Neck turning questions

[ATH]

I've ordered a Shilen Savage 243AI barrel with .270" neck, the largest they offer. Apparently this is a "may or may not need to neck turn" diameter.

My question is, how do you need to know if you need to neck turn? I've only worked with standard chambers before so this has never been an issue.

I have a couple hundred Lapua 243Win brass waiting on the rifle. I'd planned on loading up fireforming loads after I got the barrel headspaced and shooting them. Now I'm wondering how I know whether I need to neck turn them or not.

 

[bigngreen]

Load a bullet in a case and measure it, you'll want to be .003+ under what you measure

 

[ATH]

So for a .270" neck chamber a loaded round should measure .267" or less? Easy enough, thanks.

 

[AZShooter]

Based on the thickness of Lapua brass, I would bet you will be turning your necks. Here is a good article to read on the details of neck turning: Neck Turning Basics

I would consider the .003" difference as the minimal clearance you would want. That is only .0015" neck clearance per side! I tried to find some data on what others are using and so far haven't found much.

I have a 6mm-284 reamer for no turn with Lapua 6.5-284 brass necked down. The reamer neck is .277" The neck clearance is .004" I use a .272 bushing for a .001" neck tension. This has worked out well in three rifles which are repeaters and used for hunting.



Once you have your necks turned you will have to use a bushing die (or a custom die) to achieve the neck tension you want. I would suggest using a bushing that reduces the OD of the neck by .001" and .002".

Good article on the 243 AI 243 Win Cartridge Guide within AccurateShooter.com

 

[ATH]

Thanks for the links. I had hoped to avoid the cost and learning curve of introducing myself to bushing dies but perhaps it is inevitable at this point.

 

[AZShooter]

There is a learning curve to turning necks that is more challenging than running a piece of brass up into a S bushing die.

While some will suggest otherwise, I find that it is easier to have a S bushing die and a body bump sizer die rather than a FL/ S bushing die. The serious handloader will also get a competition seating die. Here is the set:

Redding Type S Match Bushing 3-Die Neck Sizer Set 243 Winchester

 

[ATH]

Based on the thickness of Lapua brass, I would bet you will be turning your necks. Here is a good article to read on the details of neck turning: Neck Turning Basics

I would consider the .003" difference as the minimal clearance you would want. That is only .0015" neck clearance per side! I tried to find some data on what others are using and so far haven't found much.
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Read the link. The one question this raises for me is when to neck turn with regards to forming AI cases. If I neck turn the virgin 243Win cases, when I fireform them I would think the location of the neck -- and how much of it is therefore turned -- would change somewhat -- when the shoulder blows out. It would seem some of the turned portion would end up on the shoulder. But if the brass is too thick I won't be able to fireform them to start with.

Thoughts? Lapua brass is expensive -- I want to get it right.

MTA: Found a post by JE Custom which touches on this -- turn first and just stay off the shoulder a tad to avoid messing up headspacing upon fire forming.

 

[dkhunt14]

I turn my 6 BR brass for a Dasher almost all the way to the shoulder. When fireformed the turned part goes to the middle of the shoulder. That way you have a neck that is turned all the way past the shoulder body junction and no chance of a doughnut. When I fireform I keep the bullet jammed so it helps hold the case against the boltface. I also have done this by making a false shoulder and keeping the bullet jammed. The false shoulder is made by running a .257 neck turning expander in the case after it is turned. Then you back your bushing off and keep screwing it down till you get a crush fit. That helps hold the case against the bolt face. I also keep the bullet jammed so it raises pressure and also help hold the case against the bolt face. Matt

 

[AZShooter]

I found the same thing in several articles, don't turn go all the way to the shoulder, fireform, then turn up to new shoulder if necessary.

I turned the K and M turner into the shoulder when I made my 30BR/308. The 30 BR reamer was plunged deeper to headspace as a 308. I used Lapua brass and had to turn the necks down to .0105". The shoulder angle went from 20 degrees to 30 degrees. To date I have had no issues with the cases after 7 firings. The necks are thinner than what you will have but shoulder angle only increased by 10 degrees while yours will increase by 20 degrees. I would think you will have sufficient brass thickness in the necks to cut into shoulder (slightly) before fireforming.

I found this thread Dano says not to cut into the shoulder too far...

Dano1 one of our LRH posters says this:

"The key for turning it prior to fireforming it to not cut into the shoulder too far as to mess up your head spacing.... All Ackley improved design cases headspace off of this point while fireforming, so leaving enough is important as excessive headspacing will mess up the shoulder, cause casehead separations and other problems.....to find this point, turn the necks until the cutter slightly cuts into the shoulder, check the case in the the chamber and makesure it will still chamber with some slight resistance as it is crush fitting and headspacing. "

I then load and fireform and after resizing and cleaning, I check to see if I need to clean up the neck further, as the expander ball seems to push out any doughnut, this takes care of the problem for me."

link: http://www.longrangehunting.com/forums/f28/turn-necks-before-fire-forming-ackley-improved-74824/

I suppose if in doubt prep 20 cases and use them for a dozen firings to see if you have issues.

 

[ATH]

Thanks for your replies, gents. Not only do I fully understand the process now but know exactly which tools I want to get for the job. You have been a big help.

 

[dkhunt14]

If there isn't enough of a step in the turned brass it will drive the case in the chamber when you fireform. That is why I turn to neck shoulder junction and use a false shoulder to headspace. A neck turner can not turn to a perfect thickness where you stop at and if you go past there like in a Dasher or Ackley IMP and expand up and size enough of the neck to headspace you get the best of both. Keep a crush fit when shutting the bolt and the bullet in the rifling and you get perfect cases with no donut or case stretching. This is the way most benchrest and accuracy guys do it. Matt

 

[dkhunt14]

You want a minimum of .003 clearance. For hunting guns I sometimes use .004 for added safety. If you turn the necks to .012 it will give you .003 clearance or a loaded round of .267. If you turn them to .0115 it will give you .004 clearance or a loaded round of .266. Matt