Sinclair NT-4000 Neck Turning?

[jeffwhip]

This is my "first rodeo" at neck turning. I just got done turning some necks on my 280 AI Nosler brass over the weekend. The question I have is that most of the brass came out very uniform. The measurement middle-way up the neck is .0125, but when I take a measurement just below the neck, my measurement is .0130.

1. So my question for you guys, does this .0005 disparity really matter? Or is this close enough for govt work?

2. I do have some brass that are measuring .0120 on one side and .0125 on the other because I have my cutter set at .0125. Is that good enough?

3. Do any of you cull the brass if there is a certain disparity in the neck thickness or do you organize your brass according to overall weight?

4. What criteria should I use to cull brass?

Thanks in advance!

 

[Mikecr]

What criteria should I use to cull brass?

First, thickness variance(as measure at same datum on necks).
Second, H20 capacity of fully fireformed brass.

You didn't asy what your chamber neck is, or what your brass measures before turning.

 

[jeffwhip]

I have a 280 AI tight neck gun stamped .311. Before turning, I measured a few rounds and noticed a min of .0125 so I decided to turn them as little as possible. There are obviously some rounds that are .0120 because there has been no brass removed in these areas. Do I cull these? Thank you so much for the help as this is my first adventure into long range shooting.

 

[Mikecr]

I wouldn't worry about .0005 variance with a few. You've improved things enough, and there is clearance.
There is just not going to be any gain in further worry about it.

 

[SBruce]

Hello Jeff,

I'm not sure how you're getting some .013 measurments when the cutter/turner is set for .0125.? Are you using a ball or case neck micrometer? Calibers can give you false readings due to the flat/square edge of the blades.

Did you chamfer/deburr the case mouths prior to turning? That seems to help some too.

 

[jeffwhip]

Ok,

Here is my exact measurements. I'm measuring my cases with a nice Sinclair/Starrett ball micrometer.

.311 = 280 AI Chamber
- .284 (Bullet diameter)
.026
divided by 2
.013 neck thinkness (maximum)

When I measure the thickness of the neck wall with my Sinclair/Starrett ball micrometer, most of the cases measure anywhere from .0125 - .0130 (before cutting) up to the base of the neck. There are some cases however, that measure .0120 in places. So I set my cutter to cut .0125. This leaves me with a couple of problems:

1. The cases that are only .0120 on one side are not being cut at all so now I have some cases that are .0120 on one side and .0125 on the other.

2. Even though I have the 40 deg carbide cutter to match the 40 deg shoulder on my 280 AI case, when I cut so that there is a slight cut up into the shoulder (as depicted in the Sinclair manual), I am left with a case that measures .0130 right up against the shoulder and .0125 throughout the rest of the neck.

It almost seems as though the 40 deg cutter is not even and is off by .0005" on the angled end against the shoulder. I don't dare go into the shoulder any more. So:

1. Has anyone seen this before?
2. Should I call Sinclair and have them send me another 40 deg cutter?
3. Should I cull out all the brass that measure less than .0125 or does this really matter?

Thanks

 

[Mikecr]

Did you COW fireform these cases? Curious if your shoulder angles could be too high.
I wonder if you have a standard 30deg cutter(3300) instead of the 40deg(3340).
It would have been nice if Sinclair had stamped a # on the cutters.

You basically have a donut with this that could come into play if you seat bullet bearing there.

 

[jeffwhip]

Mikecr,

These are brand new 280 AI Nosler brass and have never been fired. However, I noticed that what Sinclair sent me was the NT-3140 which is supposed to be used with the NT-1000/2000 models. They did this even though they sold me the NT-4000. I'm going to call them tomorrow!

 

[SBruce]

OK, I see how and where you're getting the .013 now.

I never measured any of mine down that close to the shoulder, because it's below where I seat the base of the bullet.

Since you've got basically .002 clearance between loaded round and chamber neck.......I would guess that the .0005" difference on some necks wont hurt anything. But the only neck turning I've done was all the way around for a true tight neck chamber.?

If you were going for a fitted neck or .001 clearance, I personally would turn them down to .012 all the way around. That however, would require a tighter neck chamber to achieve.

