Which 6BR chamber?

[kelbro]

I have a barrel about to be chambered at Shilen. There are a lot of choices for the chambering. I will be shooting Lapua brass and 105-108 bullets. I don't want to turn necks.

The choices are:

6mm Norma BR (.272)

6mm BR (.263")

6mm BR (.270")

6mm BR (.266")

6mm BR Rem


I'm guessing that the .266 and .263 require turning.

My 243AI is a .270 and I have to do very little sizing with that barrel.

.272 seems kind of big.

Which one do I need?

Thanks.

 

[areaone]

Blue box Lapua can work with .270 chamber, should be around .2675 loaded rouns, My no turn reamer from Kiff's recommendation is 2.7045. For those 105 I would want to know your FB as much as neck. FB needs to be around .100 or close to .105.

 

[Ackman]

Always get your brass first, before spec'ing the chamber. My reamer cuts a .271" neck, brass is the gold box stuff .268" loaded.

 

[DeltaBravo]

New guy here, so take what I say with a grain or two of salt!

I went with the 6BR Norma with .270 neck after talking with Dave Kiff at PTG (Shilen uses his reamers). Works like a champ! I use lapua blue box and did a skim neck turn to about 0.0135. I've fired the cases 5 times now and no signs of age or hardening; loaded neck diameter is right at 0.268. The only thing the barrel doesn't like is 87gn V-maxes! It loves Berger 80 gn Varmint FB's with 8208, H322 and BLC-2 with CCI 450's.

I went with Hodgdon's starting loads from their 2012/13 loading manual and they seem to work pretty well. Best group so far at 100 yards is 0.324 and that's after the FIRST outing using the Bergers. I expect much better results next time out.

 

[kelbro]

New, Blue Box brass from Midway. Need to give Shilen the dimensions ASAP. Won't have the brass for another week or so.

 

[Forum Boss]

I like .003 clearance on loaded rounds. This has proven accurate in many 6BR barrels, but I know others have run less clearance with success. With your blue box brass you need to check your loaded ammo with the fattest diameter bullet you will run. Some 6mm bullets will run 0.2435, others at 0.2428 and you'll find everthing in between. Kevin Thomas keeps telling us that ALL blue box brass may not necessarily load at 0.268" or less so you may be on the tight side with a 0.270 and no-turn brass. I've shot the Blue box in a 0.272 neck chamber and it was fine. Right now I like a 0.271 for the Blue box. YMMV.

 

[DeltaBravo]

New, Blue Box brass from Midway. Need to give Shilen the dimensions ASAP. Won't have the brass for another week or so.

I drove Shilen crazy (sorry Sherry and J) with phone calls and e-mails before I decided on the .270 neck. Just mention my name and they'll "take care of you." They are GREAT folks and very tolerant! I would go with the .270 neck just because you can start with the blue box and do nothing other than shoot it; you can always neck turn it if you're not comfortable with .002 clearance. I'm just starting out, so minding the Forum Boss's recommendations are probably in order!

When my DGV action was ready, Dave at Shilen showed me how to put it together (I went with the barrel nut version) and set it up. Shilen is great!

 

[fdshuster]

kelbro: I'd also suggest the .270" neck. I had my .272" necked reamers (great with the old gold box Lapua) re-ground to .269" for the "new" blue box and that works fine for the loaded round (105 Bergers) neck diameter of .2675". I can load them as-is or do a light cleanup outside neck turn.

One of my reamers has the traditional .104" freebore & it works fine with the 105 Bergers, 107 SMK & 108 Bergers, but the bullet full .243" dia. is almost half way up the case neck when seated to touch. At around 1000 rounds fired, they are getting close to the case mouth. Having a new reamer cut now, this one with .050" FB, that will still put the bullet base in front of the donut, but deeper in the case neck. The 105 Bergers & 107 SMK will clear the donut, the 108's will not, so I'll not use the 108's until enough erosion develops.

Those long, heavy bullets will lengthen the throat, and at around 1000 rounds fired, it will get your attention when wanting to seat to touch the lands. They will have "moved" forward a significant distance.

 

[kelbro]

Thanks. I'm on the fence between having a known good barrel re-chambered at Shilen and buying a new McGowen from Jim at Northland. He says the McGowen has a .272 neck throated for the 100 gr + bullets.

 

[Sled2live]

Pardon my ignorance, I am new to the 6BR cartridge, and to this forum. I have been reading everything I can find for the last month or so and the original post just confirmed my ignorance. Can someone tell me the difference between the OP's choices:

6mm Norma BR (.272)

6mm BR (.263")

6mm BR (.270")

6mm BR (.266")

6mm BR Rem

Do I actually see 3 different rounds? I thought that the 6mm Norma BR was the basic round that was settled on to be known as the 6mm BR.???
I thought the 6mm BR Rem had a different neck length thus a different overall length.

I am a confused newbie. Sorry for the interuption of this thread....but I figured you folks are the best to get my answers from.

Thanks
Scott

 

[fdshuster]

Scott: Yes, 2 different chamber dimensions. The 6BR Norma, same as 6BR Lapua, (brass is interchangable), and the original 6BR Remington, shorter chamber length and smaller case head diameter. The Remington brass would fit in the Norma/Lapua chambers, but not the reverse.

 

[hogpatrol]

Probably goes without saying but remember you can always go bigger on the chamber neck.

 

[expiper]

and,,,as reply # 1 said ...the FB is just as important,,,,I like it ~.080" in my 6mmBR's,and .271" ND ...(the Dashers/BRX/etc have shorter neck and require deeper longer FB ((.100-.140)) to achieve the same donut clearance) ....this is another reason to have your own reamer from Kiff and not rely on the gunsmith using whatever he has layin around ,,sometimes from early days aka Rem BR!!,,,and then you get a chamber that is not current or correct for the twist/bullets that you plan on using...Shilen should be ready and willing to send/fax/e-mail you reamer drawings showing exactlly wht they have and are going to use on your bbl...dont let anyone rush you into the wrong thing...Roger

 

[Killshot]

Thanks. I'm on the fence between having a known good barrel re-chambered at Shilen and buying a new McGowen from Jim at Northland. He says the McGowen has a .272 neck throated for the 100 gr + bullets.

Kelbro, If they can do one with a .270" neck, that is the one that suits the current "Blue Box" Lapua brass loaded with a Berger 105gr Hybrid.
FWIW Kiff's "World Record Dasher" reamer has a .2704" neck and a .104" Freebore, it works very, very well.

 

[Steve Blair]

My 6BR reamer is Ø.269" for turned necks with either gold or blue box. Like Paul, I find .003" diametral clearance works very well. My freebore is .104" but could be a little shorter if you wanted to shoot some lighter varmint bullets. The 6BR has a long neck and is pretty tolerant on seating depth.

 

[Bradley Walker]

They want to cut my new barrel with the "new" PTG reamer that has the .2704" neck.

My brass is all gold box.

Is that OK?

Holy crap I hate this whole gold box blue box crap.