Neck Clearance

[Cybra]

Hello to all!

Hopefully a few of you might offer me some insight; I could certainly use it. What I would like to know are some numbers on neck clearance that some of you utilize. Currently I'm running a .338-378 with about .0015" clearance *per side*, and am thinking when the throat goes to hell <the eneviditable, sadly> I may try something tighter. In the meantime, and more pressing to me, is another project {it's a mouse-gun, but no laughing now!}, based on a 6PPC with a sharp shoulder <40 degree>, firing 95gr VLDS. I am thinking a half-a-thou per side. So what do you fellows run? I admit, I like things on the tight side [don't post my comments on FriendFinder, please

], but would truly appreciate a few experienced comments. pros, cons, etc. Primarily, this will be a bench number, and I'm a meticulous cleaner, so blowing my digits off shouldn't occur....

Thanks, guys. One of these days I'll get smarter and can help inform some of the goofs like myself!

Dave

 

[mindcrime]

Bruce Baer runs .0015" clearance per side in his 1000 yard guns, so your clearance in your super thumper is spot-on. But wait, you asked what we are running. I have both a 6mm PPC with the standard .262 neck and a 6mm Remington Ackley Improved with a .266 neck. I run .0010" per side in each and it seems to work very well in my rifles. I also run .003" tighter bushings(.257 and .261 respectively) in my Wilson hand dies. You can have my $0.02.

 

[daveosok]

Is their any correlation between case capacity and velocity when setting up for proper neck clearance?
What determines how much you need and is their a standard to use when figuring out the proper clearance?
As I understand it, neck turning allows consistant releasing of the bullet when fired, thus a few things happen as I'm thinking here.
One with consistant release pressure I think that youll see less extreme spreads of velocity?
Two if the powder performs consistant youll end up with consistant barrel harmonics?

Any merit to my thinking?

 

[Guest]

[ 07-12-2003: Message edited by: S1 ]

 

[Len Backus]

S1

You seem to be a measuring kind of a guy and I like that. In your opinion, at 1,000 yards, how much is group size affected by not neck-turning? How much would an otherwise (let's say) 10 inch group be improved by turning?

 

[BountyHunter]

Cybra,

On the 6mm BR, I am building a 6mm BRH now (shoulder moved forward .200 and 45 degree shoulder and .265 neck). This design is similar to the popular 6mm BS (Baby Shehane). It will be used with 95-105 VLDs from JLK in a 28" HV taper Spencer barrel with 1-8 twist. My plan is to be .0005-.0007 per side with Lapua brass. Good 600 yd BR gun, egg shoot and backup LG.

Dave Kiff made the reamer. My 1000 yd guns I set up to have .001 or less on each side. Intersting side note on clearance. Some of the early top dog LR BR shooters shot magnums with .003 clearance on each side as they thought that was best way to shoot magnums and consistently won. Now the same guys are using standard BR clearances of .001 and group sizes has shrunk by 50% on average at least. 2-3 years ago, you could win IBS LG with a 6" group consistently, now it takes 3-4". HG would win with 9-10" now you must shoot 4-6"

Personal opinion is that tight neck turned cases are more uniform, give more uniform release, MV, SD, ES etc. The LR BR shooters have found that we can control the tolerances as tight as the shortrange BR shooters with good tools, loading techniques and cleaning. Look at the results at the last nationals on group sizes for both LG and HG. Quality tools and procedures such as K & M neck turner are key. I have tried all of them and his is the absolute best (in my opinion). You can turn to .00002 precisely. His tools are a top choice for BR shooters.

Good luck

BH

 

[Mysticplayer]

Cybra, I too shoot a 6BR with a tight neck and it is one of my best shooters. One thing to consider, are these rifles going to be hunting? If so, are you going anywhere where rain/humidity or dirt could be an issue?

Although we have done everything to make our rifle chambers and ammo clean, a little bit of moisture on the necks/chamber due to rain or condensation while out in the field could now cause clearances to go to zero. Water does not compress very well.

I like tight necks for my BR and varminting rifles where I can control everything but get a little nervous if used in a "working" rifle.

In Canada, some of the best places and times to hunt get you in pretty wet, cold/snowy or mucky conditions. I neck size my brass and use normal SAAMI neck dimensions. Accuracy is around 1/2 MOA which seems adequate for any of the big game hunting I am likely to do.

Something to think about...

Jerry

 

[Guest]

[ 07-12-2003: Message edited by: S1 ]

 

[Cybra]

Wow!!

Thanks to all that have replied--you know you're on a good forum when you wake up, work-out, take lunch, check your messages and find you have seven replies!

