Thoughts on the Neck Carbon Ring ?

[Dusty Stevens]

Here is the typical soot I see on my necks anyone see a problem here.View attachment 1221438

Only problem i see is you only got 4 on paper. DQ in your game

 

[Dusty Stevens]

Well I thought if you use too small a bushing and sized the neck down too much, regardless of the neck thickness, it would be sloppy in the chamber and all powder/soot to flow back around the neck area, causing the soot.
Seems like I have been using neck bushings all wrong and it matters not what size they are then, as long as they are close and you neck turn the thickness down. Smile.

You can use a bushing .004 smaller or .002 bigger than youre using right now and the neck diameter will be the same down to the ten thousandth. Makes zero difference on loaded round neck diameter but makes a huge difference on target

 

[searcher]

With respect, I disagree about the clearances. I know a couple of short range group record holders, and additionally I would refer you to the series of videos on Youtube by Jack Neary. All say that for best results they want more than .002 clearance, up to .003 and that the larger clearances show up as better accuracy at 200 yards. On the end clearance, I have never seen or heard of anyone improving performance by running it that tight, a lot of theorizing, but no actual test results. In one of his videos Jack, who has been on the USA World Benchrest Championship team, said that for a PPC chamber with a maximum case length of 1.515 he trims to 1.490.

 

[searcher]

It is not as if there is a magical trim length as to why guys trim back from max - it is because one doesn't want the brass to hit the end of the chamber on firing when it stretches. When that happens, it can slightly pinch the bullet a bit, giving varied pressure - resulting in varied velocity. You always want to have a safety cushion. Some want more than others - but any increase in accuracy beyond the "no touch when fired" trim length is suspect. If one finds their rifle shoots more consistently once they trim back further than this needed amount (and .010" is more than needed for this purpose), it is likely due to no longer contending with a carbon ring they just avoided by trimming back, etc. I, along with a LOT of guys I know (and also a few world record holders) DO see the benefit in running the shoulder right up to make light contact with the forward chamber. Seems I even read this in Tony Boyer's book - and as we know- if it is written or in a you-tube video - you HAVE to believe it. Seriously though - the whole soot situation on this guy's brass is from too light of a load. The size of his bushing and how he trims his necks has little, if anything, to do with it.

 

[K22]

I'm very interested in this topic. I have one rifle, a Weatherby Vanguard, 223 Rem, 9" twist that generates a lot of soot at the base of the neck but not as much as shown in the OP's post. Still it's considerably more than all my other rifles which at first concerned me.

At first sight of this condition I considered rebarreling the rifle - no big deal since I bought the rifle for the Howa Action with the intentions of rebarreling anyway not expecting much from a cheap mass produced factory barrel and I got a real good deal on it. But decided to do some more load development and see what happens before rebarreling.

Case are full sized with standard dies to a .001 to .002" shoulder bump. Chamber length is 1.791, .031 over SAMMI 1.760 max. Best load I found was 24.0 - H4895 - 55 Nosler BT - Federal 205M primers with the components I have on hand. Bullet seated .040" off lands - lot of free bore in this rifle so this is the best I can do.

This is a winter range practice rifle, not part of my serious varmint / predator arsenal. However, after finding a load, this rifle shoots amazingly well for a cheap factory rifle, grouping in the 1/2 to 5/8" moa range. Still puzzled why it shoot this well with all that soot at the base of the neck. Looking forward to reading more about this issue. For now, I'm just going to keep shooting it since it's accurate enough for me.

 

[JMayo]

My 6bra whole neck is black ish.
My 30br has a wavy area about half way.
Seals at the shoulder is fine with me.

 

[Stan Taylor]

Only problem i see is you only got 4 on paper. DQ in your game

Thanks pal I know who my buddies are LOL

 

[cooperve]

I always believed excess OD soot on a neck was normally caused by too light of a load as “searcher" wrote.

As to case trimming I normally trim when the longest cases (in a 50 or 100 round batch) meet load manual maximum length. I bought a new 40xb-kb 22-250 caliber back in the 90’s for varmint hunting (groundhogs). When this rifle was brand new I bought a Sinclair lead/steel throat length gauge. After some 7 to 8 reloading of the brass I have never had to size the cases, they never grew close to the throat reference case gauge length.

I’m not a Benchrest shooter, but I think I'm pretty good at reloading with my knowledge and non-professional equipment. A’m I getting myself in trouble with that 40x? I don’t see it.

 

[Uncle Ed]

Have we decided if Chubbs is a carbon base life form or have we all missed the target.

 

[jelenko]

In an AR, what would cause some rounds to come out with heavy soot all over it but the vast majority to have much less? I.e., 1 in 40 or 50 rounds?
Load being 23 ish of 8208 with a Hornady 75gr. Wylde chamber, 24" barrel with rifle length gas system.
Usually occurs when shooting around 1 shot per 3 sec.

