Proper neck clearance
- Thread starter CoverDog
- Start date
Mr friend, it is your call.
The clearance is not a reflection of the bullet size but the clearance of loaded round within the finished chamber size, for example my 7/300 WSM is turned to give me .310" on a loaded round, to fit into a .312" chamber.
You might find life a little easier if you settle of a .004" clearance on your loaded rounds i.e. neck to to obtain .332" on a loaded round
The clearance is not a reflection of the bullet size but the clearance of loaded round within the finished chamber size, for example my 7/300 WSM is turned to give me .310" on a loaded round, to fit into a .312" chamber.
You might find life a little easier if you settle of a .004" clearance on your loaded rounds i.e. neck to to obtain .332" on a loaded round
Jay Christopherson
Not An Admin
On my match rifles, I run .0015" to .002" (1.5 thou - 2 thou) of clearance. For my 6 Dasher with a .269 chamber, I turn to .2675, loaded. On my 7WSM, I run a much looser tolerance (no turn), closer to .004", but it's not a match rifle either. If it were, I would have had it cut tighter.
This is just my opinion, but if that 300WSM is a match rifle and it were mine, I would probably turn the neck down so that a loaded round was .334. If it is not a match rifle, I would take Yellow11's advice.
This is just my opinion, but if that 300WSM is a match rifle and it were mine, I would probably turn the neck down so that a loaded round was .334. If it is not a match rifle, I would take Yellow11's advice.
Myself and a few others have found with 7mms and 30s, that the .002" clearance which most 6PPC shooters swear by, was not enough, causing verticle so we switched to .003" clearance.
I know with my 22BR, 6PPC and 6 Dasher with .002" clearance, a bullet is a firm slide fit in a fired case. With 7mms and 30s, it seems .003" seems to give the same feel.
I know with my 22BR, 6PPC and 6 Dasher with .002" clearance, a bullet is a firm slide fit in a fired case. With 7mms and 30s, it seems .003" seems to give the same feel.
couple years ago, I had a discussion with noted gunsmith and benchrest shooter Gary O'Cock about neck clearance. His opinion was that "accepted norms" were changing in the direction of greater clearance for safety and performance. Sure a tight neck allows you to reuse your brass many many times. but it is not a requirement for accuracy and safety is enhanced with more clearance. I think .004-.006 total clearance is good for highpower, hunting, long-range. No experience with benchrest, but it seems that people are moving away from super-tight neck dimensions.
You can go either way with good results. But neither direction is free.
I like tight clearances everywhere. It's easy on the brass so reloading is easier.
My loads stay put over time, with little sizing, trimming, annealing, or brass turnover.
But it takes more planning/attention on the front end to do this.
I can suggest that fitted neck clearances(<1.5thou) shoot atleast as well as any greater clearance. I also believe it reduces ES, as there is nearly instant neck sealing(as observed sooting is way less).
But I couldn't prove it makes a gun more accurate amidst the noise of other factors.
I like tight clearances everywhere. It's easy on the brass so reloading is easier.
My loads stay put over time, with little sizing, trimming, annealing, or brass turnover.
But it takes more planning/attention on the front end to do this.
I can suggest that fitted neck clearances(<1.5thou) shoot atleast as well as any greater clearance. I also believe it reduces ES, as there is nearly instant neck sealing(as observed sooting is way less).
But I couldn't prove it makes a gun more accurate amidst the noise of other factors.
BoydAllen
Gold $$ Contributor
Some credible long range shooters, who shoot .30 caliber, have written that they get better results with more clearance, as much as .005, if I remember correctly.
I have had conversations with top level short range benchrest shooters that have gone to clearances (measured over the pressure ring) in the area of .0025 to .003. If you want to see a good discussion of this. do a search, on YouTube for Jack Neary. Because of it's length, his presentation is divided into six parts there.