You guys have really helped me out! With the modified 6PPC I'm doing, I am thinking about .0005"-.0007" would be what I would like to do, per side, although, as Jerry pointed out, moisture concerns have arose. I will be shooting in MN by the time this weapon is built, and I prefer to shoot fall, winter, and spring--in other words, until God's gift to man <i.e. insects> begin to appear! I don't know how much of a problem condensation will present; however, I do not typically load hot. In fact, I'm making the barrel 27" long instead of 25" for two reasons--added velocity with compressed loads of N135 or N140, and a reduction in muzzleblast to make things quiet when hunting with lighter bullets and reduced charges of faster stuff {probably N120}. S1, Dave; As for turned necks, and the word "immaculate"--I may leave that one to Madonna; I'm trying to turn them perfectly, but about .0001-.0002" seems to be the average in consistancy. Mindcrime--Mr. Baer is probably the fellow I'm going to ask to put this together; I'll have to let everyone know how it goes, although...by the time I, personally, get enough money together to spin the big Wheel, most of you won't even know what the hell the topic started out about, anyways!

I sure as hell won't--I can't even remember important stuff like family birthdays!! <forgot my own, this year, and I'm 23!> Anyhow, I appreciate you fellows taking the time; I can try and share what I know, but I'm still so damned green, there isn't much to that!

Has anyone, on a side note, read a book by Harold Vaughn titled Rifle Accuracy Facts? I don't yet understand all the physics he lists in the book, but do think the main concepts are very...thought-provoking.

Dave

 

[Cybra]

Bounty Hunter

I was going to e-mail you, personally, but it refuses to give me an addy; guess it doesn't trust me...

It sounds like we are on similar endeavors. I have read that a 45 degree shoulder is optimum with certain cases, with the possible exception of that design that McPherson and some other fellow are trying [I can't recall the specified name of the shoulder configuration, but I think I read about it on here. The case is the 6mm Thermos Bottle, I think.] What I am probably going to do is push the shoulder on the necked-up .220 Russians I have back until I get either a 40 or 45 degree angle <still debating>, which should lengthen the neck. from there, I may keep the long neck, who knows. I won't aid accuracy, but it might aid throat life a slight amount. The heaviest bullet I will shoot, and the primary bullet, will be Berger's 95VLD.
Currently I'm running a Sinclair neck turner, with mandrels I turned myself. They seem to work nice; I think the reason I'm get one to two ten-thousandths variation from one box of 100 to another is mostly due to either a.) mandrel gets warm, b.) lube build on mandrel, but I doubt it, or maybe c.) where it has something to do with how they were necked up [I use a two-step process, but just recently adjusted the expander so it was more "loose" and could self-center on its own. Seems to have helped.] Anyhow, thank you for replying as well.

Dave

 

[dbhostler]

When I run a batch of brass through, "the treatment", I usually settle on about .0015" under chamber diameter. This is about as close as I feel I can safely go. I have also found that anything less than a perfectly cut and clean chamber can cause problems. I polish the necks with 1200 grit and use what my gunsmith calls a seating depth checker. This is simply a 1 to 2 inch piece of barrel that has been cut with the same reamer used to cut the chamber of your rifle. If the round inserts in this easily, you're good to go, if not, you have a problem and should not chamber it. Actually this piece should more accurately be described as a go-no-go gauge. I also mic all bullet diameters for even .0005" over can cause problems. I do love tight chambers, and all this hassle really is fun to me. Just my 2 cents.
Good Shooting,
db

 

[Len Backus]

S1, thanks.

I've never turned necks or even measured them but I'll check the dimensions now. Usually my verticle dispersion is at just about 1/2 moa out to 500 yds. Seems to open up a little further out.

I have just ordered a true 1000 yard benchrest gun, finally, so I will be learning to turn necks and do all that other exotic stuff.

 

[Cybra]

Hey, DB

That's a good idea--I like that suggestion. It's perfect timing, too, because I'm in the process of talking with Mr. Manson on some options with the reamers themselves. I'm really, really inexperienced at designing "new" cartridges; I'm sure a lot of people have tried this all ready, JUST about. Naturally, I have to be an odd-ball, and go specifying weird neck dimensions, and crazy throat angles.

But the suggestion does seem to flip a few switches on, so thanks.

Len I'm more in your boat, I think; prior to contracting that horrible disease I've seen referred to as LRH, I never turned much for necks, either. One thing I am sure of, though; that disease....I think it gets more money donated to the "cure" of it by some outside folks than any other....

Dave

 

[dbhostler]

Cybra, if you have your smith make one of these go-no-go things, have him mill one half of it off so you can see the case shoulder, neck and bullet. This way you can see what's really going on inside your chamber. It will also tell you when you need to trim the length of your cases back.
db