Neck turning - question on tolerances

[Simon C]

Hi all,

I have just neck turned (skim clean up) a heap of fireformed lapua brass for my dasher. What a joy

The chamber is a 272 neck 'no turn' according to the reamer and was recommended by PTG.

They were all run thru my sinclair expander mandrel (6mm) prior to turning. Checking them on the dial indicator, they were running anywhere from .013"-.015"

There were a bunch that flatlined at .014" so I made the decision to set the cutter to turn .014".

The primary question is: Given that there were also a bunch that varied .013-.014", should I look to go in to .013" and re-turn the lot or leave em as they are?

I'm not sure how much you can clean up the necks on the no turn chamber. I'm interested to hear how others approach neck turning for no turn or tight neck chambers.

Cheers,

[Dazza]

Hi all,

I have just neck turned (skim clean up) a heap of fireformed lapua brass for my dasher. What a joy

The chamber is a 272 neck 'no turn' according to the reamer and was recommended by PTG.

They were all run thru my sinclair expander mandrel (6mm) prior to turning. Checking them on the dial indicator, they were running anywhere from .013"-.015"

There were a bunch that flatlined at .014" so I made the decision to set the cutter to turn .014".

The primary question is: Given that there were also a bunch that varied .013-.014", should I look to go in to .013" and re-turn the lot or leave em as they are?

I'm not sure how much you can clean up the necks on the no turn chamber. I'm interested to hear how others approach neck turning for no turn or tight neck chambers.

Cheers,

G'day Simon,

With a 0.272" neck chamber, I wouldn't bother turning the necks, you're just increasing the amount of clearance between the loaded round and the chamber. Which means you'll be overworking the necks when you resize the fired rounds............

You would be better off sorting your brass to find the most concentric necks, and using these as your match cases. You can use the others for practice(then compare your scores ie: concentric vs non concentic)

I'm assuming you're using Lapua 6BR brass? If so, you might need to buy a few boxes to get enough match rounds . The concentricity of the necks isn't as good as everyone makes out, although a lot better than Lapua 6.5/47 brass which has lousy neck concentricity...........

If you really want to neck turn, I'd suggest getting your reamer reground to a 0.268" neck and re-chambering your barrell, probably something you didn't want to hear .

Then you could turn the necks to 0.267" with you bullet of choice seated. That way you would get 100% clean up and 0.001" clearance of your loaded rounds. I'm thinking of getting a PTG reamer in 6/6.5x47L but with a 0.267" neck to get 100% cleanup on most cases

If you'd like anymore info, send a PM.

Regards,

Darren

[Simon C]

THanks Darren,

I only skimmed them to 0.014" as this was the most prevalent wall thickness I encountered with the odd high or low spot (0.013-0.015").

I spoke to somewone else today, who also indicated that I should probably batch the brass into 2 groups - i.e the 0.014" flatliners in one group and the 0.013-0.14" in the other.

I have about another hundred to fireform

[ned kelly]

G'day Simon,
I concur with Dazza, however he missed one point (probably deliberately too! ) that we've discussed at length.

The reamer is a 0.272" neck, the barrel may well be stamped a 0.272" neck but if you can remove the barrel and measure the actual neck internal diameter, you will find it up to another thou bigger; i.e. 0.273"

So if you clean up all your necks to 0.013", a loaded round will measure 0.269" in most likely a 0.273" chamber. I prefer a max of 0.003" clearance and ideally being able to turn for 0.002" clearance which would be a 13.5 to 14 thou neck thickness for a 0.273" chamber

hope this helps

Cheerio Ned

[AlanF]

Ned,

I have never been convinced that very tight neck clearances are worthwhile. Supposedly the reason is that necks are worked less and therefore will last longer and retain their elasticity longer. I ran about 0.007" clearance in my first 6.5 barrel and don't remember a single neck failure in about 7 to 8 firings. And if the properties of the brass are of concern, then annealing is an option (but I admit I've never done it). On one occasion when I was running 0.002" to 0.003" clearance I had some powder fouling in the neck of the chamber which made chambering difficult and seemed to affect accuracy - I say this because I cleaned the chamber neck with a bronze brush mid-shoot and the problem went away. I have read that this sort of interference with the neck can cause extreme pressures and safety concerns. So that is why I opt for about 0.004" minimum clearance. I think you will find there is a good proportion of the US BR population who agree with me, particularly those shooting the bigger calibres.

