Seating depth for 6br heavy bullets

[Hatrick]

I am new to the 6br, and just had a 700 re barreled with a broughten 8 twist that was chambered with a PTG .270 nk reamer.

In preparing to load some 107 smk's I found that to touch the lands they are seated at 2.375" which only leaves the bullet shank about .225" in the neck, not counting the boat tail of course. I loaded some dummy rounds just to be sure that I was not mistaken in measuring, they chamber with no problem, and show very slight contact with the lands.

Does that seem normal for what I have or is there excessive free bore for some reason?

TIA for any help. ;D

 

[deadlyswift]

I messured your .225 on a 6br case. Looks like you are good to go! Now just charge those dummy rounds and enjoy slinging some lead down range. I'd say you are in a good spot. Plenty of room to jump the SMKs, and stay away from the dougnut in the shoulder/neck junction.
Thanks
Mark

 

[NorCalMikie]

That's the difference between getting a barrel chambered the way "you" want it and getting it chambered by what someone else says. Dummy round set with the longest bullet you plan to shoot, set real close or jammed into the lands and bullets set close to the shoulder neck junction.
I prefer as much bullet in the neck as I can get. The throat can only get longer as more rounds are fired.
On your "next barrel", get a shorter throat.
Shoot this one till you run out of neck. ;D
You may be surprised just how accurate it will be the way it is now.

 

[in2deep]

My 6BR hates the SMK's jammed (8 inch groups at 300 yds.) but back them out to .100 jump and it can touch holes at 300 yards. My problem is the bullets seem to be too far into the case and actually touch the powder but it shoots bug holes so you never know what works till you try it.
The Berger method of seating bullets at various jumps out to .100 helped me develop a load after struggling with loading too close to the lands. JLK's and lapuas all like to jump in my barrel too.

 

[mbkmkk]

Hatrick

Sorry for a off topic question but,

What caliber was the 700 before you re-chambered it? I am looking to do the same thing and want to be able to use the magazine.

Thanks

 

[Hatrick]

Hatrick

Sorry for a off topic question but,

What caliber was the 700 before you re-chambered it? I am looking to do the same thing and want to be able to use the magazine.

Thanks

308 win. I have only fired 20 rounds breaking in the new br barrel, but I did try a few feeding from the mag, and if I loaded them as far forward as they will go they fed okay. There are mods that one can do to enhance reliable feeding. I had to remove the ejector because it was causing case mouth deformation, so right now it is a single action. I may clip a couple coils from the spring and see if the ejector is any more gentle on the case necks.

 

[hogpatrol]

in2deep, Did you mean to say ten thousandths of an inch instead of a hundred thousandths of an inch jump? Just wondering. Thanks.

 

[in2deep]

This taken from a Berger article below and yes I believe I am saying it correctly the comparator shows the jump as .100 off the lands and it shot so good there i never tried .120:

Load 24 rounds at the following COAL if you are a target competition shooter who does not worry about jamming a bullet:
1. .010 into (touching) the lands (jam) 6 rounds
2. .040 off the lands (jump) 6 rounds
3. .080 off the lands (jump) 6 rounds
4. .120 off the lands (jump) 6 rounds

At first I was hesitant since it seemed an excessive amount and I feared blowing something up but the nice fellow that makes JLK bullets suggested I try it and he was right.

 

[Steve Blair]

I am new to the 6br, and just had a 700 re barreled with a broughten 8 twist that was chambered with a PTG .270 nk reamer.

In preparing to load some 107 smk's I found that to touch the lands they are seated at 2.375" which only leaves the bullet shank about .225" in the neck, not counting the boat tail of course. I loaded some dummy rounds just to be sure that I was not mistaken in measuring, they chamber with no problem, and show very slight contact with the lands.

Does that seem normal for what I have or is there excessive free bore for some reason?

TIA for any help. ;D

Your numbers sound like a .080" freebore reamer was used. My 6BR reamer is a .104 freebore and seats Sierra 107s at 2.400", just touching. By my reckoning, your freebore is a little short for long bullets. It really depends upon what your application is. If you are feeding from a magazine, it is reasonable to have a fair engagement depth. If your rifle is single shot, engagement can be quite short and still function well. Seating out a little farther provides some more powder space and can reduce or eliminate compressed loads.

 

[Hatrick]

I am new to the 6br, and just had a 700 re barreled with a broughten 8 twist that was chambered with a PTG .270 nk reamer.

In preparing to load some 107 smk's I found that to touch the lands they are seated at 2.375" which only leaves the bullet shank about .225" in the neck, not counting the boat tail of course. I loaded some dummy rounds just to be sure that I was not mistaken in measuring, they chamber with no problem, and show very slight contact with the lands.

Does that seem normal for what I have or is there excessive free bore for some reason?

TIA for any help. ;D

Your numbers sound like a .080" freebore reamer was used. My 6BR reamer is a .104 freebore and seats Sierra 107s at 2.400", just touching. By my reckoning, your freebore is a little short for long bullets. It really depends upon what your application is. If you are feeding from a magazine, it is reasonable to have a fair engagement depth. If your rifle is single shot, engagement can be quite short and still function well. Seating out a little farther provides some more powder space and can reduce or eliminate compressed loads.

It was chambered with a PTG Lapua blue box reamer, here is the print if this link works.

http://www.accurateshooter.com/forum/index.php?action=dlattach;topic=3763318.0;attach=872507

 

[Steve Blair]

The print shows a .101" freebore, pretty common for long bullets. It is a little surprising that your bullets do not seat longer but there are a number of variables at play. It is otherwise a standard no-turn chamber for current Lapua brass. You should be good to go. Be sure to check your loaded neck diameter. If it is over .268", I would consider a light turn. If they are at .268" or under, shoot and enjoy.

 

[Hatrick]

The print shows a .101" freebore, pretty common for long bullets. It is a little surprising that your bullets do not seat longer but there are a number of variables at play. It is otherwise a standard no-turn chamber for current Lapua brass. You should be good to go. Be sure to check your loaded neck diameter. If it is over .268", I would consider a light turn. If they are at .268" or under, shoot and enjoy.

Yes the loaded case necks measure a hair under .268, so I will not bother turning. After firing, the necks are left at .269 and I have bushings at .266 and .267 to try for resizing.

 

[BoydAllen]

I lack long bullet/range experience, but I know that some very good short rang shooters find that .002 - .003 neck clearance on a loaded round gives them superior results at 200 than less clearance. I think that it is about clearance for bullet release. I have also heard that one successful .30 cal. 1,000 yd. shooter has found that he gets better results with as much as .005 clearance. Evidently, sometimes closer isn't better.

 

[Steve Blair]

My experience is that the larger the caliber, the more clearance needed. Perhaps it is a percentage relationship. My 6BR does very well with a .269 chamber and .2665 loaded diameter. My .284 is .313 chamber and .309 loaded diameter. The .308 chambers are .342 and .343 versus loaded diameters of .338.