Help me spec a 6BR reamer

[Patruck825]

Morning guys,

I'm planning on spec'ing a reamer with JGS or PTG to send to my smith to have it on hand to make barrels for me.

The current 6BR reamer they have has a .271 neck and id like at least a .272 or .273 neck. My Current barrel is a little tight with lapua blue box.

I plan on continuing to shoot 105 hybrids, what freebore should i request? Neck? Freebore Diameter?

My loaded rounds measure .2695, and the 105 hybrids typically measure .2434-.2436 at the p ring

I dont know much about reamers or what aspects are important to specify so any guidance would be appreciated.

 

[powderbrake]

If you email or call JGS, they will send you a print of a 6BR reamer. If you don't like the neck diameter, ask for a print with the neck diameter that you desire. Also, you need to spec the freebore for the bullets that you plan on using. I did a search here a while back for this info, and there were a range of freebores, and they ranged from .094 to .104 for the Berger 105 Hybrids.

I recently ordered one from JGS which has a .272 neck and a .102 freebore to shoot both the 88 and 105 Bergers. I have not received it yet, so I cannot comment on it. I also had a slightly tight neck, and wanted to go to .272 for no-turn cases. My current barrel has a longer freebore, simply because it has so many rounds fired.

Neck diameter and freebore are two items that many shooters have preferences for, and there are a range of opinions on the proper choices.

Here is a link to a thread on this subject
http://forum.accurateshooter.com/threads/6mm-br-no-turn-reamer-suggestions.3936689/

 

[Patruck825]

This is my current reamer, correct me if I’m not reading this correctly but does this show my FB at .107?

 

[hrlincoln]

This is my current reamer, correct me if I’m not reading this correctly but does this show my FB at .107?

View attachment 1062257

Letter box 'U & V'...your freebore is .0940

 

[expiper]

Morning guys,

I'm planning on spec'ing a reamer with JGS or PTG to send to my smith to have it on hand to make barrels for me.

The current 6BR reamer they have has a .271 neck and id like at least a .272 neck. My Current barrel is a little tight with lapua blue box.

I plan on continuing to shoot 105 hybrids, what freebore should i request?

I dont know much about reamers or what aspects are important to specify so any guidance would be appreciated.

CALL DAVE KIFF,,,he will walk you thru it,,,,Roger

 

[BRGUY]

Since you are looking at a new reamer, get one with "0" free bore and allow your gunsmith to cut the throat separately, so you can get exactly the free bore length you want. This will allow your gunsmith to be able to cut many more chambers with this particular reamer, and then he can cut any throat length that other customers may desire.

 

[Patruck825]

What FL die are you using, as most are set up to size the base correctly with SAMMI dimensions on letter box "B" .4714" Dave has helped lots of folks but also has caused the need multiple times for custom dies because he reduces this diameter. I have seen older reamers on here for sale that go all the way to .470" at the .200" line, if you heard the term "clickers" this is when the bolt has to be forced open at the very top of lift due to case/chamber not having enough clearance. The print above 1262 is a great reamer, and have owned that tool. Jim O`Hara spoke of opening up the freebore diameter and it made a positive difference immediately, so I followed his lead and all my reamers now get the .2438" letter box "G" and "I" the .100" freebore will work, but to help case capacity, I still prefer a .140" freebore, letter box "U" and "V". I also agree with your assessment needing a larger neck diameter as I feel .004" is the proper clearance here.

Dang, I might order this reamer myself....Lol!

Currently i am using a Harrells die they gave me from some fired brass i sent them. My fired brass measured out to .4705 at the .200 line, which doesnt exactly jive with what the the reamer says.

My loaded rounds measure out to .2695, so id be looking at a .273 - .274 neck. I had some pressure issues early on and i think it had to do with the neck, a bullet doesnt drop freely (only barely) into a fired case. Hard to complain though as the thing is very accurate.

.2438 at the G and I box sounds like a good idea as well, as my 105's typically measure out to .2435-.2436

 

[Patruck825]

Question for you guys, can you use this reamer print to determine your Base to Ogive length? Looking at the reamer print, none of the measurements i would think to use seem to line up with the measurements ive pulled using the stoney point gauge, i get a BTO length of 1.7930

 

[#40Fan]

Question for you guys, can you use this reamer print to determine your Base to Ogive length? Looking at the reamer print, none of the measurements i would think to use seem to line up with the measurements ive pulled using the stoney point gauge, i get a BTO length of 1.7930

That is because the tool isn't touching the same spot on the bullet that the rifling will.

 

[Patruck825]

That is because the tool isn't touching the same spot on the bullet that the rifling will.

Which makes perfect sense, i just thought it would be closer.

 

[JFrank]

This is my current reamer, correct me if I’m not reading this correctly but does this show my FB at .107?

View attachment 1062257

Yes. .094 freebore
Nothing wrong with.271 neck just clean up turn and your good to go
I would consider a.104 freebore on an 8 twist to keep your Bullets ahead of any potential doughnuts

 

[Patruck825]

Yes. .094 freebore
Nothing wrong with.271 neck just clean up turn and your good to go
I would consider a.104 freebore on an 8 twist to keep your Bullets ahead of any potential doughnuts

Im not looking to neck turn, this is no benchrest gun and i am okay with lapua brass as is.
Im currently shooting a 7.5 twist and plan to stick with that for the stability of the 105s in all conditions.
.104 freebore sounds close to where i want to be

 

[Patruck825]

Ive seen Freebore recommendations of .104, .114, .120, and .140. Whats the advantage of going with one over the other? .140 seems really long if you were to end up chasing the lands. I usually shoot my bullets with a .015 jump

 

[Patruck825]

Get out your calipers and see just how long that is. Open them to .036" thousands and see the difference.

I know its not much, but why all the preferences then? Are there any studies on optimal freebore for a particular bullet?

 

[Patruck825]

I want the bearing surface of the bullet above/into the sized portion of the neck. If seating and the bearing surface has to go further in past the sized area you`ll loose neck tension. It will result in inconsistent vertical at distance.

105 Hybrids and 108 Bergers have the longest bearing surface.

Your last post said it seemed really long, go get your calipers and see.

So is there a hard number for freebore where that bearing surface stays above the doughnut with a 105 hybrid?

 

[Patruck825]

Donut???? OK new territory. .040" should work!

I assumed that was why you wanted to stay above the unsized portion of the brass, if not, just ignore it. I obviously don't know a ton about this and am looking to learn.

 

[Patruck825]

I didn`t type un-sized.

If you want the bearing surface to stay in the sized portion of the neck, then that is the same as keeping it out of the unsized portion of the neck. It seems you're just enjoying picking things apart rather than helping.

 

[tclaunch]

I assumed that was why you wanted to stay above the unsized portion of the brass, if not, just ignore it. I obviously don't know a ton about this and am looking to learn.

I will bow out.

 

[Patruck825]

I will bow out.

If that is easier than being productive, please do.

 

[tclaunch]

I have helped so many people you would not believe. All advise was helpful. I just hardly ever try here for obvious reasons. Good luck in your quest.