Until recently, I had been using something in the area of .001 to .0015 (6PPC). After listening to my betters, I am now recutting my necks to produce .0025 with my largest bullet. This is not to say that matches have not been won with tighter clearances, just that I pay some attention to what some of the guys at the top of the game are doing. To answer the original question, it is my impression that it may be desirable to increase clearance as caliber increases. and that overall the benefit may be in getting a more uniform bullet release. Of course, I could be wrong.
I have had conversations with top level short range benchrest shooters that have gone to clearances (measured over the pressure ring) in the area of .0025 to .003. If you want to see a good discussion of this. do a search, on YouTube for Jack Neary. Because of it's length, his presentation is divided into six parts there.
Until recently, I had been using something in the area of .001 to .0015 (6PPC). After listening to my betters, I am now recutting my necks to produce .0025 with my largest bullet. This is not to say that matches have not been won with tighter clearances, just that I pay some attention to what some of the guys at the top of the game are doing. To answer the original question, it is my impression that it may be desirable to increase clearance as caliber increases. and that overall the benefit may be in getting a more uniform bullet release. Of course, I could be wrong.
I use a tight neck chamber in 284 Shehane. The chamber neck dia is 0.313 and my loaded round is 0.310 giving 1.5 thou clearance. As I use the rifle for F class here in the UK I did not want anything too tight and could get away with 2 thou clearance but my gunsmith Grant Taylor reckons 1.5 thou is good to go.
BoydAllen
Gold $$ Contributor
The usual standard for quoting neck clearance is ID of chamber minus OD of loaded round. (If the bullet has a pressure ring, measured over that.) Using that convention, and your numbers, you have .003 clearance. (When I wrote of neck clearances, that is what I meant.)
I have moved away from tight necks (0.002" or less). I had a 6BR that ran about 0.0015" and it developed doughnuts and generated a little pressure. I cut the doughnut back and was running about 0.0025" and the velocity came up.
I have a 6SLR that refused to group until I cut the brass back to 0.004" and it has shot much better. My best grouping gun (a 308 Palma rifle) is about 0.009"
To me diameter is not the variable of interest when talking neck clearance, it's the relative change in cross-sectional area. Very similar due to small changes and similar diameters, but, it does vary with bullet size.
Right now If I'm building a gun I'd say 0.003"min for a 6mm and 0.006" min for a 308 .
Just my $0.02
I have a 6SLR that refused to group until I cut the brass back to 0.004" and it has shot much better. My best grouping gun (a 308 Palma rifle) is about 0.009"
To me diameter is not the variable of interest when talking neck clearance, it's the relative change in cross-sectional area. Very similar due to small changes and similar diameters, but, it does vary with bullet size.
Right now If I'm building a gun I'd say 0.003"min for a 6mm and 0.006" min for a 308 .
Just my $0.02
Donuts aren't caused by neck clearances.
With a 6br they're caused by heavy FL sizing.
As far as bullet release, it takes no more expansion of a neck to release a 30cal bullet than a 17cal bullet. And provided there is any clearance at all, you should not have any pressure issues.
Turning necks thinner would have reduced neck tension and that may have resulted in a better shooting load for you..
But there are plenty of shooters doing well without turning for larger clearances.
If you have excess runout, and jam bullets, you might also benefit from greater clearances.
I don't know, it hasn't been proven.
With a 6br they're caused by heavy FL sizing.
As far as bullet release, it takes no more expansion of a neck to release a 30cal bullet than a 17cal bullet. And provided there is any clearance at all, you should not have any pressure issues.
Turning necks thinner would have reduced neck tension and that may have resulted in a better shooting load for you..
But there are plenty of shooters doing well without turning for larger clearances.
If you have excess runout, and jam bullets, you might also benefit from greater clearances.
I don't know, it hasn't been proven.
BoydAllen
Gold $$ Contributor
Mike,
Evidently some very good shooters think that there is more to it than just the minimum required clearance for releasing the bullet without having pressure problems. Fellows that have the credentials, have gone to more than minimum because what they have seen on their targets. Have you seen Jack Neary on YouTube? He is just one example. Don't get me wrong, I have known successful shooters that ran very close neck clearance...but, based on what I have been hearing over this last year, and the shooting I have seen, I am returning my 6PPC necks to produce clearance of .0025, and using a smaller bushing.
