6x47 freebore

[mikeymike]

Hello all,
What freebore are you guys using for the 115 JLK's and Burgers in your 6x47 Lapua's?? I am going to buy a 7.5 twist barrel and my reamer is a .104 freebore. Is this enough?? Thanks for any info you can give me. Mike

 

[rcw3]

Mike

Asking what the proper free bore length is without telling us what the throat angle is makes for an open ended question that no one can answer. You also have not said where you want the bullet to sit. If your desire is to have the bullet sit so the junction of the boat tail and bearing surface of the bullet is just ahead of the neck and shoulder of the case then you need to say so.

The other issue is who will be making up your reamer? If it's a maker like JGS whose reamers run very true to their prints and are very exact dimensionally, then I can get you very very close to where you want to be, if you tell me where you want to be. If it's a maker like Pacific Tool, then you have to leave some margin for error because their reamers seem a little loose to their prints.

A .104" free bore is on the short side if you intend to use a one and a half degree throat angle with the reamer and want the bearing surface of the bullet ahead of the neck and shoulder of the case (i.e. to avoid any potential donut). If you run a one and a half degree throat angle I would run with a free bore around .140" with a JGS reamer with those bullets. If it is a steeper throat angle, you will need a longer free bore and if it is a shallower throat angle you will need less of a free bore.

With a JGS reamer with a one and a half degree throat angle and a .140" free bore, your OAL with a JLK 115 gr. VLD hitting the lands should be around 2.754" and with a Berger 115 gr. VLD, it should hit the lands around 2.786" (and both of those bullets are nicely positioned in the case at those OAL's. If I were shooting those 115 gr bullets in that cartridge I would run with the .140" free bore.

Robert Whitley

 

[mikeymike]

Hi Robert,
Thanks for the great info. My reamer is a Pacific with 1-30 angle. I loaded up a dummy and you are right on, the bearing / boat tail junction is right at the neck / shoulder with a real soft jam. I thought it may be to short and with your explanation I now have a better idea of where she should be. Thanks for the help. Mike