Neck clearance?

B

bluechip

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I have a 6PPC with a .262 neck. I am about to neck turn a batch of cases. .009 wall gives me a loaded cartrige that measures .260 neck or .002 under barrel neck dia. Before I start turning, is .002 clearance about right?
 
Bluechip

I think nowdays the general consensus is don't go any tighter than .0015 and no looser than .002, and you will be fine.

The main thing is to get them all the same, as different neck wall thickness canaffect neck tension. Consistant neck tension is recognized as one ofthe contributing factors in achieving the level of accuracy that is demanded in Competitive Benchrest...........jackie
 
Neck thickness...

bluechip...Double check your calculated loaded round diameter.
Measure your actual bullet diameter---not all bullets are the same.
Measure over the pressure ring(if a flat based bullet). Take this measurement and add to 2X the neck wall thickness. Using the nominal figure
of .243" for bullet diameter + 2X .009"(.018")=.261". Please correct me if I'm wrong. I've measured some as small as .2429" to as much as .2435". I turn my to .0086" and have had no problems using a variety of bullets.
Good luck...good shooting.....gpoldblue
 
neck

Jackie, Gpoldblue, thanks for the info. I would think as the neck size of the cartrige fits with more than .002, accuracy would start to diminish. What is the problem or danger in trying for a closer fit like .0005-.001?
 
An explosion,

ruptured case, lost eye with even the slightest variation or miscalculation or FUBAR in bullet size or neck growth and thickening unobserved. :(
 
Bluechip

Quite a few shooters used to use what is call "fitted necks", that is, necks fit close enough to where no sizing was required, the natural springback of the brass would be enough to grip the bullet. That was back when the 6PPC was shot at 3150 fps, using powders like the old GI322, 2015, T-32, etc.

Benchrest has sort of evolved into a different game, N133, 70,000 psi loads, full length sizing, looser necks, mainly to avoid any pressure spikes that could be a result of a bullet no releasing as freely as others.

Many shooters think this is all insanity, but all you have to do is look at the aggs that are being shot with Benchrest taking this current course.

In short, since there does not seem to be any accuracy advantage to necks that have .0005 or so clearance, shooters choose to avoid any problems by going with a little more..........jackie
 
Wow!

jackie schmidt said:
Quite a few shooters used to use what is call "fitted necks", that is, necks fit close enough to where no sizing was required, the natural springback of the brass would be enough to grip the bullet. That was back when the 6PPC was shot at 3150 fps, using powders like the old GI322, 2015, T-32, etc.

Benchrest has sort of evolved into a different game, N133, 70,000 psi loads, full length sizing, looser necks, mainly to avoid any pressure spikes that could be a result of a bullet no releasing as freely as others.

Many shooters think this is all insanity, but all you have to do is look at the aggs that are being shot with Benchrest taking this current course.

In short, since there does not seem to be any accuracy advantage to necks that have .0005 or so clearance, shooters choose to avoid any problems by going with a little more..........jackie
Click to expand...


You are saying that 6PPC's are currently using 70,000 psi? I'm a novice to 6PPC, and I am using 27.5 gr. of H322 behind a 68 gr bt. I would guess that my pressures are in the 40,000 range, so what kind of FPS does 70,000 produce?
 
bluechip said:
I would think as the neck size of the cartrige fits with more than .002, accuracy would start to diminish. What is the problem or danger in trying for a closer fit like .0005-.001?
Click to expand...

Ok I may be wrong here but I never heard that running say .003 or even .004" neck clearance was inaccurate. The reason you do not want to do that is it works the brass unnecessarily and that shortens it's life and it starts to develop cracks . Well I guess you could say that leads to poor accuracy but I just call it case failure more than just inaccuracy . If you are jumping your bullet I guess it could also lead to the loaded round laying off to one side in the chamber which would not help.

Dick
 
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Do The Math

It is not uncommon for shooters, (quite a few who are "at the top of the game"), to push a 66-68 grn bullet 3400-3450 fps out of a 21 1/2 inch barrel.

I suspect that is getting into the neighborhood of 70,000 psi.

That might sound scary, but keep in mind, the standard Factory Remington Load for a 300 Ultra Mag is 60,000+psi. And that is in what amounts to a standard Rem 700 action, not a tight tolerance Benchrest Action.

However, you do not need to go there. As has been said many times on these Forums, Shooters participate in Benchrest using loads that never top 3250. ...........jackie
 
I know of one top shooter that shoots for .00275 total clearance, another fellow that holds at least one record that works in a range between .002 and .003. A third shooter who is near the top of the game uses .003. There is a tendency, in Benchrest, to think that if tight is good, tighter is better. Given how these fellows shoot, I doubt it.
 
Which leads this person to ask...Why have so many settled on a .262 neck in the PPC. I would really like to hear a good. beleivable story concerning this.
Mark
 
Using a .262 neck and greater clearance like .0025 or .003 leaves paper
thin necks that don't hold up well. With the Lapua brass used now, .262
is generally arrived at in two or three turning operations, not a lot of fun.
 
Bob Kingsbury said:
Using a .262 neck and greater clearance like .0025 or .003 leaves paper
thin necks that don't hold up well. With the Lapua brass used now, .262
is generally arrived at in two or three turning operations, not a lot of fun.
Click to expand...

Exactly...which leads me to ask...is there an accuracy oriented reason that a good percentage of BR shooters today that use the 6PPC...use the .262 neck versus say a .268 or .269 neck?
I am looking for a "good reason" to jump through the hoops of turning brass in a 6 PPC to .0086 or so neck thickness rather than .0116 or therabouts with a .268 chamber neck?
 
Some shooters are using a .269 neck now.

If I am not mistaken that is about where the current Lapua brass will clean up now.
As to your question why it is still done this way regarding a .262 neck.
I can give you several reasons

1. the original reason above all was concentric necks
2. as Boyd said to get those we had Sako brass and to get a clean turn it was turned to end up with a .262 neck.
3.If you ever notice the age group of most of the shooters you will see we are old and you know old people dont like to change their ways or traditions:eek:
4. as Reptavia said "TRADITION"

All kidding aside some of the best shooters are now using a .269 neck as that seems to be where the l Lapua brass cleans up, at least thats they way I understand it.

Maybe Jackie or one of the others will chime in and give us more info.

If I remember correctly Norma or Hornady has now come out with some 6PPC brass that is sounding promising as well. I dont know where that will turn to though.
 
chrono

In a few days I'll chrono my 6PPC using 27.5 gr of h322/68 gr bt. I'm sure some of you here already know what FPS I'll get. I'm happy with the groups I'm getting and probably will never stray into the 'twilght zone' of ultra high pressures because it just seems hard on everything like the rifle and cases.
 
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