Boyd
Evidently some very good shooters think that there is more to it than just the minimum required clearance for releasing the bullet without having pressure problems. Fellows that have the credentials, have gone to more than minimum because what they have seen on their targets. Have you seen Jack Neary on YouTube? He is just one example. Don't get me wrong, I have known successful shooters that ran very close neck clearance...but, based on what I have been hearing over this last year, and the shooting I have seen, I am returning my 6PPC necks to produce clearance of .0025, and using a smaller bushing.
Boyd
I don't believe I've implied that competitors are not doing well enough with large clearances.
Or atleast I didn't mean to do so.
So let's go somewhere else in discussion with this. I'm interested.
Boyd why do YOU believe that larger neck clearances reduce pressure problems in a GOOD way?
This is what I would think:
More blow-by, reducing peak pressures.
A slight change in effective chamber volume.
Less binding from high runout, or existing donuts.
What escapes me at this point, is the benefit of accepting relief of these, rather than addressing them directly. I believe blow-by increases ES (with any less than perfectly matched tension). And I would think competitors would produce straight ammo, and with thickness variance & dounts neck turned away. Effective chamber can be adjusted anytime with throat diameter(if a detrimental peak results from competitive load).
I'm sure you've seen the herd migrate in & out of ridiculous trends. IMO, there is lately a rationalization of shortcuts. Now maybe it's not for me to say, as it doesn't affect me.
But then, who would?
Or atleast I didn't mean to do so.
So let's go somewhere else in discussion with this. I'm interested.
Boyd why do YOU believe that larger neck clearances reduce pressure problems in a GOOD way?
This is what I would think:
More blow-by, reducing peak pressures.
A slight change in effective chamber volume.
Less binding from high runout, or existing donuts.
What escapes me at this point, is the benefit of accepting relief of these, rather than addressing them directly. I believe blow-by increases ES (with any less than perfectly matched tension). And I would think competitors would produce straight ammo, and with thickness variance & dounts neck turned away. Effective chamber can be adjusted anytime with throat diameter(if a detrimental peak results from competitive load).
I'm sure you've seen the herd migrate in & out of ridiculous trends. IMO, there is lately a rationalization of shortcuts. Now maybe it's not for me to say, as it doesn't affect me.
But then, who would?
BoydAllen
Gold $$ Contributor
The word that I hear, from different sources is that they think that more neck clearance gives a "cleaner release" of the bullet from the case neck. As far as fixing problems goes, as far as I am aware, neither I nor the fellows that I am referring to, have a problem to fix. Jack Neary, Tony Boyer, Gary Ocock, and Dennis Thornbury are either in the hall of fame, or hold current world records, or both, and no, I am not trying to put myself in anything even remotely near their skill levels, but I do believe that my ammunition is dimensionally correct, and straighter than the average at a match. Personally, as long as a fellow doesn't hurt himself, I really don't care what neck clearance he runs, it is just that I would not want a reader to come away from this discussion thinking that it is an absolute that less clearance is always better, and that he should not even try something different than .001 to .0015. Some of the recent unlimited aggregate records have been shot with clearances that are closer to .003 than .002., with a 6PPC, and trust me, their is nothing about the fellow's setup that needs fixing or compensating for. We should all live to shoot so well.
I don't like a basis that so & so did it, as it provides little for discussion, much less understanding.
I like
they think more neck clearance gives a "cleaner release" of the bullet from the case neck
That's good stuff, and I wonder if it applies from one finished barrel to another, or one cartridge to another.
If you'd risk, you could test this in the same barrel. Has anyone?
Maybe I can try it in a sense with a 25ppc HBR build, as I get barrels finished in pairs.
But I don't have near access to a skilled barrel finisher for single barrel testing.
I can predict already, that I'd also need to setup for more frequent annealing.
