Neck clearance effect on ES and SD

[lawrence97]

Just wondering if the clearance between chamber and neck affects ES and SD. I have a .313 necked 284 win. And based on recommendations of using .004-.006 clearance I went with .005 (loaded round of .308) for my first 100 pieces of brass but after finding a good shooting load and seating depth, I was unable to get below 20 fps of ES for 8-10 rounds under a match condition firing sequence.

For my next batch of brass I turned the necks for a .003 clearance (loaded round of .310) and initial testing is giving me 7-15 fps of ES. Same powder charges with less clearance are a little faster but I will play with charges to get velocity equal. Groups are tighter at 1000 due to reduced ES although it wasn't terrible.

Are there any issues with running .003 or any surprises I may run into which I need to worry about?

Forgot to mention but all testing has been with .001-.002 tension and no noticeable difference between one neck tension or the other.
Thanks.

 

[Lapua40X]

I have been running .003 with my 6BR and haven't had any issues.

 

[KT]

How many rounds do you have down the barrel?

 

[Terry]

I have a .284 Shehane with a .313 chamber and .310 loaded rounds, no problems.

 

[CatShooter]

At first, I ran my tight neck 6mmBR with 0.00075" (3/4 of a thou) total neck clearance - it was a spoiled princess to live with.

I re-cut the case necks to a total clearance of 2.75 thou and it is a joy to own.

 

[lpreddick]

CatShooter: a very large number of us are using the pt&g .2704 6mmBR reamer that leaves the .00075 clearance and my gun, for sure, shoots selected bullets and powder into very small holes. why would yours not shoots the same? my friend's 6mmBR,having .0015 clearance, shoots small holes as well. i was under the impression that minimum clearance contributed to accuracy. perhaps the 6mmBR, and it's clones, are so good that clearance is not critical...what about ED and SD in close vs not so close clearance?

 

[CatShooter]

CatShooter: a very large number of us are using the pt&g .2704 6mmBR reamer that leaves the .00075 clearance and my gun, for sure, shoots selected bullets and powder into very small holes. why would yours not shoots the same? my friend's 6mmBR,having .0015 clearance, shoots small holes as well. i was under the impression that minimum clearance contributed to accuracy. perhaps the 6mmBR, and it's clones, are so good that clearance is not critical...what about ED and SD in close vs not so close clearance?

I have had this gun for a while - it has a 0.262" neck. It shot well, but the slightest bit of dirt (ash) in the neck, and groups went down the tube. I spent more time cleaning it than I did shooting it.

I watched a video by Jack Nealey and he mentioned that he was running a very tight neck and had problems with it, and he cut cases for a 3 thou total clearance and it was fixed. His problems were just like my problems, so I cut my cases again, and "Badda bing, badda boom" the gun behaved like it was on rails.

 

[lawrence97]

KT, I have 315 rounds down the tube. The last 30 rounds out of it were with .003 clearance and ES dropped in half compared to my results with .005. ES used to be 20-26 and now 7-15 but I still need to rework a load for cooler weather!

 

[kyreloader]

I have a .284 Shehane with a .313 chamber and .310 loaded rounds, no problems.

I shoot the same without incidence.

 

[jsthntn247]

Does case size (powder amount) influence how much clearance you need? Ie. bigger cases need more neck clearance because they burn more powder?

 

[CatShooter]

Does case size (powder amount) influence how much clearance you need? Ie. bigger cases need more neck clearance because they burn more powder?

No... the clearance is to make sure that there is no hindrance to the bullet leaving, and enough clearance is needed to allow some ash/dirt to get in the neck and not interfere with the bullet release - anything more than that is not needed.