Carbon pattern on necks

[Nude nut]

Hi,
Could somebody out there explain what causes this and Is it good or bad Im getting a very clean sinewave from the star of the neck to the rim I shall try post pictures.

Cheers Trev.

 

[Dusty Stevens]

It is explained in tony boyers book. That is perfect neck clearance and it is a representation of your bolt lugs

 

[Nude nut]

It is explained in tony boyers book. That is perfect neck clearance and it is a representation of your bolt lugs

Thank you Dusty.

Cheers Trev

 

[SHootSTraight22]

From what I've seen your necks look perfect... If it could get any better it would be the sine and cosine wave starting more towards the center of the neck I think??? If you want to experiment some try using a bushing .001 larger and one .001-.002 smaller to see how the ring changes as well as your groups.. I think as you go tighter the sine and cosine marks go away and you will get more of a ring.. If you go larger bushing you start getting the ring down into the shoulder area.. This all has to do with when the bullet releases and when the case seals the chamber off from what I've seen... I wished I knew what that book he mentioned says about all this..

 

[savagedasher]

It tells me your case neck is soft enough that it is sealing and not letting pressure go down the neck . As it is shot more the neck will harden and the neck will get more carbon on it
Larry

 

[Tim Singleton]

It's a more a function of the amount of neck to chamber clearance than anything.
Yours look good

 

[Nude nut]

Those cases were virgin lapua 308 cases chamfered and deburred then dipped in graphite then I ran them through my expander die loaded them up and used them saturday at 900yrds and won that shoot.
They had about an inch vertical on target for me thats pretty good it was my third shoot at 900yrd so was happy last week at 900yr practice I had some that I sized necks down with nk bushing die and tried the turning mandrel instead of the expander mandrel my mate shot those in my rifle and got same result but no pattern on the neck.
May play around with this some more I think.

Cheers Trev.

 

[kolar55]

It's a more a function of the amount of neck to chamber clearance than anything.
Yours look good

++a bunch If there's not enough clearence there will be a ring all the way around about a third to half the way down the neck. That ring could be present until the cases are reloaded up to about 5 times and then should be looking like what you have.

 

[savagedasher]

++a bunch If there's not enough clearence there will be a ring all the way around about a third to half the way down the neck. That ring could be present until the cases are reloaded up to about 5 times and then should be looking like what you have.

The only time mine changes is when it needs to be annealed .Larry

 

[ireload2]

It is a function of brass temper/anneal, clearance and pressure rise.
I have a lead bullet rifle I shoot with interference at the neck. There is no soot at all.
Then a bench rest rifle I shoot makes a ring around the neck about .100 down.
Shoot 50 different rifles and see how many variations you get.

 

[savagedasher]

It is a function of brass temper/anneal, clearance and pressure rise.
I have a lead bullet rifle I shoot with interference at the neck. There is no soot at all.
Then a bench rest rifle I shoot makes a ring around the neck about .100 down.
Shoot 50 different rifles and see how many variations you get.

I have a friend who shoots lead bullets and he breach seats and doesn't have a carbon mark
But they are straight wall. Larry

 

[ireload2]

My example is a 38-55 which is a cartridge with a poor chamber and bore relationship per the wonky SAAMI drawing.
That happens when you try to document an 1876 Ballard cartidge design.

I have a friend who shoots lead bullets and he breach seats and doesn't have a carbon mark
But they are straight wall. Larry

 

[gsg5pk]

Those cases were virgin lapua 308 cases chamfered and deburred then dipped in graphite then I ran them through my expander die loaded them up and used them saturday at 900yrds and won that shoot.
They had about an inch vertical on target for me thats pretty good it was my third shoot at 900yrd so was happy last week at 900yr practice I had some that I sized necks down with nk bushing die and tried the turning mandrel instead of the expander mandrel my mate shot those in my rifle and got same result but no pattern on the neck.
May play around with this some more I think.

Cheers Trev.

What is your load info for match?

 

[Nude nut]

What is your load info for match?

My load is 45gr of 2206h/h4895 lapua palma brass br4 primer 155.5 berger fullbore 10thou of the lands chamber is .40 freebore cbto 2.205 and oal is 2.912 muzzle velocity is approx 3000 fps.
When I first cronyed this load at 10thou in I only shot 6 rounds and speeds were,
3030
3033
3032
3035
3030
3033.
Have not checked since bullet depth change and barrel is 32in.

Cheers Trev.