I like
they think more neck clearance gives a "cleaner release" of the bullet from the case neck
That's good stuff, and I wonder if it applies from one finished barrel to another, or one cartridge to another.
If you'd risk, you could test this in the same barrel. Has anyone?
Maybe I can try it in a sense with a 25ppc HBR build, as I get barrels finished in pairs.
But I don't have near access to a skilled barrel finisher for single barrel testing.
I can predict already, that I'd also need to setup for more frequent annealing.
BoydAllen
Gold $$ Contributor
Mike,
Jack Neary spoke quite a bit on this subject on one of the segments on YouTube. The whole thing is based on significant improvement in accuracy at 200 yd. Have you reviewed this material? To my knowledge, short range benchrest shooters do not anneal, primarily (I think) because they do not want to have any reduction in neck tension/bullet pull, based on observed improvements in accuracy with more pull. Virtually none of this is a theory exercise, but is based on the shared experiences of top shooters.
It seems that some shooters are primarily concerned with the case life advantages of tighter neck tolerances. I can assure you that in competition benchrest, accuracy is the primary, if not only criterion. A significant number good shooters throw their brass away after a weekend match. They do this because of the observed difference that it has made. I should add that I am not one of these, and that the reason is that I feel that at my level of shooting, that any advantage from doing so, would mostly get lost in the noise of other deficiencies that are not brass related, such as flag reading errors, and tuning issues.
Boyd
Jack Neary spoke quite a bit on this subject on one of the segments on YouTube. The whole thing is based on significant improvement in accuracy at 200 yd. Have you reviewed this material? To my knowledge, short range benchrest shooters do not anneal, primarily (I think) because they do not want to have any reduction in neck tension/bullet pull, based on observed improvements in accuracy with more pull. Virtually none of this is a theory exercise, but is based on the shared experiences of top shooters.
It seems that some shooters are primarily concerned with the case life advantages of tighter neck tolerances. I can assure you that in competition benchrest, accuracy is the primary, if not only criterion. A significant number good shooters throw their brass away after a weekend match. They do this because of the observed difference that it has made. I should add that I am not one of these, and that the reason is that I feel that at my level of shooting, that any advantage from doing so, would mostly get lost in the noise of other deficiencies that are not brass related, such as flag reading errors, and tuning issues.
Boyd
Personally, I have found 3-4 thou neck tension and 3-4 thou neck clearance noticably more accurate in the 7mm saum.It basically cut my groups in half..It will group in the 0.1s at 109 yards and I have had sub inch groups at 500 yards but most under 1.5 inches(all this of course if I do my part). Prior to this I was running them with 2 thou tension and 1.5 thou clearance.
I shoot Long Range Varmint matches and F-Open---both 600 and 1000 yard matches from local matches to the SW Nationals (6.5 Creedmoor for Long Range Varmint and 600 F-Open/,284 Winchester for the 1000 yard F-Open). I am currently going through the pros and cons of bare minimum clearances to maybe 2 or 3 thousandths and maybe going to full length re-sizing as opposed to my current neck size only routine. It seems to me that, for my kind of shooting, if there is no difference or VERY LITTLE difference between the group sizes when using either of those techniques after developing loads my rifles like, then the next question is brass life---How many reloads can I get on them (I will be annealing at some still-to-be-determined number of reloads). NOW, in my mind, IF all of those factors add up to very little accuracy and/or brass life differences/advantages or disadvantages, then having a neck to chamber clearance on the "looser" side and/or using full length resizing will result in more ease when chambering a round...resulting in NO "SKETCHY" BOLT FORCES required and thus fewer times for me to be concerned about "chamber fit" or maybe even having a piece of fired brass stick during a timed event. I'm thinking that the "warm fuzzy" that having my rounds go in and out of the gun with NO cause for niggling worries just may be worth more to me than any TINY gains or losses in the other areas would be-------At least I'll shoot with a more relaxed approach and, for me, THAT always results in me shooting better!!!
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