Here is a question that has plauged me for some time. With a given that for this discussion any result will be in a chamber with a release clearance apropriate to the purpose of the intended use of the cartridge.

The question relates to possible changes in case to case in neck tension due to minute differences in springback. It is a given that necks are turned in all cases.

Would the neck wall thickness be better in the .010 - .012 or in the .014 - .015 or right up to .017 - .018.

The reason I ask is that a friend had a chamber reamer made to give him a 1.5 thou RC (release clearance) with a neck wall thickness of .010 in his 20 VTT

I have my 20 VT with a similar RC and neck wall thickness of .014

On the other hand for my 7x57 I have some brass with a turned neck wall thickness of .0175 and again with a RC of .015.

All three samples have been built for accuracy.

So the question is which neck wall thickness will give the most uniform neck tension and release.

May not be important for anything other than my understanding of brass properties.

TIA

Von Gruff.

You might be better off asking that question over on www.benchrest.com - those guys are into neck turning big time... But since you asked here, hey, I'll have a go.

I don't believe there is a straight answer to your question, in the sense that there is a clear connection between neck wall dimension and consistency of neck tension. (Note, I don't think anybody has ever seen or even measured a "live" neck release, so all we can strive for is consistency in neck tension during seating).

In days past, it used to be quite common for benchresters to turn their Lapua .220 Russ necks quite a bit to produce their PPC cases. But, if you check recent discussions on forums like benchrest.com, you'll see that more and more people are having reamers made, which allow them to simply clean up necks - i.e. uniform as opposed to specifically reduce neck wall dimensions. Don't ask why this shift has taken place, maybe the Lapua brass used these days is more uniform, or maybe orginal PPC reamers were made for brass such as Sako or Norma, which has thinner neck walls?

It may be entirely possible that one benchrester or the next prefers a particular neck wall thickness. That would be par for the course in shooting and reloading - more ways than one to skin a cat...

Consistent neck tension is influenced by at least the following factors: neck wall uniformity, brass hardening (anneal to uniform), and die used to size. I don't think neck wall thickness in itself is an indication of consistency of neck tension.

There is pretty good evidence, though, that brass loaded and left for comparatively short periods of time (days, weeks?), will experience changing neck tension due to changes in the loaded brass necks. I believe this phenomenon is documented over on www.6mmbr.com.

- mike

mho has covered it well. Here is a link you might find of interest. http://benchrest.com/showthrea...336-BR-neck-diameter

Thanks guys. That fairly well sums up how I felt about the question. Have looked at both sites on ocasion but not investagatively.
The link to the specific neck wall thickness discussian was excellent 243winxb.

Von Gruff.

For factory chambers, I use .0145 neck thickness. That works with standard resizing dies.
For tight neck chambers, you just have to work the numbers relative to the chamber neck ID.

I think the question is more academic than anything else except that neck tension is always at the forefront in benchrest/competition circles.

I think it is moot as far as any other shooting is concerned...in that there are MANY neck tensions that work and as long as the tension is relatively uniform you will get the accuracy you want/need.

Reading about all the different neck sizes used in winning rifles, turn vs no turn necks, brands of brass, etc, gives you a small idea how nebulous the question is.

Neck thickness related to neck tension and it's import has been proven time and time again, but WHAT amount of tension gets into the proverbial bucket of worms.

There are a ton of OTHER more important accuracy affecting factors that are more important.

It would take a lot of work and a sophisticated strain guage tool and TONS of ammo and shooting to actually determine a specific neck tension and I'm thinking it would be specific to ONE lot of a specific brand and maybe ONE specific cartridge in ONE specific rifle...and maybe for only ONE firing/reloading cycle.

I'm definitely not one for that kind of brutality to myself.

Definitely could get into the realm of esotericism...big time.

Luck

quote:

Originally posted by FOOBAR:
I think the question is more academic than anything else except that neck tension is always at the forefront in benchrest/competition circles.

It was an acedemic question bought on by my friend getting his reamer mader for a .010 turned neck and having to turn so much of the cases when I only had a .005 clean up on mine. I just wondered if there was a reason for the thinner neck wall ( other than his GS recomended it) and if there was a difference in results. I dont do benchrest although have read a little of the brass prep techniques to help with my "varmint rifle" build.
I have my Wilson straight line dies and various suitable bushes to suit so the standard chamber reference is moot.
Again the link provided by 243winxb is clear in that there seems to be a drift away from excessive neck turning because it offers no advantage over simple clean up of good quality brass.
http://benchrest.com/showthrea...336-BR-neck-diameter

Von Gruff.