I just finished forming, sizing ,trimming ,and neck reaming some 308x1.625 cases from 308 cases. For me I then inside neck ream with a .311 reamer after neck sizing in a 308x1.5 die.
Is outside neck reaming better? Seems like all the jb guys outside neck ream.
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The theory is that outside neck turning against a mandrel makes for a more even wall thickness. They say a reamer will follow the thin side of the original neck. I have no opinion one way or the other. I outside neck turn but only because that is the tooling that I own.
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I want to add to Bud's list which is excellent. The neck needs to be a very tight fit on the on the neck-turning mandril. You need to lubricate new cases as they will gall and deposit brass on the expander and maybe the mandril. AMHIKT! Lubricant makes a difference! Imperial sizing wax gave 0.0005 to 0.001 THINNER necks because it makes a thicker film. Graphite gave the thickest turned neck, but it is messy.
Was all this effort important? I could not see a difference between Norma brass and turned neck Norma brass. This was in a custom 308, with minimum chamber but not a "tight neck" set-up. The Norma brass was very uniform in the turning, I trimmed some Reminton brass and saw a large difference in the amount turned off between the cases. I never did a firing comparison with the Remington brass.
I never tried a reamer die, no information.
I think the jacketed folks must have done a comparison of methods. Too bad Precision Shooting mag is no more.
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A reamer follows the path of least resistance, leaving a diameter the size of the reamer.This is an absolute. Outside neck-turning gives an even wall thickness with careful work.
As an example using the .308 Winchester case in a Production Class rifle, I outside neck turn using the following procedure:
Once setup, I process 340 cases at a time. This gives me a few spares for the cases necks that have splits in them as you progress or that split anyway in the course of a year's competition. Lots of work and sometimes I'm not sure this dedication is needed.
Farm boy from Illinois, living in the magical Pacific Northwest
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Maybe this was mentioned earlier…..
Not for a “production” rifle, but for a custom chamber. Mic a loaded round. Compare that to the neck ID of the reamer/chamber. (Most gunsmiths will stamp that dimension on the side of the barrel.) The mic’ed diameter of the loaded round must be smaller the chamber neck diameter. Most people would promote a minimum clearance between the loaded round and the chamber of 0.0005” per side or .001” total. Room is needed for the brass to expand and not be constrained by the chamber during ignition. Depending on the brass thickness of the neck, outside neck turning might be needed, to produce the needed loaded round clearance.
This is for rounds where not a lot of brass is removed when reducing the case length. But…..due to “brass migration” during excessive case length shortening, it might be needed to inside ream and outside turn the necks. There is no magic “always must do”. Careful dimensional examining of all involved “puzzle pieces” will be needed to determine the route to be taken that is needed. And every brand of brass does not have the same neck wall thickness.
My most recent adventure involved a minimal case length shortening of a Lapua 6BRmm norma case, necking the mouth diameter down to .22 caliber and then the turning of the necks down to slightly less than 0.013”. The batch of (235) cases were fired slightly under 5 times each this past match season, with no failures or problems.
Tom
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I don't remember a head to head comparison of turned to un-turned brass and jb's. Seemed like all custom chambers were tight by design. Bud gave the textbook answer for turning brass and Steve was right about using graphite.
Neck turning to control tension has been given the kabach by others including Bottiger and more recently John Alexander in his recent article in TFS 279. As he put it:
“Apparently, this is just something that some reloaders believe they have seen or just know is important because it sounds logical.”
I think many would agree that the only reason to turn a case is for alignment to the bore. However the accuracy improvement with neck turning is dependent upon the equipment being used isn't it. Bud said he turns to at least 75% cleanup, discarding the outliers and he is turning neck thickness of .015. I fully agree. This is logical, easy and even fun to do.
But a custom action, reamer, barrel will benefit more from neck turning then a production rifle. Right? So from the low end of the spectrum, that being a production rifle, how much is there to gain from neck turning? I guess that last question can never be answered. Every over the counter rifle has the potential of having a variation of bolt face to bore alignment and the degree of benefit truing up the case neck will bring.
