Dummy rounds for barrel throating - Bullet jump or not?

[Bill2905]

I'm making dummy rounds for Shilen to use in a 6BR Norma barrel that I ordered. I determined that for the bullet I have chosen (68gr Berger Target FBHP), the overall length that places the heel of the bullet just above the shoulder/neck junction is 2.075 inches.

I'm leaning toward adding 20-30 thousands in length to allow for some bullet jump.

1) Does this sound reasonable?

2) Would any of you have the throat cut so that the bullet touches the lands at the deepest seating depth with no jump?

3) I'm not even sure how precisely they can cut the throat. Am I overthinking this and it doesn't really matter that much?

[azguy]

Couple years ago I built an Axis 11 223 for bench rest shooting. I used a CBI Match chamber. stainless heavy contour barrel. I spent a lot of time shooting test loads trying to find the right jump. I got the most accurate load using the OAL shown in the Hornady reload manual.

[sharpshooter]

Just have them make it a C.I.P. spec chamber and forget about it....

[charlie b]

I would talk to some people who have experience with the 6BR. If you are expecting bench rest competition accuracy you owe it to yourself to do some more research.

I know of several bench rest folks who seat their bullets into the lands a specific amount. Others have a very precise jump to the lands. All depends on the barrel, bullet and load.

Without any other information I would so as suggested above and have the chamber cut to std dimensions. There is a reason the mfg chose those dimensions.

[Robinhood]

I would talk to some people who have experience with the 6BR. If you are expecting bench rest competition accuracy you owe it to yourself to do some more research.

I know of several bench rest folks who seat their bullets into the lands a specific amount. Others have a very precise jump to the lands. All depends on the barrel, bullet and load.

Without any other information I would so as suggested above and have the chamber cut to std dimensions. There is a reason the mfg chose those dimensions.



Just have them make it a C.I.P. spec chamber and forget about it....

Done

[Bill2905]

Appreciate the feedback. Thank you.

[Nor Cal Mikie]

"have the chamber cut to std dimensions?" So, what is a std dimension?? Depends on who you ask.
I order all my chambers cut with ZERO FREEBORE!! Why? You start off loading 60 grain bullets, you find the sweet spot of seating depth.
Before too long the throat has worn (sooner than expected) and you can't get that same setting anymore. So, you're staring all over again from scratch.
I jam all my bullets .010 into the lands and I start off with the lightest bullets I can get my hands on. ( I strictly bench shoot)
As the throat wears, you adjust the OAL to keep the bullets in the jam. You go to heavier bullets as the throat wears.
You go with an "off the shelf" chamber cut and before too long, you're looking for another barrel cause the throat is too long from day one.
Bottom line??? Plan ahead and get what YOU WANT!
If you go long, you can't go back.
If you go short, you can always get a throating reamer and go longer.

[gbflyer]

I would set it up for your desired OAL for magazine fit if so confined or if that’s not a concern then set it up with the shoulder/neck junction as you stated. I wouldn’t want .030 added to that number. Maybe .005. As stated you’ll get to .030 soon enough especially with a Shilen.

[yobuck]

What’s wrong with having a gun for 60 gr bullets, and another gun for 100 gr bullets?
And would they both need to be 6mm?
I’d think most doing serious match shooting with a 6 BR would be using the heavier ones and not trying to tweak more life from their barrel.
Everything we do carries a price tag.

[Bill2905]

What’s wrong with having a gun for 60 gr bullets, and another gun for 100 gr bullets?
And would they both need to be 6mm?
I’d think most doing serious match shooting with a 6 BR would be using the heavier ones and not trying to tweak more life from their barrel.
Everything we do carries a price tag.

Yobuck, I agree. I selected a 12 twist barrel to handle lighter bullets for my intended shooting activity which is 100-200 yard bench shooting. I don't have easy access to 500+ yard facilities. I could have selected an off the shelf 8 twist barrel with longer throat for the heavy bullets but my research indicated that those are more appropriate for the long range game. If I ever find myself wanting to go longer some day, I will invest in a different setup and maybe a different cartridge too.

I started having second thoughts about adding more length for bullet jump and since then, several responses to this thread have concurred with this.