Neck clearance question

E

ehkempf

Guest
I have three 6MM BR’s all with .272 neck. The old Lapua would give me a loaded round size of .269. The newer Lapua is now at .267, Remington 6MM BR brass also measures .267. I don’t have any Norma brass so I don’t know what size it is. Is there a point where there is too much clearance and that accuracy will be affected? What is too much clearance, and what is optimal?


Thanks,

Ed
 
ehkempf said:
I have three 6MM BR’s all with .272 neck. The old Lapua would give me a loaded round size of .269. The newer Lapua is now at .267, Remington 6MM BR brass also measures .267. I don’t have any Norma brass so I don’t know what size it is. Is there a point where there is too much clearance and that accuracy will be affected? What is too much clearance, and what is optimal?


Thanks,

Ed
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Try them and see. I doubt if, on the 6br, you will be able to tell the difference between 0.002" and 0.005" as long as the neck walls are concentric and as long as the cases are sized to where the bolt handle just starts showing resistance at the bottom of the closing stroke....
 
Plus in addition you could just size 2/3 of the neck length and the unsized part will center the neck .
Just use a body die for sizing below the neck shoulder junction that will not touch any of the neck.
 
I completely disagree.

IMO YES there's a point of "too much clearance" altho it won't really affect you if you only shoot light bullets.

If this is a short-range rifle shooting 68's you can get by with horrific clearances and all you'll do is split your necks over time. The bullets will straighten themselves out in the bore. But if it's a tight twist shooting VLD's IMO you'll see degradation at any clearance larger than .002 total because of inbore yaw or cant.

Partially sizing the necks does nothing to help the problem.

opinionsby


al
 
ehkempf said:
I have three 6MM BR’s all with .272 neck. The old Lapua would give me a loaded round size of .269. The newer Lapua is now at .267, Remington 6MM BR brass also measures .267. I don’t have any Norma brass so I don’t know what size it is. Is there a point where there is too much clearance and that accuracy will be affected? What is too much clearance, and what is optimal?


Thanks,

Ed
Click to expand...

Ed
I have the same question
My 6br loaded round measures .276-.2765 with a no turn .272 chamber. I was thinking of getting a new barrel with a .270 neck to minumize the clearance. Any body that?
Guess I could turn the necks but I have a 6ppc for that and like the 6br to just load and shoot. It has done pretty good as by best group is .094 but aggs are a little inconsistent.

Ben
 
alinwa said:
I completely disagree.

IMO YES there's a point of "too much clearance" altho it won't really affect you if you only shoot light bullets.

If this is a short-range rifle shooting 68's you can get by with horrific clearances and all you'll do is split your necks over time. The bullets will straighten themselves out in the bore. But if it's a tight twist shooting VLD's IMO you'll see degradation at any clearance larger than .002 total because of inbore yaw or cant.

Partially sizing the necks does nothing to help the problem.

opinionsby


al
Click to expand...
What a wanker ! With the few thou he is talking about partial sizing will help reduce IN BORE YAW by giving better centering .
If bullets have to straighten themselves out in the bore you have distorted the bullets squarness to it's sides even when the pressure pushes the base square one side can still be left distorted compared to the other .
 
I would be interested in what a carefully done shooting test would reveal. This is the sort of thing that lends itself to that approach.

Other things to consider would be how many rounds are on the barrels, and what the rifle is used for. I am not sure that I can tell the difference between quarter and three eighths inch rifles in most field applications.

Also, periodic annealing could be done to help with the work hardening caused by this sort of clearance.
 
J. Valentine said:
What a wanker ! With the few thou he is talking about partial sizing will help reduce IN BORE YAW by giving better centering .
If bullets have to straighten themselves out in the bore you have distorted the bullets squarness to it's sides even when the pressure pushes the base square one side can still be left distorted compared to the other .
Click to expand...

??

I have no idea what you just said...... do you?

