6mm BR newby neck dimension question.

[Just Say Moe]

My chamber is for 0.272 neck.
My resized, barely turned brass (0.012 thick) is 0.262 (standard FL dies)
My loaded ammo is 0.264
My fired brass is 0.269

From what I have been reading here, I'm thinking I need bushing dies, but what bushing? 0.266 or 0.267?
thanks!

Edit - turned brass is 0.012 not 0.0012

 

[rockrat]

Don't have much experience with bushings, but I would think 0.262". Thinking springback of the brass to maybe 0.2625 which would leave 0.0015 neck tension if your loaded ammo is 0.264". That being said, you seem to have 0.002" neck tension now, so do you really need bushing dies?

Those a lot smarter than I should chime in shortly.

 

[RegionRat]

Something is a little off on the numbers if his neck thickness is indeed 0.012" and not 0.0012"?

Let's say the bullet OD is .243 and the brass is 0.012"
(2 x 0.012") + 0.243" = 0.267" OD (over the loaded round.) (Not sure how OP gets to 0.264, unless he turned farther than we think and that brass is below 12 mils? Maybe we should double check a loaded round OD and the thickness again?)

That implies he wants to size down about 2 mils for a bushing dia of 0.265" so he should have bushings from 0.264 - 0.266 and be ready for as many steps in between as he can source.

Having a spread of bushings and expander mandrels means you are ready for brass changes as time goes on.

 

[HTSmith]

Generally I start with a bushing .002" smaller than a loaded round, but I'll also test .001 and .003 smaller. That said you are turning way more brass than you need to for a .272 neck. A loaded round neck diameter of .268 would likely give you a good cleanup, be less work, and help your brass last longer.

 

[Texas10]

I have a selection of bushings for my 6br, so I'd suggest you get .263, .262, .261 bushings. Whether you load in or off the lands, neck tension will play a key role and a bit of experimentation will help you decide what size bushing works best with your seating depth, and how often you will need to anneal.

 

[J.J. Coe]

My chamber is for 0.272 neck.
My resized, barely turned brass (0.0012 thick) is 0.262 (standard FL dies)
My loaded ammo is 0.264
My fired brass is 0.269

From what I have been reading here, I'm thinking I need bushing dies, but what bushing? 0.266 or 0.267?
thanks!

First thing I would do is check your measuring equipment. If you're actually turning the necks to .012 your loaded round dimension should be .267-.2675ish.

 

[Eric Leonard]

With a .272 neck chamber I would try shooting the rifle with some brass right out of the box with a .267 bushing which will be real close to a .269 loaded round and come out after fires at .2715 or so.

I haven’t been able to tell any difference on target from turned or unturned brass in a .272 no turn chamber

 

[Ccrider]

With a .272 neck chamber I would try shooting the rifle with some brass right out of the box with a .267 bushing which will be real close to a .269 loaded round and come out after fires at .2715 or so.

I haven’t been able to tell any difference on target from turned or unturned brass in a .272 no turn chamber

.0005 clearance is hard to hold. If the factory brass and your bullets are perfect you may be ok. Also watch for any build up in your necks if you do this. I would clean the necks up at a minimum. I would want at least .2705 and would be fine with .270 in a .272 chamber.

 

[jackieschmidt]

By 6BR reamer has a .269 neck.,I turn my necks to .012 thick, and the newer brass barely cleans up to that. I use a .265 or .266 bushing.

Your 272 neck just might work fine with a no neck turn Case. .273 would be ideal. If you have turned your necks to .012, then a .266 should work fine. You will simply get a little more neck expansion than I do with my .269.

 

[Eric Leonard]

.0005 clearance is hard to hold. If the factory brass and your bullets are perfect you may be ok. Also watch for any build up in your necks if you do this. I would clean the necks up at a minimum. I would want at least .2705 and would be fine with .270 in a .272 chamber.

The .2715 is what the necks measure after being fired before sizing. Loaded rounds before firing are .269

 

[Just Say Moe]

Thanks for the replies. Yes, the neck thickness is 0.012. In my next batch of brass, I will not turn them any in order to get the loaded diameter closer to the 272 neck.

I was thinking not sizing the brass down so much would aid in getting closer to 269 loaded rounds. Am I going up the wrong tree here?

 

[RGRobinett]

When you get into neck-turning, measuring with a caliper (+/- 0.001") won't cut it - you need to have/use a micrometer capable of resolving 0.0001s of an inch (+/- 0.0001"). RG

 

[Just Say Moe]

When you get into neck-turning, measuring with a caliper (+/- 0.001") won't cut it - you need to have/use a micrometer capable of resolving 0.0001s of an inch (+/- 0,0001"). RGThanks - I forgot I have one - it looks like 0.0117 thickness.

Thanks - I forgot I had one - it looks like they are about 0.0117

 

[Delfuego]

but what bushing? 0.266 or 0.267?

I would get a .266, .267, .268 One of these will work.
You could have your dies honed to the neck you want too.
Even easier would be to get a Harrell's die to match your chamber. It will have the correct neck and correct base.

 

[Ccrider]

The .2715 is what the necks measure after being fired before sizing. Loaded rounds before firing are .269

Ok. I misread and was thinking .2715 finished round. .269 loaded round would be fine. After firing a bullet should drop into the neck.

 

[Texas10]

Reading is definitely a perishable skill. I find I cross check myself all the time.

OP states loaded round measures .264?

.263 would be the largest bushing to use and would probably give less than .001 neck tension when accounting for spring back, which may work best if seating lightly into lands. But something doesn't add up.

So I measured my no turn neck .272 6br and get a .269 loaded round with Lapua brass. Shot dia is .2712 and sized using a .268 bushing is .2688 making for very light neck tension while seating .010 into lands.

 

[Eric Leonard]

Reading is definitely a perishable skill. I find I cross check myself all the time.

OP states loaded round measures .264

.263 would be the largest bushing to use and would probably give less than .001 neck tension when accounting for spring back, which may work best if seating lightly into lands.

For measuring neck wall thickness accurately a tube micrometer is minimum acceptable equipment.

Or maybe I need to start taking memory enhancement meds!

I suck at measuring any tube wall thickness. When I turn necks all I go by is what the loaded round measures with the bullet I’m gonna shoot seated

 

[tmwinds]

With a .272 neck chamber I would try shooting the rifle with some brass right out of the box with a .267 bushing which will be real close to a .269 loaded round and come out after fires at .2715 or so.

I haven’t been able to tell any difference on target from turned or unturned brass in a .272 no turn chamber

^^^This. There is a reason a .272 chamber neck is called a No Turn neck.

 

[Lefty Trigger]

The OP did not mention who's brass he's using either, it does make a difference. I load both Norma and Lapua and to get proper neck tension for the same bullet I needed two different size bushings. To keep from getting confused or forgetting to change bushings I set up two complete sets of dies and labeled them "Lapua" and "Norma"

 

[dolek]

The OP did not mention who's brass he's using either, it does make a difference. I load both Norma and Lapua and to get proper neck tension for the same bullet I needed two different size bushings. To keep from getting confused or forgetting to change bushings I set up two complete sets of dies and labeled them "Lapua" and "Norma"

Good point right there, the difference between gold box and blue box Lapua may even need a different bushing for same neck tension .