Neck tension question
- Thread starter Thaught
- Start date
It's diameter, so the .307",
How is the weather down there, is the rain over for you folks?
Also, here is a better answer
Neck Bushing Sizing
How is the weather down there, is the rain over for you folks?
Also, here is a better answer
Neck Bushing Sizing
Coyotefurharvester
Silver $$ Contributor
You may(will) see spring back that needs to be compensated for, in this case( no pun intended) expansion after pulled from bushing.
I bought 1 bushing assuming I knew what I wanted. Later I bought 3 more to bracket. Ended up using one size all the time. I would concider selling 3 cheap. I bought the plain steel bushings. Never saw any admantage to TiN coated ones. Steel bushings much cheaper. They are for 6mm.
Ned Ludd
Silver $$ Contributor
The correct answer is that you would select a bushing that left the necks at 0.307" after sizing. That would generate the requisite .003" increase in neck tension (i.e. interference fit) once the bullets are seated.
However, there are caveats to that in terms of the exact bushing diameter needed. As noted above by @Webster, bushings don't always yield the exact diametral value in the brass as the numerical value with which they are stamped. It is not uncommon to observe two or three different bushings, all stamped with the same diametral value to yield neck diameters of +/- .0005", or even .001", in actual use. Thus, you'll want to find one that leaves close to 0.307" neck diameter in the sized necks. That may mean a .307" bushing, or it could mean a .306" bushing that was slightly on the large side. Find one that gets you close and call it a day; for example, I wouldn't be concerned if the average neck tension turned out to be .0025" instead of the full .003". You can always test and determine optimal neck tension using precision as the readout, if desired, but worrying about it past half a thousandth not necessary for most applications.
In addition, springback of the brass can also have an impact as mentioned above by @Coyotefurharvester. In my hands, springback is usually worth about .0005", but I generally try not to move the brass more than about .001" to .002" farther than necessary. For example, I generally first re-size brass using a bushing die with a bushing that will leave the necks approximately .001" to .002" smaller than I want them to be at the finish. Then, I will use a mandrel to open up the necks that will leave them with the desired neck tension/interference fit. In my hands, .002" neck tension is usually the target figure. Because the mandrel will increase neck diameter (i.e. the bushing die leaves the neck diameter smaller than the mandrel), when the neck is opened up by the mandrel it will close slightly due to springback as the mandrel is withdrawn. I typically find that a mandrel of approximately .0015" under bullet diameter will leave the neck at approximately .002" under bullet diameter due to the extra .0005" or so of springback. In general, the total amount of springback can depend on how far past the desired dimension one has moved the brass in an earlier step, but as a working figure, .0005" seems to be reasonable for me. None of this is really rocket science in terms of the mechanism(s) by which it occurs, it's merely an experience thing...the more one has worked with various different brass, bushings, mandrels, etc., the better they will know approximately the correct bushing diameter they need to try first. If that bushing doesn't yield the desired neck diameter, some testing may be in order. For that reason, I generally experiment with steel bushings; they're cheaper than nitrided bushings and so a little less painful to find the correct size.
However, there are caveats to that in terms of the exact bushing diameter needed. As noted above by @Webster, bushings don't always yield the exact diametral value in the brass as the numerical value with which they are stamped. It is not uncommon to observe two or three different bushings, all stamped with the same diametral value to yield neck diameters of +/- .0005", or even .001", in actual use. Thus, you'll want to find one that leaves close to 0.307" neck diameter in the sized necks. That may mean a .307" bushing, or it could mean a .306" bushing that was slightly on the large side. Find one that gets you close and call it a day; for example, I wouldn't be concerned if the average neck tension turned out to be .0025" instead of the full .003". You can always test and determine optimal neck tension using precision as the readout, if desired, but worrying about it past half a thousandth not necessary for most applications.
In addition, springback of the brass can also have an impact as mentioned above by @Coyotefurharvester. In my hands, springback is usually worth about .0005", but I generally try not to move the brass more than about .001" to .002" farther than necessary. For example, I generally first re-size brass using a bushing die with a bushing that will leave the necks approximately .001" to .002" smaller than I want them to be at the finish. Then, I will use a mandrel to open up the necks that will leave them with the desired neck tension/interference fit. In my hands, .002" neck tension is usually the target figure. Because the mandrel will increase neck diameter (i.e. the bushing die leaves the neck diameter smaller than the mandrel), when the neck is opened up by the mandrel it will close slightly due to springback as the mandrel is withdrawn. I typically find that a mandrel of approximately .0015" under bullet diameter will leave the neck at approximately .002" under bullet diameter due to the extra .0005" or so of springback. In general, the total amount of springback can depend on how far past the desired dimension one has moved the brass in an earlier step, but as a working figure, .0005" seems to be reasonable for me. None of this is really rocket science in terms of the mechanism(s) by which it occurs, it's merely an experience thing...the more one has worked with various different brass, bushings, mandrels, etc., the better they will know approximately the correct bushing diameter they need to try first. If that bushing doesn't yield the desired neck diameter, some testing may be in order. For that reason, I generally experiment with steel bushings; they're cheaper than nitrided bushings and so a little less painful to find the correct size.