It is possible maybe even probable that cleaning up the necks to .015 will improve accuracy. It is also possible that the alignment is so pathetic on an over the counter rifle that even truing up the neck won't even help.
For some it just isn't going to help much is it. For others, turning necks for production rifles even those having oversized chamber necks will put the bullet closer to the center of the bore. For the time being I'll continue neck turning just because I think its the right thing to do. Guess that makes me guilty of what John describes as doing someting "....because it sounds logical".
I asked a question earlier and if anyone has any reference to it I am curious what measure cast bullet shooters use for tolerance when describing a tight neck chamber. And yes I do miss the magazine Precision Shooting. But we do have the TFS on CD. For people like me that helps. Thanks, Bill.
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Good description Bud. You say, "Lots of work and sometimes I'm not sure this dedication is needed. "
I also have neck turned lots of cases and have the same doubt about the value in a production chamber, or even a tight necked custom chamber for that matter since I can't remember any such testing in 20 years of Precision Shooting. The next time you do a batch why not run a quick test - five groups each of unturned, < 75% clean up, and > 75% clean up. I wish I had done that on the last batch I turned. My present batch of match brass is going strong but I will do the test on the next batch if I do another.
This kind of test is so easy to do when we have any doubt about extra work in reloading. And let's be honest, we do a lot of hooky things because we hope they help. Too bad we do the comparison testing so seldom.
John
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1- maybe a little shorter. Mainly need to blow out the shoulder and side walls, especially on 06 cases.
2- That's all. With 308 cases and their fatter profile the brass near the base gets squished out and needs to be filed down while spinning in a drill press, not so with 06 cases.
When forming all i'm doing is pushing the shoulder back, a lot. But once started it just keeps on going and I wind up with a really long case neck and a short fat body.
Thanks all for the opinions, it does help.
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Ross have you always inside reamed? Since I've only outside neck turned these past 30 years its all I know.
I think that turning the outside necks down to and including the shoulder would maybe improve fire forming to prevent inside bulging where the neck meets the cast body. 2.015 down to 1.625 seems to moving a lot of brass around. Is it possible you need both?
I didn't help did I. More questions than answers. I'm looking forward to what others think. Take care, Bill.
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Just so you all understand, I have to ream. I either use an inside reamer after sizing or I need to have a custom expander and mandrel for an outside reamer. John Ardito didn't worry about this in my opinion, he just opened up the case mouth to hold the bullet by the GC. Maybe that's all I should do too.
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Ross,
I might have missed it but do you know the inside diameter of the neck area of the chamber? If you know that value, then your comment about the case expanding 0.015” per side makes sense. With the loaded round measuring 0.343” and after firing the case neck measurers 0.343” so the case must be expanding a bit during firing to briefly fill the neck area and then the brass springs back to its initial dimension.
I cannot tell you which is best as I have only inside reamed once. But I have neck turned a lot of cases over the years. Not because I thought that was the better route with no “scientific” basis to do that. That’s just what I did and local shooting buddies coached me into that practice. I have only radically shortened a case once and that was for a revolver so there was no reaming or neck turning involved.
However, as interesting for your project, is what size neck sizing bushing will you use to develop a bit of “grip” on the bullet, as it is seated into the case? 0.342”, 0.341”, or…..maybe no grip will work for you. This is some experimenting that surfaces as you work to develop an accurate load. Suggestion….try to use a mic to take your measurements instead of a caliper. A mic is more accurate.
FWIW
Tom
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I don't recall reading anything (starting long before the Internet) in the way of favorable comments regarding inside neck reaming. As a result, I've always done outside neck turning for the last forty or more years without questioning the process. My results have always been satisfactory for what may be my own lower standard of excellence.
I don't claim outside neck turning is the best method in all situations because i'm not familiar wtih neck reaming - perhaps a mistake based on "conventional wisdom" reasoning. I've worked with many standard cartridges and a bunch of wildcat and Improved cartridges from the .22 Long Snapper to the .411 Hawk. Outside neck turning worked well for all cartridges that required the procedure. I don't know whether reaming might have been better in some instances, but there are probably some things not worth worrying about now.
