Chamber vs Resizing measurements...

[Potenza]

Hello all, I have a project to neck down a 6.8 Western cartridge to 6mm and I'd like to know some details regarding the dimensions of the resized cases versus the chamber. This rifle will be used for whitetail hunting and also a little target shooting, but not much. I know that dimensions that are too tight can cause problems. I was wondering if a 0.001-0.0015" clearance at the base and 0.003" at the shoulder would be sufficient, I also intend to turn the necks. Let me know what you think of this and what might be better. Thanks for the help.

 

[DaveTooley]

These are the bare minimums that I've used for target rifles in a perfect world.
Chamber +.003 over brass diameter @.200 line
Chamber +.004" over brass at the shoulder
Resize reamer -.003" under finish reamer.

For a hunting rifle I'd add .002" to the finish reamer and .001" to the resize reamer
Too tight and you have nothing but problems.
A little loose and no one knows.
Have both reamers made at the same time.

 

[Bill Rodolph]

I think I would try something a little different. Get a 6.8 full length bushing die and use 6mm bushings. Then have the neck diameter on the chamber reamer ground to whatever dimension fits your needs.

 

[Potenza]

These are the bare minimums that I've used for target rifles in a perfect world.
Chamber +.003 over brass diameter @.200 line
Chamber +.004" over brass at the shoulder
Resize reamer -.003" under finish reamer.

For a hunting rifle I'd add .002" to the finish reamer and .001" to the resize reamer
Too tight and you have nothing but problems.
A little loose and no one knows.
Have both reamers made at the same time.

Thank you for your reply. You mentioned a 0.003 difference between the chamber reamer and the resizing die for target shooting, and slightly more for hunting. I have a question: will a case resized in a die to be 0.003 smaller actually be 0.003 smaller when it comes out of the die? Isn't there some kind of spring effect involved? Excuse my english I'm french Canadian.

 

[DaveTooley]

Thank you for your reply. You mentioned a 0.003 difference between the chamber reamer and the resizing die for target shooting, and slightly more for hunting. I have a question: will a case resized in a die to be 0.003 smaller actually be 0.003 smaller when it comes out of the die? Isn't there some kind of spring effect involved? Excuse my english I'm french Canadian.

There is spring back. When fired and when sized. Using .003" is a very skinny tolerance. Like less than .001" clearance. In hindsight I was lucky. I have no way of knowing if my reamer maker friend fudged things to keep me out of trouble. Also you have to FL size from the first firing. If the brass work hardens at all at a larger diameter you're screwed. Sizing will get it back in the chamber but not out.

 

[Taylorbok]

The only case I've done a resize reamer and built my own die for I went .004" under. It's a hunting rifle, shoots great, no clickers.

Since its a hunting rifle and you aren't improving the case (it's just a straight neck down)
I agree with @Bill Rodolph get a bushing die and just use a SAAMI print and order the reamer neck to your desired diameter.

If you wanted before you order the reamer cast the die with cerrosafe and take some very careful measurements to see how they align with what the reamer print is.

 

[WSnyder]

I think I would try something a little different. Get a 6.8 full length bushing die and use 6mm bushings. Then have the neck diameter on the chamber reamer ground to whatever dimension fits your needs.

That’s exactly what I did for this cartridge. I used SAAMI 6.8 Western specs and modified the print for a 6 neck. I used a Redding Z Series 1” bushing die for sizing. The larger Z Series seems to work a little better sizing the larger diameter bases of the WSM cartridges. I’d have to check if I went a bit larger at the .200 line or not. I think I went a bit larger but can’t recall at the moment.

 

[Potenza]

The only case I've done a resize reamer and built my own die for I went .004" under. It's a hunting rifle, shoots great, no clickers.

Since its a hunting rifle and you aren't improving the case (it's just a straight neck down)
I agree with @Bill Rodolph get a bushing die and just use a SAAMI print and order the reamer neck to your desired diameter.

If you wanted before you order the reamer cast the die with cerrosafe and take some very careful measurements to see how they align with what the reamer print is.

I've been considering this method: instead of molding the die, perhaps I could use a 6.8mm fired case and resize it in the new die. That way I'd have the case with its spring back. But measuring that with such precision afterward can't be that simple. To take measurements exactly at .200 line ans shoulder..! It's not a problem for me to make a perfect sizing bushing die and the bushing needed, I'm equiped in tools and material for that, reamer in less.

 

[Potenza]

That’s exactly what I did for this cartridge. I used SAAMI 6.8 Western specs and modified the print for a 6 neck. I used a Redding Z Series 1” bushing die for sizing. The larger Z Series seems to work a little better sizing the larger diameter bases of the WSM cartridges. I’d have to check if I went a bit larger at the .200 line or not. I think I went a bit larger but can’t recall at the moment.

Wow, I thought I was the first to use the 6.8 for that, loll. How many step down with the neck bushing did you do to reach 6MM?

 

[WSnyder]

Wow, I thought I was the first to use the 6.8 for that, loll. How many step down with the neck bushing did you do to reach 6MM?

A bunch of steps to bring it down. I used Alpha brass. Alpha brass is really soft in the shoulder and it’ll crush if you’re not careful. I’m using a combination of a John Bunch form die and a traditional bushing die to bring it down. I’m not the first to do it either. There’s another guy I came across and have discussed it with that started his project about the same time. I believe AWheeler has had a hand in that one. As an aside when I initially talked with JGS there were no publicly released reamer prints at the time, just the print of the other guy I mentioned. We discussed dimensions but did our own thing at the time. I need to touch base with him again.

FWIW a 25 Western has been done as well. That print is/was not public either.

 

[Taylorbok]

I've been considering this method: instead of molding the die, perhaps I could use a 6.8mm fired case and resize it in the new die. That way I'd have the case with its spring back. But measuring that with such precision afterward can't be that simple. To take measurements exactly at .200 line ans shoulder..! It's not a problem for me to make a perfect sizing bushing die and the bushing needed, I'm equiped in tools and material for that, reamer in less.

If you use brass from another chamber that was poorly cut you could end up with some misleading numbers.