Free bore for the 230 Berger

[Edd]

So you took into account the transition from the case mouth to the beginning of the parallel freebore, the length of the freebore, and the transition from the end of the parallel freebore to the point where the bullet will contact the rifling ie the length that it takes for the diameter in the throat to reduce from .3092 to .308?

Yes

If you change that .3092" to .3085" , and I think you should, the freebore length would change to .1794".

 

[NEMTHunter]

30-338 Lapua with that much room you could go with a free bore of .260, That seating the bearing surface about .269 into the neck and that puts you at about 3.843 COAL. Thats close to the max of 3.850 you gave. Maybe you want a little shorter free bore.

 

[NEMTHunter]

With the RUM you could go with about a .270 free bore.

 

[cjuve]

This is for the 30-338 Norma.
If you have the standard case length of 2.492, Then that means you should be able to go with a .280 free bore and have a COAL of about 3.63.

Thats only seating the bullet's bearing surface .250 into the neck.

Yes, I have plenty of room in the mag to go what ever length that I want, part of the reason that I went with the Norma. Nailing down the exact freebore length is probably an exercise in futility anyway since there is no guarantee that the bullet will want to be seated there. I am just trying to give myself the best blend of capacity and options to shoot other heavy bullets without stretching it to far.

 

[L.Sherm]

I just looked at a P.T.G reamer print and it has .214 freebore I think in the .225 -.230 will suit you.

 

[NEMTHunter]

Got you. All the free bore length I gave will come close to maxing out the magazine other then the .300 Norma mag.

The hybrid bullet does not mind a jump. BUT with the free bore given you will not need to jump.

 

[L.Sherm]

I dont understand Dave's measurements on the print you posted with a contact at 2.70+ using a 230 otm they have a .549 bearing surface longer that the hybrid. And it states its seated with the start of the boatail at the neck shoulder junction

 

[cjuve]

I dont understand Dave's measurements on the print you posted with a contact at 2.70+ using a 230 otm they have a .549 bearing surface longer that the hybrid. And it states its seated with the start of the boatail at the neck shoulder junction

Are you talking about Edd's calculations? If so his calculation takes into account not just parallel freebore but also adds in the transition dimensions for the case mouth to parallel freebore and parallel freebore to bullet contact. Basically the 2.70+ distance is from bolt face to where the bullet would contact the rifling at a .308 diameter. These lengths are not directly shown by my prints, this is a lot of the reason that there is a lot of confusion around freebore. JGS shows more of these dimensions when they give you a print.

 

[L.Sherm]

Yeah, Dave comes up with a .130 freebore with a otm.
Not only do I like JGS reamers I like there prints also.

 

[NEMTHunter]

I use Manson reamers. I do like JGS print's though.

 

[cjuve]

Yes

If you change that .3092" to .3085" , and I think you should, the freebore length would change to .1794".

So given a bullet with a bering surface length of .549 and a neck length of .323 I would need to have a parallel freebore length of .1766 to seat the bullet with the base of the bering surface at the neck shoulder junction?

What angle do you use to calculate the distance from the case mouth to the beginning of the parallel freebore? I don't think I have ever seen that on a print just a dimension for the lead.

 

[cjuve]

Yeah, Dave comes up with a .130 freebore with a otm.
Not only do I like JGS reamers I like there prints also.

Yeah that is why I sent some dummies to him I thought that dimension was short of what it should be.

 

[L.Sherm]

His 30-338 print makes more since.

 

[NEMTHunter]

This is a Manson reamer drawing.