Neck O.D.

Tom Berridge

Tom Berridge

New member
I need help, loaded some new rounds for my 6BR and after checking found out the loaded neck O.D. with bullet is .269
The chamber neck is .270, what is the opinion on firing these rounds safely with only .001 clearence.
The brass is new Lapua with neck thickness of .013 ,yes I should have turned the necks !
Thanks...Tom
 
Tom Berridge said:
I need help, loaded some new rounds for my 6BR and after checking found out the loaded neck O.D. with bullet is .269
The chamber neck is .270, what is the opinion on firing these rounds safely with only .001 clearence.
The brass is new Lapua with neck thickness of .013 ,yes I should have turned the necks !
Thanks...Tom
Click to expand...

First of all let's be clear on one thing...... clearance is clearance.



period.



.001

or

.0001

or

.004


it just doesn't matter as far as safety goes.....

I shoot some of my cases with .0000 clearance or even a tiny interference which makes visible marks on the casenecks....(the #2 shooter in the IBS HOF calls this "scuff fit" ;) ) .... with no issues. Clearance CANNOT change the pressure curve materially in and of itself, there's no mechanism for it. Obviously if you're feeling resistance of any sort this whole discussion becomes moot, it doesn't take a whole lot of force to turn "minimal clearance" into "crimped onto the bullet" but YOU WILL FEEL IT. And, not so obviously, clearances under .001 can be used for pressure curve tuning, especially with boattails as they seem to obturate up differently than FB bullets (my opinion ONLY)

I've done it. Mistakenly and on purpose. Many times. Up to and including lightly crimping....... I've never found danger until one is forcing the bolt closed. In other words, if it closes normally, easily, there's no danger of pressure spiking. And if one is forcing ANYTHING one had best know exactly where the interference is!

That said, some especially in the short-range group games feel that a little more clearance is beneficial to accuracy ("thin to win")

but IMO your question concerned safety.

IME you are safe as long as the cases go in easily.

al
 
I just took a new 6BR case and seated a 105 Berger Tail bullet, which measures .2428. The neck measures a few tenths under .271.

How did you arrive at .269 in a unturned case.
 
jackie schmidt said:
I just took a new 6BR case and seated a 105 Berger Tail bullet, which measures .2428. The neck measures a few tenths under .271.

How did you arrive at .269 in a unturned case.
Click to expand...

Jackie,the neck thickness with tube mike is .013 on one side, .013
.013
.243
--------
.269
Am I thinking right ?
Thanks, Tom
 
jackie schmidt said:
Did you actually mic the loaded round?
Click to expand...

It fascinates me how we all think differently.... :)

I have dozens of measuring devices, mics of all sorts with rods and anvils, blades, hooks and offsets for measuring everything under the sun BUT I NEVER MEASURE ANYTHING to arrive at a number!!

To me measuring and adding numbers is "last resort" stuff, just multiplying my propensities for error. I GAUGE whenever possible and measure OVER THE STACK when measuring. In other words, if I want to SWAG at my "neck thickness" I'll measure up 6-8 loaded rounds all over the neck, measure 6-8 bullets from the same lot and subtract the two numbers......divide by two.

And consider that "close."

In the end FEEL is the final arbiter....and how they hold a bullet, how they size. Modern technology has produced a surreal sense of sameness with reamers and bushes and dies and such....., I've come to actually EXPECT neck bushings to be right! But stuff still has to be mfgd to tolerance.

Plus, it wasn't until I started doing my own chambers that I EVER got stated neck diameter dimensions...I bought 4 6BR reamers while I had others doing my chambering. I started with the recommended .274, almost immediately bought a .272....then a .270 and a .269... and never even got an interference until I did some of my own with the .269.

I'm not complaining, just stating facts. All of these reamers are useful. and most of these chamberings (.269/.270 even the .272 sometimes) will "hold a bullet" after firing such that I can reload using only a decapping pin and primer seater and the tight ones are so tight you can't seat the new bullets with your fingers......you need a Wilson die.

And "good" cases, cases which have been fondled into submission always seem to iron out to just a little thinner than new. It takes several firings just to get the wrinkles out, get them ready to turn for final fit in a tight-neck

but I ramble


al


out
 
Don't add the individual measurements together to get the neck dimension.

Measure the neck with a bullet seated (over the base of the bullet if it's a flat base). -Al
 
alinwa said:
First of all let's be clear on one thing...... clearance is clearance.



period.



.001

or

.0001

or

.004


it just doesn't matter as far as safety goes.....

I shoot some of my cases with .0000 clearance or even a tiny interference which makes visible marks on the casenecks....(the #2 shooter in the IBS HOF calls this "scuff fit" ;) ) .... with no issues. Clearance CANNOT change the pressure curve materially in and of itself, there's no mechanism for it. Obviously if you're feeling resistance of any sort this whole discussion becomes moot, it doesn't take a whole lot of force to turn "minimal clearance" into "crimped onto the bullet" but YOU WILL FEEL IT. And, not so obviously, clearances under .001 can be used for pressure curve tuning, especially with boattails as they seem to obturate up differently than FB bullets (my opinion ONLY)

I've done it. Mistakenly and on purpose. Many times. Up to and including lightly crimping....... I've never found danger until one is forcing the bolt closed. In other words, if it closes normally, easily, there's no danger of pressure spiking. And if one is forcing ANYTHING one had best know exactly where the interference is!

That said, some especially in the short-range group games feel that a little more clearance is beneficial to accuracy ("thin to win")

but IMO your question concerned safety.

IME you are safe as long as the cases go in easily.

al
Click to expand...
Thanks to all for the help,to those how asked,yes I did measure the loaded rounds with a caliper and it measured .269
I felt no resistence closing the bolt and shot two five shot groups today and was suprised at the two groups, a .162 and .184
Thanks again,Tom
 
Tom Berridge said:
I need help, loaded some new rounds for my 6BR and after checking found out the loaded neck O.D. with bullet is .269
The chamber neck is .270, what is the opinion on firing these rounds safely with only .001 clearence.
The brass is new Lapua with neck thickness of .013 ,yes I should have turned the necks !
Thanks...Tom
Click to expand...

It is "safe", but...

I set up my 6mmBR with 9 thou neck walls... 1 thou total clearance, (actually, 0.00075"). It would shoot well, but was a real Prom Queen to live with - I needed to scrub the barrel every time I looked at it - it was fussy, so much so, that it wound up collecting dust, waiting for time to redo something.

Then I watched a series of videos made by Jack Neary...

https://www.youtube.com/watch?v=7SZWvn68bRU&list=PL7D85822FD9E41FF2

... and Jack talked about how he was shooting a 1 thou neck and he talked about having the same problems as I was.

... so I re-cut my necks to 0.0083", and instantly, the rifle became a joy to shoot and live with.

Watch the video series - it is some of the best advice you can get.
 
Last edited:
As alinwa said, any clearance is enough to shoot safely but the smaller the clearance the more often you have to check your loads. I'd turn those necks a bit more if it were me.
 
jackie schmidt said:
Did you actually mic the loaded round?
Click to expand...

Yes Jackie I did measure the loaded rounds at the bulllet pressure ring and it was .269
I fired these rounds on Friday and everthing went well,and the groups were very good.
There was no resistance in chambering or extraction.
But I think I will turn those cases too .012 for future loading.
Thanks Jackie
 
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