Proper Neck Clearance For a .284

[JBO]

I have a couple question and I hope I can get some help here. I have a .284 with a .313 neck.
I've been told I should have a minimum .005 neck clearance with a .284 . My loaded rounds are from .3095 to .308.
When seating bullets my neck tensions do vary. Measuring the walls after turning I'm between .0125 to slightly under.012.
How much clearance is too much before it becomes detrimental to accuracy? What issues will not enough clearance cause?
What accuracy issues will varying seating pressures cause and what should be the SD?
I do use a seating gauge and I'm experiencing on the high end 10 lb variances. I realize many of my dropped shots are just my inexperience but I want my loading process is correct... appreciate any help.
JBO
I also anneal.

 

[ShootDots]

I am sure you could get away with 3K neck clearance. However, for whatever reason, it appears that the 7mm's prefer a bit more. I know 4K works well (that's what I use) and there is nothing wrong with up to even 7K clearance, except you are really working the brass more than needed.. TOO little of clearance is worse than "slightly more than necessary"..

 

[lawrence97]

I have a 284 with .313 neck and I run a .013 neck wall thickness and a .310 loaded round. I have not had any clearance issues and I believe it's best to start with your brass turned for minimum clearance and test it because if you shave it all to have .005 there is no way to gain back what you shaved. Turn necks for .003 and just a handful at .005 so you can compare. Let the rifle decide what it likes. I shoot fclass and I do not clean until the end of the day after a match and I have not had any clearance issues running a .003 clearance.

 

[JBO]

I am sure you could get away with 3K neck clearance. However, for whatever reason, it appears that the 7mm's prefer a bit more. I know 4K works well (that's what I use) and there is nothing wrong with up to even 7K clearance, except you are really working the brass more than needed.. TOO little of clearance is worse than "slightly more than necessary"..

I have had many shooters agree with you regarding the .284 needing more neck clearance, Eric Cortina suggested minimum .005 I was just wondering what detriment to accuracy it causes running less.

 

[JBO]

I have a 284 with .313 neck and I run a .013 neck wall thickness and a .310 loaded round. I have not had any clearance issues and I believe it's best to start with your brass turned for minimum clearance and test it because if you shave it all to have .005 there is no way to gain back what you shaved. Turn necks for .003 and just a handful at .005 so you can compare. Let the rifle decide what it likes. I shoot fclass and I do not clean until the end of the day after a match and I have not had any clearance issues running a .003 clearance.

Thanks Lawrence, I'm not worry about cleaning issue it's more an accuracy issue having more neck clearance. I also ran .003 for awhile but was advised many shooters recut my necks down for additional clearance.

 

[lawrence97]

Are you having issues with .003 clearance?

My rifle shot better with the tighter clearance although I did test what others recommended (.004-.005). I noticed better ES and SD with tighter clearance.

If you already have some brass shaved to .003, sacrifice a few and shave them to .005 to compare!

Have fun and test/compare for yourself.

 

[dragman]

I have ran all my .284's between 3-6 thousandth's clearance. I too agree a couple thousandths extra probably wont be noticed but too tight they can get real problematic

 

[Steve Blair]

My loaded Shehane rounds are ~Ø.3085" neck in a Ø.313" chamber for ~.0045" diametral clearance. A little either way is unlikely to make a difference as long as it is not too tight.

 

[TonyR]

In my experience, the uniformity of neck clearance, meaning neck wall thickness, is more important than the clearance itself. I believe that is because uniform neck tension is extremely important. I have shot everything from 0.0015 to 0.0050 inches and I couldn't see any difference under match conditions as long as they were all vey close to the same. I recently did a test at 300 yards with a large number of cases firing the same tuned load with one shot each at a target spot. That way I was able to measure the vertical from point of aim for each case. Somehow two cases with a loaded neck of 0.309 slipped into the set which was otherwise 0.310 and the statistics program picked them out right away meaning that they were outliers to such a degree that it made loaded neck diameter a statistically significant variable. Everything else I measured was considered random noise by the program. So if your neck walls are between 0.0120 and 0.0125, some of your loaded rounds will probably differ by 0.001 and I believe that will cost you vertical points.

 

[Laurie]

I believe that is because uniform neck tension is extremely important.

An interesting point, Tony. I wonder if the .284 is unusually sensitive in this respect? Your conclusions tie in with an article written by one of our GB league F/O shooters maybe 18 months back on experiences with a Bench Source annealing machine. He moved to annealing after every firing and was adamant that this (the resulting reduction in neck tension inconsistencies) improved his 'elevations' noticeably. I'm pretty sure his cartridge was either 284 or 284 Shehane, not 7mmWSM.

 

[TonyR]

I believe that is because uniform neck tension is extremely important.

An interesting point, Tony. I wonder if the .284 is unusually sensitive in this respect? Your conclusions tie in with an article written by one of our GB league F/O shooters maybe 18 months back on experiences with a Bench Source annealing machine. He moved to annealing after every firing and was adamant that this (the resulting reduction in neck tension inconsistencies) improved his 'elevations' noticeably. I'm pretty sure his cartridge was either 284 or 284 Shehane, not 7mmWSM.

I do the same thing with a BenchSource on all of my brass for that reason. I haven't noticed the Shehane being any more or less sensitive to this than my ShortMags; but there is nothing scientific to back that up. There was recently an extensive discussion here about the use of arbor presses with force measurement gauges to pick out cases with inconsistent neck tension. Since the OP seems to have something that measures seating force, he might find that thread interesting.
http://forum.accurateshooter.com/index.php?topic=3830355.0

 

[JBO]

In my experience, the uniformity of neck clearance, meaning neck wall thickness, is more important than the clearance itself. I believe that is because uniform neck tension is extremely important. I have shot everything from 0.0015 to 0.0050 inches and I couldn't see any difference under match conditions as long as they were all very close to the same. I recently did a test at 300 yards with a large number of cases firing the same tuned load with one shot each at a target spot. That way I was able to measure the vertical from point of aim for each case. Somehow two cases with a loaded neck of 0.309 slipped into the set which was otherwise 0.310 and the statistics program picked them out right away meaning that they were outliers to such a degree that it made loaded neck diameter a statistically significant variable. Everything else I measured was considered random noise by the program. So if your neck walls are between 0.0120 and 0.0125, some of your loaded rounds will probably differ by 0.001 and I believe that will cost you vertical points.

Thanks Tony, Being new to the sport and getting advice from experienced shooters helps the learning curve. I know before the three minute prep time I'm dropping shots. Everyone really is great in passing on their experience and knowledge.

 

[JBO]

I believe that is because uniform neck tension is extremely important.

An interesting point, Tony. I wonder if the .284 is unusually sensitive in this respect? Your conclusions tie in with an article written by one of our GB league F/O shooters maybe 18 months back on experiences with a Bench Source annealing machine. He moved to annealing after every firing and was adamant that this (the resulting reduction in neck tension inconsistencies) improved his 'elevations' noticeably. I'm pretty sure his cartridge was either 284 or 284 Shehane, not 7mmWSM.

Thanks Laurie