Re-chamber 6BR to 6mmAI?

[Hotshot]

Has anyone attempted or accomplished this re-chamber? A respected gunsmith told me a re-chamber to 6mm would require a set back of .400. He couldn't answer for sure on the 6mmAI. Said he would need a chamber cast and the dimensions of the reamer because it was really close. I can't find the dimensions
for the 6mmAI anywhere on the net and I thought maybe someone here has worked on a project like this. I know I could go 6-284, 243AI, even 243wssm if I wanted to change bolt face. However I have 6mmAI comp dies, several hundred brass and a history with the cartridge so I'm set on the 6mmAI.
The problem with set back on my Shilen 6BR barrel is the barrel begins to taper immediately after the threads(Savage small shank) so if I set back very far there is no room to cut more threads. Please help if you have experience. And please tell me where to find dimensions for the 6mmAI cartridge if you know where I can get them.

 

[CatShooter]

Has anyone attempted or accomplished this re-chamber? A respected gunsmith told me a re-chamber to 6mm would require a set back of .400. He couldn't answer for sure on the 6mmAI. Said he would need a chamber cast and the dimensions of the reamer because it was really close. I can't find the dimensions
for the 6mmAI anywhere on the net and I thought maybe someone here has worked on a project like this. I know I could go 6-284, 243AI, even 243wssm if I wanted to change bolt face. However I have 6mmAI comp dies, several hundred brass and a history with the cartridge so I'm set on the 6mmAI.
The problem with set back on my Shilen 6BR barrel is the barrel begins to taper immediately after the threads(Savage small shank) so if I set back very far there is no room to cut more threads. Please help if you have experience. And please tell me where to find dimensions for the 6mmAI cartridge if you know where I can get them.

Re-chambering to the 6mm Rem will need the setback because the shoulders of the 6mm Rem are smaller than the shoulder of the 6mmBR.

If you chamber for the 6mm Remington AI, the new chamber will completely clean up the old chamber, and you won't need to set the barrel back.

 

[MarkS]

The 6BR chamber is bigger than the 6AI or 243AI. You will need to cut the 6 br chamber off to start, then chamber

Mark Schronce

 

[CatShooter]

The 6BR chamber is bigger than the 6AI or 243AI. You will need to cut the 6 br chamber off to start, then chamber

Mark Schronce

My chamber diagrams show the shoulder of the 6mmBR is 0.460" - and the shoulder of the 6mm Rem AI is 0.468"... The 6mm Rem AI should completely clean out the 6mmBR.


The 243 AI will not clean up the old chamber - sorry, it is not a favorite of mine.

 

[Hotshot]

Thanks CS and Mark. I am going to make a chamber cast of the existing chamber, then compare to my reamer. I will report here what I find in case anybody else faces this problem.

 

[jonbearman]

This is a dumb question,but why abandon a superior cartridge such as the 6 br in lieu of the 6mm rem. What contour is your barrel. I might be willing to trade you a 6 rem shilen for the 6 br. Mine is a 26" heavy b arrel much like a remington varmint contour.

 

[1000yardstare]

Measured my 6AI cases and they are .457 at the shoulder. The Sierra manual says .455.

Bill

 

[expiper]

Dear Hot....over the years I have re-chambered several BR's to .243 win and there has been a little teeneee weenie line around the chambers where the BR body ended and the shoulder began .....but....they shot well and the ctgs resized well in the resize die....I didnt loose prescious bbl length or gun wt. ...the gunsmiths wana cut and nip and tuk at every opportuntiy.....the one that I am currently shooting had 1300 rds as a BR and now an additional 1900 as .243 win.....it is a Krieger LV--8 twist --28.5" long....and still shooting .2's .3's at 100yds with 105 +/- everythings ....it you dont let it bother you the liddle ring around the ctg. case body wont bother the gun !!!!...Roger

 

[Hotshot]

After much thought and study, it was still real close as to whether this would work or not. I printed many blueprints of the two cartridges with no two having exactly the same dimensions. The advice I received was mixed. Finally I just told Bob to cut it!
The chamber came out great. Mirror smooth all the way, I can't wait to do some load testing to see how it shoots. A little issue called fire forming must come first.
Will it work for you? I can't say that it will for sure. Will I do it again? I'm already shopping for another good 6mm BR Norma 1:8 twist barrel.
Thank you all for your input.
Mark

 

[C. Collins]

This is a dumb question,but why abandon a superior cartridge such as the 6 br in lieu of the 6mm rem. What contour is your barrel. I might be willing to trade you a 6 rem shilen for the 6 br. Mine is a 26" heavy b arrel much like a remington varmint contour.

I am not trying to start a pissing match, but at this time I prefer a 6 rem to a 6 br. At 600 yards the BR does not shoot as well as the 6 rem. Its just my experience.

 

[Hotshot]

Chef,
I think you are really deep down a trouble maker! Please leave me out of this argument.
My purpose was to shoot long range varmints, for which I prefer the flatter trajectory of a larger capacity cartridge. Less figuring and fewer clicks.
Now, please go back to poking the Grizzly with sharp stick.

 

[rbertalotto]

Good for you Hotshot! It's always fun to experiment.

I'm a huge fan of the 6mm cartridge, both standard and Ackley. I shot many years in competition with various rifles and barrels in the 6mm AI. A much better cartridge ImO than the 6-284 for long range shooting.

But then I started shooting the 6BR and I just couldn't justify the extra powder and extra wear and tear on the barrels throat for such a little gain in velocity and zero improvement in accuracy. In fact, every 6BR I've ever built has ALWAYS outshot any of my various 6mm rifles.

But then I wanted to shoot 100+ grain 6mm bullets so I returned to the 6MM Ackley. Success was OK, but I missed the inherent accuracy and very easy to reload 6BR.

And then God smiled on us all and the 6.5-47 Lapua cartridge became available. Necked down to 6mm it will do everything a 6mm will do but with less powder and some of the best factory brass I've ever laid hands on. Accuracy like a 6BR, very kind to the barrels throat, excellent available brass and accuracy like 6BR/6PPC..........

Sorry, had nothing better to do this AM so figured I'd throw this out there!