^^^
This.
You want to get neck diameter and desired freebore/leade angle, etc. all correct in the reamer geometry instead of monkeying with throaters and neck reamers later. This way you know the chamber will be exactly what you want.

 

[GLTaylor]

I finally figured out how to attach the cartridge drawing.
All of the Ackley Improved cartridges I have use very little case taper. If I am reading this drawing right, it has quite a bit of taper?
How much taper is appropriate and how much throat is "normal" for 120-140gr mono bullets of a VLD style?

 

[DJ Fergus]

I'm waiting to hear an answer to this myself. I don't shoot that bullet so I wouldn't be able to even guess.

 

[can1010]

what is your goal with this? not trying to be a smart EDITED but having to get custom dies for just an angle change from 30 to 40 degrees. that drawing is just a neck down and angle change with all other dimensions left original. I would leave it 30 degrees and use a bushing die and change bushings or go full blown wildcat and order custom dies.
you can push the shoulder back to 40 giving a longer neck and blow the body taper .010-.015 more that will put you in the 86-88 gr. capacity the original is 87 gr.
I believe norma is the only supplier of blaser brass are you sure you want all your eggs in that one basket

 

[David Emerson]

I would leave as is. I like the throat and taper as you have plenty of volume and it should feed good. I made a 6.5x308 norma some years ago 30 degree. It had a .150 throat and the bullets had to be waaay out there to get to the lands. Being you are shooting hammers how about call it the 6.5 Thor? But I agree with can1010. I would have left the shoulder at 30 degrees.

 

[GLTaylor]

The goal is a case approximating the 257 Wby Mag without a belt and radiused shoulders. So far, input suggests blowing walls out for less taper, 40° shoulder to minimize case stretching, changing the throat angle from 45 to 30° to reduce throat erosion, throating to 180+ thousandths and keeping a long neck. Nothing remarkable here. Just an old man's winter project. Plus, it keeps me out of trouble! By the way, I'm hoping for case capacity around 80 grs

 

[GLTaylor]

I would leave as is. I like the throat and taper as you have plenty of volume and it should feed good. I made a 6.5x308 norma some years ago 30 degree. It had a .150 throat and the bullets had to be waaay out there to get to the lands. Being you are shooting hammers how about call it the 6.5 Thor? But I agree with can1010. I would have left the shoulder at 30 degrees.

That's still a possibility. Nothing cast in stone yet
How is case stretching with 30° shoulder?

 

[David Emerson]

Your necks will grow a little at 30 but not bad. Something about 30 degrees and accuracy. Look around. They feed better too. When PO made the 40 degree he was after max volume increase.

 

[P7M13]

I would not call it improved at a 0.050 body taper. Call it the 6.5 BMI (body mass index / barrel metal incinerator) 'cause its going to test whether your shoulder is made of jelly and toast the barrel fast!

 

[P7M13]

If you haven't read it yet, here is an excellent article, on this site, written by Bob Jourdan.

Pressures, Case Strength and Back Thrust

Pressures, Case Strength and Back Thrust By Bob Jourdan ©Copyright 2010, Precision Shooting Magazine All handloading manuals take safety very seriously. They cover most of the hazardous points in reloading ammunition in an effort to keep a...

www.longrangehunting.com

 

[can1010]

on my quickdesign.
6.5-257 Roy 86.6
7mm Blaser 88.6
6.5-7mm Blaser 87.8
now quickdesign is usually about 1-1.5 gr over on capacity so you are right there, now you have to decide on how far you want to go simplicity or expensive wildcatting aint cheap

 

[GLTaylor]

on my quickdesign.
6.5-257 Roy 86.6
7mm Blaser 88.6
6.5-7mm Blaser 87.8
now quickdesign is usually about 1-1.5 gr over on capacity so you are right there, now you have to decide on how far you want to go simplicity or expensive wildcatting aint cheap

Thank you! At least I'm in the ball park of where I wanted to go. Straighter case walls also reduce back thrust as Mr. Jourdan pointed out.