Neck Turning Question

[ehkempf]

I am new to the centerfire benchrest game of neck turning. I am not new to benchrest in general as I have shooting IR 50/50 for years (only at the club level), and have been an avid woodchuck hunter since my teens. I have and do own several 6MM BR and 22 BR, but they were all build with no turn in mind (.272 and .254). Well I have taken the plunge and bought a used 30 BR with a .330 neck. The 30 BR came with 50 pieces of Lapua brass, and a Borden FL die set for .326 neck tension. I currently do not have a ball mike, but do have a dial caliper (I know I really need one). Using what I got I came up with an average of .010 neck thickness on the used brass. I have some new Lapua brass and after expanding out to 30 cal., I measured the wall thickness at an average of .012. So here are my questions. Based on my measurements does taking off .002 seem right, or was the original brass that I got not taken down enough? This question is based on the idea of only .001 of clearance all around (.010+.010+.308=.328). Another question is, assuming that the .002 to be taken off is correct, can that much be taken off in one pass with a neck turning tool, or do I need to do it in smaller increments? Like I said I have never turned brass before, so this is all new to me and I have a lot to learn.

Thanks,

Ed

 

[zimmden]

For a .330 chamber neck you need .010 brass to give you .001 clearance. Measure the loaded round to make sure it comes out to .328. Use 2 passes to achieve an accurate smooth cut. Take off about .0015 on first pass and .0005 on final pass. After 1 or 2 firings, you may want to take off .0005 more. Make sure the inside of neck is clean and the mandrel fits the neck closely. A ball mic is needed since the caliper can only measure in a very limited area of the neck.

 

[Charlie/KY]

Ed, go to 6mmbr.com and open up the article on the 30BR which is on the left hand side of the page. It goes into detail on turning your Brass and load developments. This is how I got started with the 30BR 4 years ago. The best article out there on the 30BR.

 

[abintx]

Turn whatever you need [no specified amount] so that the OD of the loaded round measures .328" over the bullet's pressure ring if it has one. Ronnie Cheek's bullets, for example, have a .0003" pressure ring over the bullets shank diameter. Bushings of .326", .325", .324", and I've even seen .323", will aid with tuning the load; .325" and .324" seem to be used the most. Ken Markle once told me he took off .015" in one pass as a test. Two passes, one taking off the majority of what's needed, followed by a second as a clean up, works well for me.

 

[mks]

Ed,
You have received some good advise. One more thing: just because the neck is labeled 0.330, don't assume it is. I have one labeled 0.330 that is actually closer to 0.331. Start with one case and shave off tiny amounts until the neck barely fits into the chamber with a seated bullet. Then you will know the actual size of the chamber according to your measuring tool. Keep this case with seated bullet as a reference. Afterwards when you measure reduced neck diameters with the same tool, you will have a better idea of exactly how much clearance you have created.

I am too much of a rookie to know what the best clearance is, but once cut, it is difficult to add brass back to the neck. But you CAN start with less clearance and then cut more later if you think it isn't working.

Keith

 

[Dwight]

Ed,
You have received some good advise. One more thing: just because the neck is labeled 0.330, don't assume it is. I have one labeled 0.330 that is actually closer to 0.331. Start with one case and shave off tiny amounts until the neck barely fits into the chamber with a seated bullet. Then you will know the actual size of the chamber according to your measuring tool. Keep this case with seated bullet as a reference. Afterwards when you measure reduced neck diameters with the same tool, you will have a better idea of exactly how much clearance you have created.

I am too much of a rookie to know what the best clearance is, but once cut, it is difficult to add brass back to the neck. But you CAN start with less clearance and then cut more later if you think it isn't working.

Keith

The one thing you have to be very careful with is not assuming that bullets are exactly .308. Mine measure over .308 and I had to cut more because of it.

 

[SGJennings]

Most of the shooters, both 30 and 6, that I talk to say that the trend is toward more total clearance.

On second thought, I don't know that it's a new trend. A Hall of Famer, who was gracious enough to talk to a newbie several years ago told me "Cut thin to win".

FWIW, Greg J

 

[Charles E]

Most of the shooters, both 30 and 6, that I talk to say that the trend is toward more total clearance.

On second thought, I don't know that it's a new trend. A Hall of Famer, who was gracious enough to talk to a newbie several years ago told me "Cut thin to win".

FWIW, Greg J

Well, it would be a trend for Mr. Boyer. From the 1996 Precision Shooting Annual, interview by Dave Scott entitled "Tony Boyer on Winning" (page 600):

Given that he turns his case necks for a mere .0002" clearance...

Though later in the paragraph:

Having experimented with both tighter and wider neck clearances than his present .0002, he contends that a good rifle will shoot as well with one as the other.

I believe, though Scott's language doesn't make it clear, that he's using .0002 per side, given that .0002 total would be .0001 per side, a fussy number... Could be, though.

And no, I didn't get an extra zero anywhere in there.

Edit:

To the original poster: You didn't say, but if it is a Borden-built rifle, and the barrel is stamped .330, it is .330. Jim checks. Many don't.

.002 can be easily taken off in one pass. Whether or not you can do it (never having done if before) is a different question. I forget how long it took me to make cuts where the final size was exactly what was wanted, but it was over a year. More, smaller cuts mean more changes to get close... 'Course, I'm a slow learner...

BTW, if you measure with a ball mike, you'll tend to get a reading that is a bit bigger than how things wind up. Those tiny little ridges flatten out, filling in those tiny little valleys. But the mike's big enough to only see the ridges. How much is this? Not much, maybe .0001 or .0002 -- what Mr. Boyer used to use as total clearance...

On thing that helps, at least helps to see. Take some Scotchbright, and pull it longitudinally along the neck. You're sort of cross-hatching the cut made with the turning tool. Now turn it again with no change to the cutter. Surprising, isn't it!

 

[SGJennings]

Don't know what the article says. Don't know what TB said when talking to the interviewer, don't know what * might have been lost in translation, don't know what might have been screwed up in the publishing process.

In his book, on page 116, he says that he turns to 9.2 and that this leads to a loaded round that measures 262 shooting in a 263 neck.

Take it FWIW, Greg J

 

[SGJennings]

Took me a min to find it, on pg 139, TB says

"Experiments on fitted chambers with a clearance under .001" showed no improvement in accuracy but created a potentially dangerous situation."

Again, take it for what it's worth, Greg J

 

[Charles E]

Mr. Jennings:

Your point being?

 

[SGJennings]

I said "take it for what it's worth". Meaning that it is one bit of information. Nothing more or nothing less.

Seems like you have a problem with me. Meet me anywhere half way and we can settle it face to face. If you have the gonadic fortitude.

 

[Charles E]

I said "take it for what it's worth". Meaning that it is one bit of information. Nothing more or nothing less.

Seems like you have a problem with me. Meet me anywhere half way and we can settle it face to face. If you have the gonadic fortitude.

Well, you've called me "arrogant." I just wondered if you were trying to add "liar." Best I can tell, I've not called you names. If you're trying to pick a fight, remember I'm an old man with a lot of disease. If I do fight, it has to be real final, real fast, before I run out of air. That what you had in mind?

Getting back to the thread, if we can trust the proofreading in Mr. Boyer's book, and with the effort Larry Costa put in, I'd bet we can, in Mr. Boyer's case, it looks like a current trend -- a change. Not something that was always the case. That was my point.