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Posted: 4/26/2012 1:02:16 PM EDT
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I've been playing around with my 30-06 dies preparing to reload a bunch of ammo. One check I made for adequate neck tension was to see if I could (manually) push the bullet into the case. Yes, I could.
I checked the OD of the case neck after sizing (before seating) and after seating. The OD of the case grew by only 1 mil (from 0.333" up to 0.334"). I checked this for the LC Match brass and LC military brass I have. In both cases, I saw only 1 mil increase. I checked the bullet diameters (SMK and Wideners), both were 0.308". I checked neck diameter for four bullet and case combinations. In all cases (all bullet and brass permutations) I could push the bullet into the case. I think this means the expander ball in my sizing die is too big. Do you agree? Should I hone it down to a smaller diameter? What other solutions are out there? ETA - The die is a Dillon FL sizing die. Expander ball looks to be made of carbide, so honing may not work. Expander ball is 0.308" diameter. Cases sized without expander stem in die come out of die at 0.328" OD (before seating). If I eliminate the expander ball/stem, the neck tension is adequate to retain the bullet. |
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Had a similar problem not too long ago.
Responses I got are here: Neck Tension Thread .308 sounds way big on the expander ball. I think the die makers expect some spring back so they make the expander ball pretty close to the bullet diameter. The .3065" expander ball in my RCBS die works fine. |
| I have ground down expander plugs a couple of times, simply by chucking them in a drill and turning them against a sharpening stone. Measure with a good micrometer as you go. However, if you's is indeed carbide, that probably won't work. Dillon might be able to swap it for a smaller one. I don't know if those made by other companies might fit. |
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Here's an odd tidbit.
I got out my Redding die and measured the expander ball diameter. It is right at 0.3065", as opposed to 0.308" for the Dillon die. I lubed a piece of brass and ran it thru the Redding die, expecting a smaller neck OD. Here's the rub - instead of producing a smaller neck OD than the Dillon die, the neck OD was the same. After measuring the Redding expander ball, I was hopeful that die would do the job. I was unhappily surprised the brass was no different. What is going on there? Maybe I should get the Redding's old steel expander ball out and hone it down for this operation. |
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Okay, hard to say where this is going, but to start with you can't assume you know the brass thickness and that throws out the idea of assuming the bore based on measuring the OD (with the wrong instrument).
For starters, getting the ID on a piece of brass isn't easy. Unless you are trimming that brass and know the thickness, don't assume you can judge the ID by using an instrument with an uncertainty of 0.0015" to measure in the same range. You would need a few more pieces of information to know for sure what your ID is after the size die. Also, measuring the OD of the ball with less than a 0.00005" capable micrometer may also be a risk if you want to judge within 0.0005". Lets assume for a second that your calipers gave you a true indication that the ball OD is larger than 0.3065". Unless we know the thickness of your brass to less than 0.0005", then the error is doubled and you won't know anything to less than 0.001" which is half of what we are discussing. Unless most brass is trimmed, you can't assume the thickness doesn't vary by at least that much in terms of runout alone, then also add the average thickness uncertainty. Gage pins are the best method. (Watch Ebay or Craigslist to snag a set of gage pins in the sizes you want to measure.) If you take a micrometer to the OD of the neck while expanded over a projectile, you may be able to assume the brass thickness if you take lots of readings and average them. This is because projectile ODs are much more reliable than brass neck thickness and keeping it stretched over a good round bullet is like using the bullet as an ID gage. If we get an OD and thickness this way, you can then very gently try an take the OD readings after the size die the same way, but be aware that gage pressure will play a role in the error. You will need to take that diameter in several places and average. In the end, if your force test tells you that your neck tension does not make you happy, you may need to look into bushing dies and keeping track of the brass thickness by lots. If it really matters to you, neck turning and annealing is the only answer. It isn't likely to matter for short line ammo (up to or less than 200 yards). Before you assume this neck tension is too low, slam the bolt on one with no charge or primer to see if it is good enough and then do some accuracy testing. Getting about 0.002" is a good starting point and that should be easy with a good set of standard FL dies. |
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Quoted:
Okay, hard to say where this is going, but to start with you can't assume you know the brass thickness and that throws out the idea of assuming the bore based on measuring the OD (with the wrong instrument). For starters, getting the ID on a piece of brass isn't easy. Unless you are trimming that brass and know the thickness, don't assume you can judge the ID by using an instrument with an uncertainty of 0.0015" to measure in the same range. You would need a few more pieces of information to know for sure what your ID is after the size die. Also, measuring the OD of the ball with less than a 0.00005" capable micrometer may also be a risk if you want to judge within 0.0005". Lets assume for a second that your calipers gave you a true indication that the ball OD is larger than 0.3065". Unless we know the thickness of your brass to less than 0.0005", then the error is doubled and you won't know anything to less than 0.001" which is half of what we are discussing. Unless most brass is trimmed, you can't assume the thickness doesn't vary by at least that much in terms of runout alone, then also add the average thickness uncertainty. Gage pins are the best method. (Watch Ebay or Craigslist to snag a set of gage pins in the sizes you want to measure.) If you take a micrometer to the OD of the neck while expanded over a projectile, you may be able to assume the brass thickness if you take lots of readings and average them. This is because projectile ODs are much more reliable than brass neck thickness and keeping it stretched over a good round bullet is like using the bullet as an ID gage. If we get an OD and thickness this way, you can then very gently try an take the OD readings after the size die the same way, but be aware that gage pressure will play a role in the error. You will need to take that diameter in several places and average. In the end, if your force test tells you that your neck tension does not make you happy, you may need to look into bushing dies and keeping track of the brass thickness by lots. If it really matters to you, neck turning and annealing is the only answer. It isn't likely to matter for short line ammo (up to or less than 200 yards). Before you assume this neck tension is too low, slam the bolt on one with no charge or primer to see if it is good enough and then do some accuracy testing. Getting about 0.002" is a good starting point and that should be easy with a good set of standard FL dies. Sir, I've used calipers and mics with vernier scales for quite a few years. For my purposes I've never felt I needed measuring accuracy greater than four decimal places. While I don't have the exact dimensions of each of the die components I use nor the case neck thicknesses I will say that in most cases I attempt to achieve a case neck inside diameter of .002" less than the OD of the bullet. Yes case neck thickness do vary and for practical purposes the actual ID of the case neck after resizing and expanding is between .002"-.003". That's why I've use Sinclair neck expander mandrels for many years not in an attempt to make the case neck tension as uniform as I possibly can without turning the outside neck diameters. My recommendation for the OP is to measure the case neck ID after resizing without using the expander ball. FWIW, a lot of die makers use dimensions that render the ID of the case neck in excess of .005" less than bullet OD which is excessive for my purposes. Without replacing the Dillon dies using a carbide expander ball with an OD of .308" is going to be a problem because even with a carbide ball dragging the ball from the case interior across an excessively small resized case neck is likely to distort the case shoulder and cause variations in case shoulder length. My solution for these problems is to use a Redding type "S" die with a bushing sufficient to reduce the case neck outside diameter sufficiently to provide an inside diameter of .003" less than bullet OD, ie: .305" for a .30 bullet. I use a carbide expander ball in all of my Redding rifle dies and the combination of using bushings, carbide expander balls, and case neck expander mandrels, and neck annealing make for a very uniform case neck tension in my experience. Just my humble opinion. 7zero1 out. |
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