Short / long range BR neck clearance?

[X Count]

I have a barrel that isn't shooting as consistently as I would expect from the things I've tried up to this point. I'm starting to consider potential issues outside of powder, seating and charge tuning.

One thing is neck clearance. This is currently running .002" clearance. With cases that are annealed every firing I'm getting very slight resistance when inserting a projectile in a fired case. The resistance is consistent on every case.

I understand that the rule of thumb is a projectile should be able to slide freely inside the neck. Question is to those that are at the pointy end of short range / long range BR, are you still using this generic rule of thumb, or are you working down into this territory and getting consistency with all other things being equal?

 

[boltfluter]

A caliber may help with getting a more precise answer. 6PPC can be much different than a. 284 Winchester, as to what people prefer clearance wise. Good shooting.
Paul

 

[AlNyhus]

Before going much further...describe how you're measuring your neck clearance. -Al

 

[BoydAllen]

You may know all the details about your rig, but we have no clue. You may be looking at the wrong thing, and one of us might have a good suggestion about where else to look but with virtually no information that is not going to happen.

 

[X Count]

Cal-6.5x47
Barrel - Bartline 1.25" parallel 30" 1-8
Chamber- .293 neck
Loaded round - .291 measured with mitutoyo digital micrometer
Action - Bat M
Scope - NF Comp
Stock - PR&T F Open
Rest - SEB neo

The rest of the platform is proven with multiple other barrels and cals. I've shot 6.5x47 before BUT with a different reamer that had a bigger neck diameter and slightly longer throat. My ES is up in the 25fps range and my groups aren't consistent even at 200-300yds where ES doesn't have a huge impact. I've explored 4350 and varget which shows glimmers of hope then shoots 1moa elevation. I'm leading toward there being and issue with the chamber or maybe just unlucky with this barrel.

 

[AlNyhus]

Thanks for the additional info. Have you verified the chamber length and compared it to the case lengths?

 

[BoydAllen]

For short range benchrest, some very good shooters believe that they have gotten better results at 200 yards by increasing their loaded round neck clearance to around .003. In long range benchrest I have read of tests where fellows increased neck clearance beyond that by quite a bit for larger calibers (than 6mm) and have not see any accuracy issues caused by the increased clearance. Why not re-turn a few cases for .003 to .004 clearance and test?

 

[Bill Norris]

Jack Neary a HOF Short Range BR shooter says he wants .003 total neck clearance with his 6PPC.

 

[Tim Singleton]

Clearance is important for sure 002 to 003 is good
seating depth is the thing that is a killer. It can cause you to loose your mind
keep working at the seating depth until you find a place that is consistently good

 

[X Count]

Thanks for the additional info. Have you verified the chamber length and compared it to the cae lengths?

No but worth a check!

 

[X Count]

For short range benchrest, some very good shooters believe that they have gotten better results at 200 yards by increasing their loaded round neck clearance to around .003. In long range benchrest I have read of tests where fellows increased neck clearance beyond that by quite a bit for larger calibers (than 6mm) and have not see any accuracy issues caused by the increased clearance. Why not re-turn a few cases for .003 to .004 clearance and test?

Yep this is the info I was looking for to determine if I should increase that neck clearance. Even amongst those that are controlling their tolerances well, they are not seeing a decrease in accuracy with more clearance. Reason I haven't done it already is price and availability of brass if it has a negative effect.

 

[Bill Norris]

For short range benchrest, some very good shooters believe that they have gotten better results at 200 yards by increasing their loaded round neck clearance to around .003. In long range benchrest I have read of tests where fellows increased neck clearance beyond that by quite a bit for larger calibers (than 6mm) and have not see any accuracy issues caused by the increased clearance. Why not re-turn a few cases for .003 to .004 clearance and test?

Erik Cortina F-class shooter has gone with even more neck clearance according to his description of his chamber sometime back on a podcast. Must be working well for him.

 

[6MMsteve]

Erik Cortina F-class shooter has gone with even more neck clearance according to his description of his chamber sometime back on a podcast. Must be working well for him.

yep he's winning or at the top most matches he's doing something right

 

[Clancy]

I absolutely will not shoot with less than .003 in anything anymore. I buy enough brass for several barrels and have a Reamer made for .004 clearance. Running .0015-.002 caused me nothing but grief.

If it makes you feel any better, I shot several hundred rounds of leftover 6BR brass turned for a .268 (.2645 loaded) in a .272 last year and the accuracy was incredible. You’re CERTAINLY not going to hurt anything turning a little off of your brass.

All that being said, I still consider seating depth to be the single most important factor in reloading.

Lastly, there have been a LOT of BAT actions with pin drag the last couple of years, but you say the platform is proven so that shouldn’t have a thing to do with it.

 

[Bill Norris]

Shooting LND @ .291 in a .298 chamber neck gives me 1/4 MOA and sometimes less in my 260AI. Of course I have brass that gives .293 - .294 LND as well. BUT, I don't feel .007 is too much clearance due to these results.

 

[Clancy]

Shooting LND @ .291 in a .298 chamber neck gives me 1/4 MOA and sometimes less in my 260AI. Of course I have brass that gives .293 - .294 LND as well. BUT, I don't feel .007 is too much clearance due to these results.

Not at all. I’m lookin at building a straight .284 and thinking .006 clearance

 

[6BRA]

I had a 6.5x47 2 years ago running 130s at 2950 with H4350. It shot very well. .005 to .006 neck clearance. Annealed every firing. Neck turned factory 700s for years. Big neck clearance. Never annealed at that time. I wouldn't limit myself to .002 or .003. What is your shoulder bump like?

 

[X Count]

Erik Cortina F-class shooter has gone with even more neck clearance according to his description of his chamber sometime back on a podcast. Must be working well for him.

I think that for f class in the volume that Eric is shooting you need to make compromises. If your loading 400-600 rounds for and event, your going to be shooting multiple 20 shot strings between cleaning, shooting in varying wind conditions, not reloading between relays and shooting at a 1moa target then the point of diminishing returns is going to be different to that of someone trying to achieve SR / LR BR accuracy.

We all know there comes a point where the nut behind the butt takes over and the more rounds you shoot and the more matches you attend the better you get.

 

[rebs]

is neck clearance the same as neck tension ?

 

[Bill Norris]

is neck clearance the same as neck tension ?

No. Neck tension is determined by the amount of tension applied to the bullet by the case neck. Neck clearance is the amount of space between the case neck and the chamber neck.Two entirely different items.