Thanks

 

[338 dude]

Here is the typical soot I see on my necks anyone see a problem here.View attachment 1221438

It seems the soot line varies slightly at the neck/shoulder is that the problem you’re speaking of or am I seeing things

 

[Stan Taylor]

It seems the soot line varies slightly at the neck/shoulder is that the problem you’re speaking of or am I seeing things

Honestly I don't have a problem with chronograph numbers or accuracy basically I'm just asking isn't it normal to have soot on case necks I've always had some sort of soot on necks every since I started shooting competition.

 

[mikecr]

You can use a bushing .004 smaller or .002 bigger than youre using right now and the neck diameter will be the same down to the ten thousandth. Makes zero difference on loaded round neck diameter but makes a huge difference on target

Proper bushing down sizing makes no more difference to neck tension as it does to seated neck thickness.
For either, extra down sizing is just extra upsizing with bullet seating.

Go ahead and try it, see for yourself. Everybody here should do this:

Bushing size down two necks with same thickness to no more than intended seated bullet bearing.
With one, size down 2thou under cal, the other 4thou under cal (both actual, after springback).
Seat bullets, measure neck ODs -THEY MEASURE THE SAME.
Pull the bullets, measure neck ODs -THEY MEASURE THE SAME.
So bushing size did not change neck thickness nor apparent neck tension(which is springback).
Is that right? Yes it is.
While you're doing this testing, you can go ahead and measure seating forces, where you'll see that it obviously takes more force to seat into 4thou interference than 2thou. But then when you re-seat bullets and fire with this difference -THE MV AND TUNE REMAIN THE SAME.
So seating friction does not change muzzle velocity, which makes sense -because it did not change neck tension. The springback that grips seated bullet bearing, always remained the same.

If you want to change neck tension, then affect what neck tension is: springback force times area gripped by that force.
The force is what necks provide with their ~1/2thou of spring back.
The area is adjusted by sizing LENGTH.
If you bushing set interference at 1thou under cal for 1/8" of necks, you will produce a tension that is lower than a bushing adjusted for sizing 1/4" of necks. And you will see a difference in MV.
As earlier testing above showed, it does nothing good to downsize an excess amount, which bullet seating will just undo. So pick a bushing to cause no more than 2thou interference which will spring back outward a bit to ~1.5thou interference(still more than necks spring back to from cal).
Then ideally, you would mandrel expand, at cal, like a bullet would anyway, and seat bullets into the spring back interference. I call this pre-seating.

As far as 'sine wave' sooting shapes meaning anything? Still waiting for an explanation & test that supports it.. I'm confident that just as many, and likely way way more, shoot fine with different shaped and amounts of sooting.

 

[Ccrider]

So, what you are saying is decreasing neck size by using smaller bushings have no effect on tune or the target? @mikecr, hope you have your flame suit on.

 

[Dusty Stevens]

So, what you are saying is decreasing neck size by using smaller bushings have no effect on tune or the target? @mikecr, hope you have your flame suit on.

It does affect the tune. Its how BR shooters tuned before tuners

 

[Dusty Stevens]

As far as the neck carbon sine wave- tony boyer speaks about it in his book and i know when my gun is shooting its smallest it will have the sine wave. It will even have 3 waves on a 3lug action. Neck clearance, tension and load is perfect or real close when you see it. Any slower or faster powder than the case wants it goes away too

 

[jackieschmidt]

So, what you are saying is decreasing neck size by using smaller bushings have no effect on tune or the target? @mikecr, hope you have your flame suit on.

If you seat a bullet with .001 interference, it will take less force to pull it than one seated with a .003 interference. The small amount of force difference is what affects the tune in extreme accuracy applications.
As for the Sine Wave shape of the carbon ring, all we are saying is that is what appears on the neck when you reach that (ideal) loaded round to chamber neck clearance of around .002 inch.

a good example is with my 30 BR, I use an extremely light neck tension with the seating depth and powder charge I use. If I go to a smaller bushing, it turns a .150 rifle into a .250 rifle. I could probably adjust other parameters of the tune to get the accuracy potential back, but I like the really light neck tension.

 

[Chubbs]

Chubbs

My guess is the sharp carbon line on your necks is caused by a bushing that is not sizing down all the way to the neck shoulder junction. And if you did not use a non-bushing full length on your cases before neck turning you have pre-formed donuts below your carbon line.

In WWII terms you are fighting the battle of the bulge.

And your wife would say you have ring around the collar.

Hi
Not used a bushing die. Have the same ring on turned and unturned necks.

In regards to a light load I am running at 2600fps on 139 GRN bullet for 6.5 CM.

 

[Ccrider]

While you're doing this testing, you can go ahead and measure seating forces, where you'll see that it obviously takes more force to seat into 4thou interference than 2thou. But then when you re-seat bullets and fire with this difference -THE MV AND TUNE REMAIN THE SAME.

I believe it changes tune. @mikecr says it dies not. Maybe he will post some targets to demonstrate it. I know my targets generally change as I increase or decrease bushing sizes.

 

[rogina]

Here is the typical soot I see on my necks anyone see a problem here.View attachment 1221438

Nope. Wipe it off and keep on shooting.