Reamer or Chamber Neck Diameter Question

[Henryrifle]

Is there a ratio of loaded-round neck diameter to reamer neck diameter that optimal for accuracy, chamber sealing and brass longevity? If annealing makes a difference, I anneal after every firing.

For my straight .284 with a .316 diameter neck, brass turned down to .012 (.308 loaded round diameter - .008 clearance 97.5%) to .0135 (.311 loaded round diameter - .005 clearance 98.5%) seems to shoot equally well with approximately a .002 interference fit. I have not tried any other neck turned thicknesses.

Does the case neck begin the chamber sealing process or is the neck the last part of the brass to seal? Does that matter?

I have ordered a 7-6.5 PRC reamer with a .315 neck but thinking about changing to a .314 or .313. I am not sure why but it seems easier to consistently turn Lapua brass to .012. In a .313 chamber that would be 98.4%.

Is all of the above irrelevant?

Thanks,
Hank

 

[TaperPin]

Since you turn necks, it might be fun to have a tighter reamer made so you can test different clearances in your rifle. I had a .315” that shot better than needed for the purpose, but now I’m getting slightly tighter reamers to have the option for more or less clearance.

I look foreward to the team No-Turn-Neck vs team Turn-Neck discussions to come shortly.

 

[memilanuk]

The vast majority of my shooting has been 308 Winchester, and a lot of that in the FTR discipline - which borrowed a *lot* from Palma / TR (for better or worse), and still hangs onto it today. Which is to say, *very* generous neck clearances. My 'match' chamber (2013-2017 US FTR team reamer) has a neck diameter of 0.343, and loaded ammo generally runs 0.335-336". That's been a pretty successful combination, in that specific context, but there are some artificial constraints (rules/organizations) that drive that, and limit the use of tighter necks for the venue.

Bruce Teel has some interesting content on neck clearance on his YT channel... but the TL;DR version is to set aside some cases early on and test, for yourself, with your components, in your barrel, what amount of neck clearance shoots best for you.

I'm a tad bit skeptical, personally, for a number of reasons - but I don't run in the same crowd as Bruce does (multiple time LRBR national champion) so you should probably watch the videos and decide for yourself.

 

[J_idaho]

I’m not a machinist but this is a subject that has peaked my interest for awhile. There are a few different options on this. But I started watching Bruce Teels YouTube videos recommended from witch doctor Bryan zolnikov. He really spills the beans about his
Method during his interview with Erik Cortina there isn’t a one simple answer as it’s all about finding what works for your rifle and brass. Here is a link to the interview.

https://youtube.com/@bruceteel7?si=TtkMQ4qywko-c2Ro

 

[Infrequent Shooter]

I’m not a machinist but this is a subject that has peaked my interest for awhile. There are a few different options on this. But I started watching Bruce Teels YouTube videos recommended from witch doctor Bryan zolnikov. He really spills the beans about his
Method during his interview with Erik Cortina there isn’t a one simple answer as it’s all about finding what works for your rifle and brass. Here is a link to the interview.

https://youtube.com/@bruceteel7?si=TtkMQ4qywko-c2Ro

What is the gentleman Ted's last name. I will have to study him for sure!

 

[J_idaho]

What is the gentleman Ted's last name. I will have to study him for sure!

There’s a link at bottom to his page. Bruce Teel. https://youtube.com/@bruceteel7?si=TtkMQ4qywko-c2Ro

Maybe you meant to reply to someone else’s post.

 

[Infrequent Shooter]

There’s a link at bottom to his page. Bruce Teel. https://youtube.com/@bruceteel7?si=TtkMQ4qywko-c2Ro

Maybe you meant to reply to someone else’s post.

Ted Larsen is the man's name I was looking for. Thanks.

 

[Henryrifle]

Several interesting replies above--thank you. Some of them are are about adapting to rules or known 'good' reamers and turning/loading combinations.

It seems that Bruce is testing different amounts of neck turning for accuracy - but for a reamer that was someone else's design.

Maybe there is some secret sauce in the ratio of neck diameter to loaded round diameter -- maybe it's area rather than diameter. Maybe there is nothing there at all and Bruce has the right answer, find someone with a 'good' reamer and test all aspects, one at a time, to achieve the accuracy you need/want.

Without living on a range, testing is pretty hard...

I am still curious about case sealing. When does the neck seal and is there an amount of neck clearance that seals the chamber better, faster or more consistently than others. I am sure that has a relationship to neck thickness as well...

Thank you all,
Hank

 

[memilanuk]

It seems that Bruce is testing different amounts of neck turning for accuracy - but for a reamer that was someone else's design.

Pretty sure he's got his own secret sauce reamer design(s), if you listen to the end of the interview with Cortina.

 

[Alex Wheeler]

Its hard to test clearance and keep neck tension the same. From all of my experience I can say, all you need is enough clearance. More wont really hurt, less will.

 

[TaperPin]

When does the neck seal and is there an amount of neck clearance that seals the chamber better, faster or more consistently than others. I am sure that has a relationship to neck thickness as well...

You’ll read some very accomplished shooters say the less clearance and thinner the neck walls, the faster and better things seal. That sounds logical since the thinner the brass the less pressure it would take to expand, and the smaller the clearance the less of a gap to span.

Better?

If low neck tension shoots better, it might be better.

The other camp of equally accomplished shooters will say minimal neck thickness, isn’t always the best choice, and there are many examples of loads that shoot better with the extra neck tension of thicker necks.

It will also be argued that minimal neck clearance may not be as important if a bullet is stabilized by the rifling as the neck expands to no longer touch the base of the bullet.

Hopefully I summarized that correctly.

One thing everyone can agree on is the importance of testing loads for a specific barrel, to see what shoots best.

 

[Alex Wheeler]

I would not worry about the neck sealing. Unless your getting gas in your face, the cartridge is sealing and 100% of the gas energy is being used to push the bullet. Theres only so much volume inside the barrel. So long as no gas is leaving through the chamber end, there is no waste of energy.