Neck turning tool & Advice please

What you want to do is fine.

Many folks use standard SAAMI chambers with .344 to .345 inch chamber necks and shoot thin walled match cases with .012 inch or less neck wall thickness. Their test groups are often better than benchrest records with super tight necked chambers.

Note that for rimless bottleneck cases, the bullet and case neck are aligned to the bore by the case shoulder mating with the chamber shoulder very hard when the firing pin strikes the primer. It doesn't matter how much neck clearance there is. As long as the case neck's axis is aligned with the case body axis, the bullet will be very well aligned with the bore when the round fires. If the case neck's a bit misaligned with the case, the bullet's going to be misaligned with the bore when its fired.

Same thing happens with either full length or neck only sized cases; they both fit the chamber virtually the same when fired. Full length sized ones are often times more centered at their shoulders when chambered than neck only sized ones.

 

Bart, you're makin it sound like anything will work just fine.
But it just isn't so easy..

(343-308)/2 = 17.5thou thickness
I highly doubt 308 brass is even running that thick, so turning here would be only to eliminate variance
(not for clearance).
Also, you do not want to over-size necks. Anything from .0005(fitted) to .003"(total) is plenty of clearance, and keeps sizing requirements rational.

Crank, go Sinclair for turning equipment. It's the best 'system' IMO, including cutters, sizing mandrels, and neck mic, -from one very good source.
This is what you need:
Micrometers - Sinclair Digital Case Neck Micrometer
Neck Turning Tools - Sinclair Premium Neck Turning Kit
Case Prep Units - Sinclair Power Center
Case Prep Units - Sinclair Case Drive and Holder Combo
And go ahead & throw this in the order:
Concentricity Gauges - Sinclair Concentricity Gage with dial indicator
And these:
Bullet Comparators - Sinclair Bullet Comparator #1
Calipers - Large Display Digital Caliper
Well that should get you started. I know of no other source with such a complete system.

As far as all other clearances, the same holds as with necks. You don't want to be oversizing ANYHING. In contrast, there is nothing wrong with tight clearances.

To throw in an extreme example, my 6.5wssm has -no more than- .0005" clearance anywhere, right from the git go. So my brass with over 20 reloads still measures exactly the same as first fireformed to. I did not even touch the brass with a die until it's 8th reload!
NO PROBLEMS
And that doesn't happen by chance

Well, your pickin your reamer. So make it just as you wish it to be.

 

Mikecr, I've full length sized .308 cases in a standard RCBS die with its neck lapped out to a couple thousandths smaller than loaded round's neck diameter. Got 50 or more reloads per case from SAAMI chambered match rifles and never annealed a case neck. Ammo's shot 1/2 MOA or better at 600 and 800 yards. All with case necks unturned having a wall thickness spread of a thousandth measuring .336 loaded round neck diameter in chamber necks at .345 inch.

Others have done the same thing and as I have and we've shot 20-shot test groups at 600 and 800 yards smaller than benchrest records. Sierra Bullets' been doing this since the 1950's and their 30 caliber match bullets' 10-shot test groups would go into the ones at a hundred yards.

It ain't hard to do if you know all that's needed then you don't need to waste time or money with anything more.

 

Crank, capacity is the final factor in culling brass. But this check is best performed on unsized -straight from the chamber- fully fireformed brass. This, because it's the only time the brass is actually the same size (externally).
Otherwise, (after FL sizing) your not qualifying the brass on it's own virtue. You're mixing in factors like annealing, and case lube consistancy, that can lead to capacity variance which is not a brass issue.
And don't qualify with brass weighing, as this may not correlate to capacity(unless it's leaves the pack in an extreme).

I've had several 'concentricity' gages for comparison, and there are a few things I've learned from that. For one, runout and concentricity are different animals. The Sinclair I linked is actually a runout fixture, and your ammo is not straight until measured so on it. It is not a concentricity gage, and that's fine.
Get your ammo straight first, and it will be concentric as well.

Sinclair's mandrel system is very useful on the bench for more than turning. I use it for necking up while forming wildcat cartridges, and I run every neck over an expander just prior to bullet seating. This pushes any thickness variance outward, allowing straighter seating, and lower TIR off the ogives.

The neck mic is a must for culling brass. If you ever hope to keep straight ammo, you need to cull out thickness variance as measured on the necks(it runs full length of the case). Otherwise, sizing brings out the devil in your brass. Thick areas springback more than thin areas, and you end up with a batch of bananas that only get worse with each sizing. This is not straight ammo(even if made concentric).