Thaught
Silver $$ Contributor
Weather is finally getting getting better, but sure appreciative of the rain. Filling tanks for cattle and game is so important.
I think I’m getting spring back because I FL sized about 100 peices at the same time, same die and bushing and 20 of them won’t seat a bullet firmly. Guess I’ll pull all 80 bullets and resize again so they’re all the same?
Here is some math using numbers provided. .310 loaded round at the neck. Subtract bullet diameter of .284 = .026 total brass thickness.
.307 bushing minus brass thickness of .026 = .281 inside diameter of sized brass. Ignoring brass spring back, consistency of annealing, off sized bushing, etc., this should give you .003 of concentricity fit.
Help us understand “won’t seat a bullet firmly.” Pull the other 80?
What size bushing are you using now? What is the outside diameter of a neck on a sized case? Can you measure the loaded neck diameter of several bullets to confirm the .310?
Edited: My guess is that you are currently using a .309 or .310 bushing. Close?
.307 bushing minus brass thickness of .026 = .281 inside diameter of sized brass. Ignoring brass spring back, consistency of annealing, off sized bushing, etc., this should give you .003 of concentricity fit.
Help us understand “won’t seat a bullet firmly.” Pull the other 80?
What size bushing are you using now? What is the outside diameter of a neck on a sized case? Can you measure the loaded neck diameter of several bullets to confirm the .310?
Edited: My guess is that you are currently using a .309 or .310 bushing. Close?
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searcher
Gold $$ Contributor
If you change brass lots or don't get your necks turned to the same exact thickness, you may want those bushings back..... Those thoughts are what keep me from getting rid of the horde of bushings I have - all idle bushings for the same reason as you encountered. You know a lot of people end up with a lot of bushings when they make plastic cases to hold dozens of them Ha!. (They are nice to have)
I'm confused! What size bushing are you using? If 20 will not seat firmly why are you pulling the other 80? Is the 100 brass all the same? Same brand, same number of firings? Same cleaning and prep?
Thaught
Silver $$ Contributor
Currently using .309. The problem is out of 100, 80 of them will hold the bullet and 20!of them won’t hold a bullet. My concern is that I need to pull all the loaded ones and resize everything the same with .307 so they are all the same?
But they will not be all the same. The 20 will be correct and the 80 will be to tight.
@Thaught, we are still lacking the information asked previously. Without that information, I would get a .308 and a .307 bushing and load enough rounds of each to test before I loaded a hundred. I think most want somewhere between .001" - ,003" interference fit (neck tension). And, I think they decide which they want for the particular gun, cartridge, load, brass, brass prep from testing the results that each provides.
Coyotefurharvester
Silver $$ Contributor
Do you have the expander/decapping rod in the die? If so, what diameter is the expander. It's usually -0.002 from bullet diameter.
Thaught
Silver $$ Contributor
I pulled the decapping/expander.
I’ve loaded thousands of rounds before and this is the first time I’ve run into this scenario.
This is a common scenario. If you follow the instructions I linked to above usually things will work out pretty quick. However, it isn't uncommon to end up having a drawer full of bushings with just a couple calibers. As @nmkid posted above. Also, when you change brass brand, skim necks, or anneal you may need to change out the bushing.
Quality type brass like Lapua, Alpha and others are pretty consistent with neck thickness. Some brands not so much and they will yield different interference fit with the same bushing.
Quality type brass like Lapua, Alpha and others are pretty consistent with neck thickness. Some brands not so much and they will yield different interference fit with the same bushing.
searcher
Gold $$ Contributor
If 20% of his brass won't hold a bullet - that is not "correct" - as they need to be able to hold the bullet. While the other 80 might be "tight" relative to those that are "loose" in the neck - using the tighter bushing is the only option unless he turns necks. Even then, he will still need to go with a tighter bushing
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