How much freebore for the 6BRX??
- Thread starter Raptor
- Start date
halfmoanut
Silver $$ Contributor
104 is the most popular.
Before I had my 6BRX reamer cut I called Dave Kiff, told him what my first bullet choice was ( 107 SMK) and how I wanted to seat it in the case neck, ( just a few thousandths in front of the neck/shoulder junction), and within a very few minutes he had the dimension, .077" of freebore. Keeps the bullet in front of the donuts if/ when they should form and lets me touch, or even slightly jam, with close to full bullet/ neck contact. If I want to seat them deeper with some jump, I just make sure they are donut free, if not, the donuts will be removed before loading. That will only be something to consider until enough erosion develops anyway.
Dave's .104 FB reamer was designed for the original thin jacket 105 vld (hunting). It puts a loaded round touching with the bullet base .010 out of the neck shoulder. The 107 SMK, Burg 108 has more bearing surface. Optimally it needs more room. .125 FB. I'm not sure about the Berger 105 hybrid.
Robert,
Is the other half of the question the kind of bullet I would be shooting?? If so I guess I don't really know what it will like.
I would like to shoot the 107 SMK or maybe the AMAX. I will use it for local tactical matches. However if it likes the Bergers or the scenars then I guess I would go with them.
Thanks for the replys so far, it gives me a pretty good idea of what I am going to need.
Is the other half of the question the kind of bullet I would be shooting?? If so I guess I don't really know what it will like.
I would like to shoot the 107 SMK or maybe the AMAX. I will use it for local tactical matches. However if it likes the Bergers or the scenars then I guess I would go with them.
Thanks for the replys so far, it gives me a pretty good idea of what I am going to need.
rcw3
Site $$ Sponsor
Raptor
Maybe my earlier post was a tease (and I apologize for that) but actually, the other half of the question is really the other 2/3 of the questions/assumptions. A freebore dimension in and of itself is of no value unless you know (1) what the max case length it's stacked on top of (in the case of a wildcat like a 6mm BRX that can vary because there is no standard for the max case, some use 1.570", some use 1.560", and I have seen as little as 1.555", and for the reamer I made up I used 1.563"); and the freebore selected also will necessarily depend on the selected throat angle since bullets will sit further out with a mild throat angle than with a steeper throat angle.
If you select a ".119" freebore, but put it on a max case of 1.555", that's the same as a .104" freebore on top of a 1.570" max case length.
Correspondingly, if you have a one and a half degree throat angle with around a .130" or so freebore, you will find that the bullets hit the lands in about in the same place if you have .110" freebore with a 1 degree 10 minutes throat angle. Now most use a one and a half degree throat angle on the 6mm BRX, but I have seen some with a 3/4 degree throat angle and some with a 1 degree throat angle, etc.
The real questions with the BRX are:
What max case are we working with?
What throat angle are we working with?
Then what freebore is right so that the bullet you have will sit where you want it to sit (assuming a freebore diameter like .2435" because the freebore diameter also can change where the bullets engage the rifling - like the .308 Win SAAMI has a .310" dia. freeebore vs a lot of match .308 Win reamers that use a .3085" dia. freebore and that makes a big difference where the bullets hit the lands).
Robert
Maybe my earlier post was a tease (and I apologize for that) but actually, the other half of the question is really the other 2/3 of the questions/assumptions. A freebore dimension in and of itself is of no value unless you know (1) what the max case length it's stacked on top of (in the case of a wildcat like a 6mm BRX that can vary because there is no standard for the max case, some use 1.570", some use 1.560", and I have seen as little as 1.555", and for the reamer I made up I used 1.563"); and the freebore selected also will necessarily depend on the selected throat angle since bullets will sit further out with a mild throat angle than with a steeper throat angle.
If you select a ".119" freebore, but put it on a max case of 1.555", that's the same as a .104" freebore on top of a 1.570" max case length.
Correspondingly, if you have a one and a half degree throat angle with around a .130" or so freebore, you will find that the bullets hit the lands in about in the same place if you have .110" freebore with a 1 degree 10 minutes throat angle. Now most use a one and a half degree throat angle on the 6mm BRX, but I have seen some with a 3/4 degree throat angle and some with a 1 degree throat angle, etc.
The real questions with the BRX are:
What max case are we working with?
What throat angle are we working with?
Then what freebore is right so that the bullet you have will sit where you want it to sit (assuming a freebore diameter like .2435" because the freebore diameter also can change where the bullets engage the rifling - like the .308 Win SAAMI has a .310" dia. freeebore vs a lot of match .308 Win reamers that use a .3085" dia. freebore and that makes a big difference where the bullets hit the lands).
Robert
Robert,
Thank you for the explanation. I am new to the 6BRX and know very little about it. I am going to check with my smith this next week to see what he has (If he has) for a reamer.
I was trying to find out as much as I could so I would have an idea of what I needed. If he would be buying a reamer I wanted to have an idea of what would be the best way to go or if I bought a reamer what would be the best.
I plan on using the new Lapua brass since I don't have any and will be buying it. I also plan on doing a "Light" neck clean up so figured close to a .270 neck.
I have no idea on throat angle so I guess any advise on how to spec this or any other ideas as far as the rest of it would really be helpful. Once again thank you for all your help!!
Thank you for the explanation. I am new to the 6BRX and know very little about it. I am going to check with my smith this next week to see what he has (If he has) for a reamer.
I was trying to find out as much as I could so I would have an idea of what I needed. If he would be buying a reamer I wanted to have an idea of what would be the best way to go or if I bought a reamer what would be the best.
I plan on using the new Lapua brass since I don't have any and will be buying it. I also plan on doing a "Light" neck clean up so figured close to a .270 neck.
I have no idea on throat angle so I guess any advise on how to spec this or any other ideas as far as the rest of it would really be helpful. Once again thank you for all your help!!
rcw3
Site $$ Sponsor
Raptor
Check out my web page on the BRX - it has reamer prints on it and some info.
http://www.6mmar.com/6mmBRX.php
If you need to know where a bullet sits in the neck with one of those reamers I can queue one up and post a digital picture to show right where it sits in the neck (i.e. I have a case with a slit up the neck so you can see exactly where the bullet sits).
Personally I think the .104" freebore is a little short (with a 1.570" max case and a one and a half degree throat angle).
Robert
Check out my web page on the BRX - it has reamer prints on it and some info.
http://www.6mmar.com/6mmBRX.php
If you need to know where a bullet sits in the neck with one of those reamers I can queue one up and post a digital picture to show right where it sits in the neck (i.e. I have a case with a slit up the neck so you can see exactly where the bullet sits).
Personally I think the .104" freebore is a little short (with a 1.570" max case and a one and a half degree throat angle).
Robert
tclaunch
Silver $$ Contributor
I`ve spent/wasted some coins playing with freebore on the 6BRX. I bought into Kiffs 104" and his Crone version of the cartridge case length that required me to trim Lapua 6BR cases .015" before my bolt would close on a 6BR case. That reamer was a total waste of money. I now have 3 others which are a marked improvement. I have tried from .132" FB to .170" all with a 1.565" to 1.570" chamber length. I`m happiest with a .140" for what I consider the most universally suited length. I did find worrying about freebore is also kind of overrated.
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