Chamber questions

[afret]

With this info which one would be better for shorter FB bullets? I know a short freeborn would be good for this but what is the "throat"? Sorry for the format. I tried to space it out but it turned out like this.

Chamber Reamer Dimensions

Cartridge Neck F.B.L. F.B.D. Leade Throat Manufacture




6mm BR Norma . 271 .094 .2435 .2387 .3465 JGS
6mm BR Rem .271 .1163 .2435 .1001 .2302
PTG

 

[DaveTooley]

What FB bullets?

 

[afret]

Berger 68 grain FB.

 

[geo.ulrich]

the jgs is closest but .09 is still fairly long for a 68 gr. around .04-.06 would be best

 

[afret]

the jgs is closest but .09 is still fairly long for a 68 gr. around .04-.06 would be best

Thanks! These are the two choices in prefit barrels by X-Caliber. I'm planning on shooting 68 and 80 grain FB Bergers.

What if any is the relationship of freebore to the throat?

 

[geo.ulrich]

If your going between 68 and 80 gr make sure you get a 12 twist the 80s won't work in a 13-14 twist.

 

[afret]

If your going between 68 and 80 gr make sure you get a 12 twist the 80s won't work in a 13-14 twist.

Thanks for the advice. Ordered a 12 twist. Just have to wait now to have fun.

 

[Dusty Stevens]

Dont go with the br rem one. Besides the fb being too long its going to open up other cans of worms

 

[LCazador]

If your going between 68 and 80 gr make sure you get a 12 twist the 80s won't work in a 13-14 twist.

Done this! Ulrich right on!

 

[gunsandgunsmithing]

I have a .098fb 6br Norma reamer and it's been a good one. It's just about perfect for the 80s and you have plenty in the neck with the 68 bergers. Some light fb and most boat tails...not so much the case.

 

[afret]

Thanks everyone for the info and advice.

 

[Ned Ludd]

What if any is the relationship of freebore to the throat?

Technically, the term "freebore" is the same dimension as the "lead". You may sometimes hear people use the terms "freebore" and "throat" interchangeably in conversation, but that is not correct. If you look at the reamer print below, you can see that the lead dimension is 0.085" (in red), which is also the "freebore"specified by this reamer. The throat, which is in front of the lead, includes the region from the start of the land angle onward. Effectively, the freebore (or lead) is the region in front of the end of the case neck, up to the start of the rifling, but that itself has no rifling. Hence the term, freebore, or bore that is free of rifling. In fact, the freebore will often be about half a thousandth or so over bullet diameter. Hope that helps.

 

[afret]

Thank you for the explanation. It's kind of confusing since it seems like the terms are used interchangeably by different sources. I saw some diagrams where the lead is the slightly angled section beyond the freebore .

 

[Ned Ludd]

Thank you for the explanation. It's kind of confusing since it seems like the terms are used interchangeably by different sources. I saw some diagrams where the lead is the slightly angled section beyond the freebore .

I didn't want to add to your confusion, so I didn't mention the term lead angle previously. However - the lead angle is the specific angle at which the the lands rise up to their full height in the throat (i.e. right after the lead, which has no lands or grooves). This section in front of the lead where the lands begin defines the throat. On the reamer print I posted above, the lead angle is shown as 1 degree 30 (1.5 degrees), which is fairly common. Anyhow, not sure who came up with all this terminology - it was all done long before my time. But it certainly can be confusing, especially when it's not always used correctly.

 

[afret]

Thanks again. Starting to make more sense now.