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basics ... well, my thoughts ... which by definition and tradition, qualify as basic ...
case neck clearance:
1) safety : neck seated cartridges need the neck to expand a little to release the bullet ... to keep pressure down ... well, maybe ... in low pressure loads with soft castings, maybe not...; or not much ... ... but they say we are poking the bear if we run no neck clearance ...
2) bullet guidance ... we all think that a bullet started straight has a better chance of less deformity as it goes through the trauma of adapting to the rifling at it's hundred yards a second crash-meeting ... the case neck holds it straight before firing ... and the tighter the clearance the straighter ...
but the neck expands upon firing and leaves the bullet hanging in mid air subject to hurricane force gases blowing by in a haphazard manner ... ... doesn't make any difference what the non-fired clearance was ... heck, that screws up our guidance scheme ... only no clearance at all would keep guiding the bullet as planned ... but then there is that poked pressure bear ... is the bear real ... with soft castings ? ...
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could test to find out, if anybody had a pressure gadget ...
meanwhile, we could very likely think about heeled cartridges, ... like the 22lr, where if you have $200 extra for the good stuff, you can buy a brick of 500 that will shoot 489 of them into a half minute ... they have zero neck clearance in a match chamber ...
maybe that old Martini 310 trainer had the right idea all along ? ... match chambered Lilja with a heeled 308BR anybody ? ...
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just some thoughts ... as i warned, consider the source ...
ken
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Tom described the how and why's very well. The only thing I would add is over all case length. Fireforming three cases three times will give you what to expect for final overall case length.
Verify the following numbers before we go any further.
The wall thickness after inside reaming of the formed case is .013-.015.
a loaded round is .343" / chamber neck is .346
If you have:
You will have a final loaded round that will measure .336 to .342 with neck tolerance of .005 to .002 per side or .010, .004 overall.
Instead of reaming for neck thickness and removing the doughnut you need to ream to remove the doughnut and then outside turn the necks down to and including a light cut on the shoulders (to prevent future doughnuts). Personally I would stop at .0015 if this were my first run at tight necks. If you make a mistake the only variable you have is to size the bullet to .311 or .310 go fit the chamber.
Assuming that you took that approach, you would cut out the doughnut and then outside neck turn. To do that you'll need to fall back to what Bud described including sizing down the case neck, expanding back to for a tight fit on the mandrill of the neck turner you'll have to buy and then neck turn. I recommend a couple practices pieces with one giving you and overall neck tolerance of .003 before you make the final cut. After getting to the final cut I would fire form three and make sure all stays ok before I'd cut a hundred or 200 pieces. As I said if this were my first attempt at neck turning I would have at least .0015 overall clearance.
So no matter what you do you'll have to neck turn to get the wall thickness exact. As Bud said, a reamer follows the path of least resistance leaving a diameter the size of the reamer and it does not true the neck. Good luck, Bill.
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Are you referring to "More Variation in Neck Tension" in 279? Bill C.
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Ya'll: I inside neck turn because when forming my cases for 308 cases, the new OAL is down into thicker brass from the 308 cases. I get a dougnut right of the bat and sine my outside neck diameter is already correct , I just inside neck ream and I'm done with that part of forming. Also at the moment I do not have an inside mandrel that is the correct size to support the case neck during outside reaming. I appreciate all the replys, cuz after all I did ask a question. Do you think I could get better results( more even neck walls) by outside reaming?
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That makes perfect sense. My hand turning is with off the shelf stuff like the pumpkin. Wouldn’t you be able to ream out the built up area and then outside neck turn. Maybe just to clean up the neck 75%? Bill.
Or is this in a tight necked chamber?
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Ross, tight on jb’s is half a thou on each side. One thou total. How much clearance do you have factored in? What’s the +/- tolerance is on loaded cast rounds?
I’ve never worked with cast unrestricted which is where a short .308, custom reamer, custom barrel, tight neck chamber sound like it would be shot. Little envy here.
Sounds like one heck of a lot of fun. Bill
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John Alexander
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cohenmj660
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