Alan

[Simon C]

Thanks guys.

I have them running between 0.013-14" so I should not run into the issue you had Alan. With this thickness, the cleanups were <50% on all cases...most were actually more like 33%.

I also went into the shoulder a little to combat the potential for donuts....I've never experienced them before but have read a fair bit about them. Are they more prevalent in any particular chambering? I can see how the would form with a neck turned case but do they also form on un-turned brass?

[ned kelly]

G'day Alan,
no worries, it hasn't hurt your performance, so maybe we're on the wrong track, but it does make me think of more than a few recognised BR shooters who came along to F class and made a statement with their shooting, equipment and thinking.

BTW I do not put myself in that category.

So it would be nice to know how many shooters actually neck turn and the clearances they run in their chambers and whether they find it worth the effort and improvement, if any, in accuracy.

I know in my 6ppc, I'll get 20 cases through 3000+ rounds in a barrel with a 2 thou clearance (150+ firing/sizing cycles) and I've had probably 2-3 fail in 14 years of BR and certainly no pressure issues in a 100+ rounds per day of shooting. God only knows how many thousand of rounds over the last 14 years. And further more, I've never had a failure caused from overworking/firing the brass at the "normally" high BR level chamber pressures.

However, I'll never forget the some of the comments from the gathered shooters about Dazza's pop gun 6ppc and 70gn sierra match kings at Castlemaine 3/5/600 some years back and the surprise that he actually placed 2nd in open against some fancier shooters and more "appropiate" calibres............

As an observer it cracked me up and convinced me to have a go at F open!

If a shooter thinks neck turning will help, it probably will...........

It would be a boring sport if we were all the same.

Cheerio Ned

[RAVEN]

On one occasion when I was running 0.002" to 0.003" clearance I had some powder fouling in the neck of the chamber which made chambering difficult and seemed to affect accuracy [/quote]


Interesting Alan
I have 6X47 chambering from someone I won’t mention
My fired cases have allot of carbon burning all the way down the neck and part way up the shoulder.
I have never been happy with this and I wonder if this is the cause of the erratic grouping for this barrel and chambering combo.

I have also had 115berger Amax and Lapua projys not make it to the target. And now given up on it I will rechamber this barrel with my own reamer and see how it goes.

Simon my preference is for 100% turned necks then you know you have consistent neck wall thickness.
I usually run about .004" clearance.
Cheers
RB

[Steve 2141]

For me the whole reason for neck turning is to eliminate another possible variance, that being consistent neck tension, for those who haven’t shot Benchrest, you would quite amazed by how much as little as 0.001” change in your neck bushing can change a unproductive load into a goer. I run 0.0015” clearance which gives me good brass life on an Improved 6BR pushing 105gr VLD Bergers at 3050ft sec and don’t have a problem with excessive carbon fouling on the necks of the brass.

If you are going to run a no turn neck chamber and not turn your brass you might be best served to use a standard die, although you have no control over the amount of neck tension the variance will be minute across your batch of brass especially after several firings as these dies work the brass more.

The only problem with running close tolerances is the environment you’re shooting in, the smaller the gap the cleaner you have to be.

[AlanF]

For me the whole reason for neck turning is to eliminate another possible variance, that being consistent neck tension...

Steve,

I agree that is the main reason why we neck turn - my comments were based on that being a given. I think you can still get even neck tension while having plenty (within reason) of clearance, and avoid the pitfalls mentioned above.

However I don't claim to be an expert - in F-Open we don't need to do things quite as meticulously as the BR crowd.

Alan

[Steve 2141]

RAVEN

Did you get my PM, I sent it on Saturday.

Cheers

[RAVEN]

Yep Thanx Steve