 

[jeffwhip]

SBruce,

I do have a tight-necked chamber. I've thought about turning them all down to .012 but was afraid to take that much off. It makes sense that if my cutter is set to .0125 that it would skip over any portion that is less than that.

So, for now I thought what I would do is measure my trimmed cases and separate any case that is less than .0125. After I find a load, I'll load some up in these cases and see if there is a difference in accuracy.

What say ye?

 

[SBruce]

Sounds like you're on the right track, and using the right tools for the job (cutter angle may be in question however).

I'd call what you've got more of a "Minimum Turn" rather than a true "Tight Neck", but that may just be jargon speak. The benefit of a minimum turn neck is that you don't have to turn it all the way down. We don't have to make two passes to get the round to chamber, we can just take off the high spots, much as you've done so far.

You certainly can take off another swipe, it wont hurt anything, but I don't see it as a benefit in this case. It will just mean more working of the brass on fireing/sizing. Especially since you'll probably want at least a couple thou neck tension on the bullet...........You'd have a .308 loaded round and it will expand to .311 and spring back to .310 when fired. Then, it'll get squeezed down to .305 or .306 in order to have that .002 tension once loaded. You'd in effect be working the brass as much as .005 every reload.

Now, that being said; if your chamber was a .309, you would want to turn all the way around. In bench guns, we can do this and not even have to resize the case. It'll expand .001 to fire, spring back that same .001 and then we can seat a bullet with just enough tension to hold it in place. Not really something that should be done with a hunting rifle IMO.

I'd be suprised if you see any difference in accuracy from the ones you've done already and the ones you go all the way around on. But, if you do; let me know. I'm not too old to learn something new

 

[TOM H]

Ok,

Here is my exact measurements. I'm measuring my cases with a nice Sinclair/Starrett ball micrometer.

.311 = 280 AI Chamber
- .284 (Bullet diameter)
.026
divided by 2
.013 neck thinkness (maximum)

When I measure the thickness of the neck wall with my Sinclair/Starrett ball micrometer, most of the cases measure anywhere from .0125 - .0130 (before cutting) up to the base of the neck. There are some cases however, that measure .0120 in places. So I set my cutter to cut .0125. This leaves me with a couple of problems:

1. The cases that are only .0120 on one side are not being cut at all so now I have some cases that are .0120 on one side and .0125 on the other.

2. Even though I have the 40 deg carbide cutter to match the 40 deg shoulder on my 280 AI case, when I cut so that there is a slight cut up into the shoulder (as depicted in the Sinclair manual), I am left with a case that measures .0130 right up against the shoulder and .0125 throughout the rest of the neck.

It almost seems as though the 40 deg cutter is not even and is off by .0005" on the angled end against the shoulder. I don't dare go into the shoulder any more. So:

1. Has anyone seen this before?
2. Should I call Sinclair and have them send me another 40 deg cutter?
3. Should I cull out all the brass that measure less than .0125 or does this really matter?

Thanks[/QUOTE

With a .311 chamber your loaded rd should be .309 that gives .002 clearance then subtract bullet .284 is .025 half of that is .0125.

when you did your math you had .311 less bullet .284 you had .026 not sure how you did that but that should of been .027 less clearance .002 that is .025 half of that is .0125.

what I do is get a feeler gauge
Feeler Gauge | AutoZone.com

You can use them to set the neck thickness on the neck turner. You could also do a loaded rd @ .308 and I hope you got the expanders with the neck turner.

I have two 280AI and I was suprised to see .311 chamber my loaded rds are .311 most tight neck 7mm are .310.

Well good luck

 

[jeffwhip]

You guys have been great! I'm wondering if I possibly messed something up?

1. Should I have run my brass through a Redding S - Bushing Style Full Sizing Die BEFORE or AFTER I turned the necks?

2. Also, I'm reading through the directions on this Redding Die and don't understand how to set this thing up. The directions talk about putting the appropriate bushing into the die but it didn't come with any bushings? The directions say to subtract .001 from my loaded cartridge (.309) = .308. How do I adjust for this?

Thanks!

 

[Mikecr]

Ok, I gotta ask, have you read any reloading books?