Free bore for the 230 Berger

I am in the process of getting a couple reamers drawn up and was wondering what everyone was using for free bore for the 230 berger hybrid targets. The calibers in question are 30-338 Norma improved 33 degree, 300 RUM, 30-338 Lapua imp. 40 degree. All of my measurements and calculations put the correct free bore at approx. .225-.230 depending on the neck length required. After dealing with short throated magnums before a little extra free bore does not bother me and is actually preferred. If anyone has any suggestions it would be appreciated.

My son in law had a 300 Norma AI reamer done by JGS and I think it had .225 freebore for 230 hybrid.
I could look at the print if you'd like.
Sending in a dummy round with the base of the bullet just above the neck shoulder junction is the best way that's what he did.

L.Sherm said:

My son in law had a 300 Norma AI reamer done by JGS and I think it had .225 freebore for 230 hybrid.
I could look at the print if you'd like.
Sending in a dummy round with the base of the bullet just above the neck shoulder junction is the best way that's what he did.

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Thanks Sherm
I did send in a couple of dummies the 300 Norma actually came in at .230, what was odd was that the 30-338 came in at .200 and the 300 RUM came in at .140. I am sure that there is a chance that I jacked up the seating but based on the bullet specs and the fact that the neck lengths are all within .005 the free bore should not be that different. I think I may just make them all .230 and call it a day.

I know it's weird that way I had them build a 6.5x06AI reamer and the freebore came in at .130 with a 140vld and the same bullet in a 280AI was .180 go figure
Gotta be the difference in neck length.

If you are wanting the bullet to contact the lands when chambered, none of those dimensions are correct. For a 300 Norma you need a .180" freebore.

Every cartridge/bullet combo will be different, unless they have the exact same neck length. Some people's amount of freebore will differ from the next guy depending on if magazine length matters and/or if they want to shoot another bullet that may require more or less freebore.

The 230 Berger has a bearing surface that's .529 long. Take that number, subtract your neck length, then the left over number will be the amount of bearing surface above the case mouth, that will be the amount of freebore needed to touch the lands. You can add .010-.020 if you want the bearing surface above the donut area, or if you want to be .010-.020 off the lands at that overall length.

For example, the .300 RUM has a neck length around 0.306. Subtract that from the 0.529 of the bearing surface and you get 0.223. I would round up to 0.230 and that would be your ideal freebore.

Edd said:

If you are wanting the bullet to contact the lands when chambered, none of those dimensions are correct. For a 300 Norma you need a .180" freebore.

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Ok Edd you are going to have to school me, for the 300 Norma Improved 33 degree the neck has been lengthened .005 for a total .323 neck length. My intent is to seat the bullet so that the boat tail/bearing surface junction is at or above the neck shoulder junction. I am not concerned about COAL as long as I stay within the 3.850 mag box which should not be a problem.

cjuve said:

Ok Edd you are going to have to school me, for the 300 Norma Improved 33 degree the neck has been lengthened .005 for a total .323 neck length. My intent is to seat the bullet so that the boat tail/bearing surface junction is at or above the neck shoulder junction. I am not concerned about COAL as long as I stay within the 3.850 mag box which should not be a problem.

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I'm not sure what he's talking about. But for that cartridge, running the 230 Hybrids, I would want a 0.200-0.210 freebore.

Yep that's why .225 bearing surface above donut area.

Jud96 said:

Every cartridge will be different, unless they have the exact same neck length. Some people's amount of freebore will differ from the next guy depending on if magazine length matters and/or if they want to shoot another bullet that may require more or less freebore.

The 230 Berger has a bearing surface that's .529 long. Take that number, subtract your neck length, then the left over number will be the amount of bearing surface above the case mouth, that will be the amount of freebore needed to touch the lands. You can add .010-.020 if you want the bearing surface above the donut area, or if you want to be .010-.020 off the lands at that overall length.

For example, the .300 RUM has a neck length around 0.306. Subtract that from the 0.529 of the bearing surface and you get 0.223. I would round up to 0.230 and that would be your ideal freebore.

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Judd
Yes, this is the math that I was doing to get close, I figured that the dummies would get me to where I wanted to be but there was such a wide variance even though the prints that were sent to me had neck lengths within .005, the print on the RUM actually had a .320 neck length must have been the brass that I sent in.

cjuve said:

Ok Edd you are going to have to school me, .........

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Post your reamer print and I will.

He doesn't have a reamer print. That's why he is asking what freebore he should run. The only way to figure that out is to seat the bullet so the bearing surface is at the neck/shoulder junction and measure the remaining bearing surface above the neck, or to do the math like we just did.

Edd said:

Post your reamer print and I will.

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I don't have a finished reamer print yet just one that we were working with

Jud96 said:

He doesn't have a reamer print. That's why he is asking what freebore he should run. The only way to figure that out is to seat the bullet so the bearing surface is at the neck/shoulder junction and measure the remaining bearing surface above the neck, or to do the math like we just did.

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He wouldn't know all the numbers he has quoted if he didn't have a print of some kind.