Necking up 6br

[boltman223]

I have some questions about necking up a 6br and puting a 40° shoulder on it.

I'm wondering/thinking that the neck length would get longer since the diameter of the neck gets bigger and moves up the shoulder, but I've read that the necks actually gets shorter. Which way does it go?

I think I've also read that the overall length of the case shortens up when you form the 40° shoulder. is this correct?

 

[Grimstod]

When you form the 40d shoulder it will pull some of the neck into the body of the case.
But as a general rool when you neck up the neck does get longer as you said in your post.
Now the shortening you will see should be negligable since when you neck up there is less shoulder to expand and thus less shortening will take place.

The most shortening seen is when you neck down and expand the shoulder.

 

[boltman223]

When you form the 40d shoulder it will pull some of the neck into the body of the case.
But as a general rool when you neck up the neck does get longer as you said in your post.
Now the shortening you will see should be negligable since when you neck up there is less shoulder to expand and thus less shortening will take place.

The most shortening seen is when you neck down and expand the shoulder.

Great! That makes my life easier. Thanks for clarifying.

 

[JRS]

Necking up brass reduces neck length.

 

[Grimstod]

JRS you have it backwards. As you can see in this comparison between a 6BR necked up to a 30BR the neck does get longer. Looks like the neck gets 0.0548in longer.

 

[JRS]

Lapua cases shorten from approx. 1.550 to 1.520 after being necked up to 30 caliber.
"Mechanical neck-up processes reduce neck-length".

www.accurateshooter/cartridge-guides/30br/

 

[Grimstod]

1.550-1.520=0.030+0.054=0.024 longer.

 

[boltman223]

So I think JRS is saying that the overall length shortens even though the neck does get longe?

So if 6mm to 30 cal loses .030 will 6mm to 6.5 loose roughly .015 in length?

How much more will be lost going to a 40° shoulder?

 

[JRS]

The OAL is a bit shorter due to the reduction in neck length when necking-up. The neck length on my 25BR cases is a bit shorter than the neck length on the parent 6BR case, but, I don't remember the actual reduction in length.

 

[boltman223]

The OAL is a bit shorter due to the reduction in neck length when necking-up. The neck length on my 25BR cases is a bit shorter than the neck length on the parent 6BR case, but, I don't remember the actual reduction in length.

Do you have a print of that reamer?

 

[JRS]

Do you have a print of that reamer?

You can get a copy of the print from JGS. It is listed as the 25BR RS.

 

[boltman223]

So, I was able to answer one of my own questions... i found an expander I could use in my die.

necking up 35 rounds to 6.5 and 7mm I lost on average .010 on overall case length. I did not lose any neck length. I actually gained about .015 on the neck, maybe closer to .020. The neck length was a rough measurement with a caliper so I can't give an exact amount.

The only question left is how much aol and/or neck I will lose when fire forming the 40 degree shoulder. It would only be nice to know for my reamer specs.

 

[boltman223]

You can get a copy of the print from JGS. It is listed as the 25BR RS.

Is that print yours? They said the print was requested to be kept proprietary.