(but at least you got your chance to call me a wanker :) which is a means in and of itself.

to you)

LOL



BTW...... if what you're saying is"partial sizing helps center up the bullet"..... please explain to me 'zackly HOW this works??? How the caseneck performs the function of sealing against escaping gases while still holdingk the bullet in line...
 
alinwa said:
If this is a short-range rifle shooting 68's you can get by with horrific clearances and all you'll do is split your necks over time. The bullets will straighten themselves out in the bore. But if it's a tight twist shooting VLD's IMO you'll see degradation at any clearance larger than .002 total because of inbore yaw or cant.
Click to expand...

AL - Could you please explain what mechanics cause a light bullet to "straighten themselves out in the bore"? I had always assumed the shorter bullets were more challenged in the bore.
 
Joe Woosman said:
AL - Could you please explain what mechanics cause a light bullet to "straighten themselves out in the bore"? I had always assumed the shorter bullets were more challenged in the bore.
Click to expand...

The bullets I'm referring to as "shorter bullets," typified by the 66-68gr 6mm BR bullet w/blunt ogive, generally have a longer bearing surface than the typical VLD. The bullets with longer bearing surface wiggle into the bore with less chance of being "cocked" or having inbore yaw.

In my testing I've found accuracy with as much as .005 clearance with the 68gr BR stuff but I've concluded (OK, not concluded but strong hypothesis...) that anything over .002 will cause dispersion with typical VLD's.

al
 
alinwa said:
The bullets with longer bearing surface wiggle into the bore with less chance of being "cocked" or having inbore yaw.
Click to expand...

Ok. This does align with my thinking then. I've got very little experience with the VLD's and I didn't realize they had that short a bearing surface. The other thing that threw me was most of the short range bullets I've been shooting more closely represent a triangle than a cylinder. I'm really fond of my BIB 118's and I think the last 6ppc bullets I was working with were some Barts Wedge bullets. Both have a very short bearing length. Not sure why they shoot so darned good.
 
alinwa said:
The bullets I'm referring to as "shorter bullets," typified by the 66-68gr 6mm BR bullet w/blunt ogive, generally have a longer bearing surface than the typical VLD. The bullets with longer bearing surface wiggle into the bore with less chance of being "cocked" or having inbore yaw.

In my testing I've found accuracy with as much as .005 clearance with the 68gr BR stuff but I've concluded (OK, not concluded but strong hypothesis...) that anything over .002 will cause dispersion with typical VLD's.

al
Click to expand...

al,
Very nicely stated!
Jim
 
bering surface

I dont hav a dog in this fight,,buttt,,when touching the lands here is the ammount of shank (bearing surface) pushed into the case neck...with a .040 FB

bart 68-----.110
Euber 68---.125
BIB 65------.140
Berger 90 BT----.210
Berger 95 VLD--.160
Berger 105 VLD-.255
Sierra 107 ------.250
Lapua 105--------.290
Berger 105 Hyb--.260

This is just bearing surface--
Roger
 
Not saying there's no such thing as a .243 bullet 'yawing' in a .236/7 barrel but I will say that I'm not very open to the idea.

"Cant", if that means the bullet nose has runout relative to the bore walls, OK. I'm onboard with that.

If the terms have the same meaning, I'll buy in on both - depending on what "cant" means.

WAIT! I began to imagine that Y'all don't care what I think.....nevermind. :)
 
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Wilbur said:
Not saying there's no such thing as a .243 bullet 'yawing' in a .236/7 barrel but I will say that I'm not very open to the idea.

"Cant", if that means the bullet nose has runout relative to the bore walls, OK. I'm onboard with that.

If the terms have the same meaning, I'll buy in on both - depending on what "cant" means.

WAIT! I began to imagine that Y'all don't care what I think.....nevermind. :)
Click to expand...

Not my terms :) but if you read McCoy, Rinker, Vaughn et al.......

al
 
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