The neck turner works fine. Nothing fancy. Just slip a feeler between the mandrel and cutter. Trial & error a few culled brass, till it's perfect. There are different angle cutters available from Sinclair for different shoulder angles(you turn up onto the shoulder a bit). I have never turned brass by hand turning cases. Always used a case lathe. It's enough pain even at that.

 

I disagree with the statement: "And don't qualify with brass weighing, as this may not correlate to capacity(unless it's leaves the pack in an extreme)." Case weight always correlates to "capacity" at peak pressure when the case is pressed hard against the chamber walls and bolt face.

Cartridge brass is typically the same metals in the same proportions. Some's thicker walled than others. And there's a difference in hardness. But the mass is virtually equal across all of them; about 2163 grains per cubic inch. The volumn of the brass itself is subtracted from the volumn of the chamber and what's left is the volumn of the powder burning space behind the chamber's mouth which means the working capacity of the chamber won't ever change unless the weight (volumn, mass) of the case does.

So weigh your brass then sort 'em into a 1% spread of their average weight. That's close enough to shoot as accurate as the rest of the stuff is to put the bullet where you want it.

 

There are primer pocket depth, flash hole and case head/extraction groove/rim differences that throw off weight checks -as capacity.
These do not correct themselves under pressure.
I'll concede that some lots of brass prove to more or less correlate. But there are occasional anomolies even in the best brass, so it's capacity checks or assumption.
If it matters to you, verify it.

 

Variations in head stamp character size, quantity and depth will vary too. Neither does the variations in primer flame size and duration which cause more accuracy problems than a 1% spread in case weight or volumn.

All this aside, it's interesting to me that some folks do everything in the benchrest book to the nth degree to shoot their bullets as accurate as they can. Then others do a few simple things and shoot ammo testing groups smaller than and more often than benchrest records. There are reasons this happens.

 

Sorry Bart IMHO you are dead wrong on this issue. Am in Colorado with my Smith who is a HOF Shooter World Reacord Holder etc and one of the best builders on the planet and I mentioned to him that this subject is being debated again and he just shook his head. The internal capacity is all that matters and the weight of each individual piece of brass has nothing to do with internal capacity--sorry but that is a fact. Internal capacity drives pressure period.

 

Sorry Bart IMHO you are dead wrong on this issue. Am in Colorado with my Smith who is a HOF Shooter World Record Holder etc and one of the best builders on the planet and I mentioned to him that this subject is being debated again and he just shook his head. The internal capacity is all that matters and the weight of each individual piece of brass has nothing to do with internal capacity--sorry but that is a fact. Internal capacity drives pressure period.

 

Boss exclaims:

Sorry Boss IMHO I am alive right on this issue. Am in Colorado and my Smith who is a multiple time National champion, various Record Holder etc and one of the best builders on the planet and when I mentioned to him years ago that this subject is being debated he just shook his head. The internal capacity at peak pressure is all that matters and the weight of each individual piece of brass has everything to do with internal capacity--sorry but that is a fact. Internal capacity is equal to chamber volumn minus case mass volumn and that is only accurately attained at peak pressure period.

He's built rifles on Winchester Model 70 actions with standard SAAMI chambers that shoot 10-shot through 40-shot test groups from full length sized cases at 600 and 1000 yards smaller than benchrest records for the same number of shots per group.

 

Bart:

..and

Boss:

Well, your both barking in the right direction..

In reality the chamber volume, case volume, and where the bullet is all change as pressure builds up during the ignition/burn sequence. Then you throw in chamber temperature and burn retardants (lube, etc) into the mix.

The chamber expands, that's what strain gauges detect when they measure chamber pressure. The case of course expands with it. Even the bolt can deform and snap back. The bullet starts to move down the barrel at a relatively low pressure. Max pressure does not occur until the bullet is a couple of inches down the barrel.

So this dynamic set of events are hard to predict. To model it, one has to go to an engineering firm that specializes in fluid flow computational analysis, and further, the modeling software they use MUST be able to handle a moving object in the stream, as well as changing volume - there are only a couple of very expensive packages that can do this kind of modeling.

Well, outside of that we experiment and try different case prep processes to try and find the factor(s) that makes the most difference. It's not exact, and that leads to comments like the above. The bottom line, think through and consider ALL factors that influence the burn sequence, consider that steel DOES deform and move about, then spring back. Then prioritize and select those factors that you think will make the most difference to your shot-to-shot consistency.


Jay
Kyle Precision Arms

 

looking into getting some trimming gear too. what do you all think of the fosters case trimming tool. i have the one for doing case lengths and want to now trim neck walls to the same thicknesses so i get even releases.does the fosters system work and get it all square and good. cheers