neck diameter confusion

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updatelee

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I used to use an rcbs die for reloading my 300wm and today my new redding comp die showed up, these use bushings to set the neck diameter. but here is where Im confused.

my lyman book sais my neck diameter should be 0.339, I measured some fired brass and its showing 0.339. There was a 0.338 bushing included in the box so this looks good. The redding manual sais to use 0.001 less then your fired brass shows.

now the issue is after I neck size them they have shrunk to 0.338 but the amax 208's im using basically fall right in, there is darn near no tension at all on them.

so I measured a few of my reloaded shells from the rcbs die and they are with bullets seated at 0.332 - 0.333

So im confused on what is going on here. Should I buy a smaller bushing ? is there something more to the story here that I am missing ?
 
Might depend on what brass you are using.; neck wall thickness will have a direct effect. Hole in sized case= sizing die ID - 2Xneck thickness. If you are goint to use a bushing die, you need to know what this dimension actually is.
 
Forget what they're telling you about the outside diameter of the neck. Everybodys case thickness is going to be a little bit different. Also, as you fire them more and more times, that case neck is going to stretch and get thinner. You know that little bit of brass that falls on the floor when you trim your cases? It's comming from somewhere :) Worry about the inside diameter. I just went and measured a few of my 300WM cases with my Mitutoyo digital vernier. They're between 0.305" and 0.3065" and 0.308" bullets (measured exactly) go into them just fine. How far the case neck stretches and how much it retracts once your die is out of it is going to depend on temperature, case wall thickness, the composition of the brass, how hard/soft it is from multiple firings, even down to how quickly you ran the die through it. Even then, it's still going to be ever so slightly out of round, due to the same things. There are too many variables to be splitting hairs over a thousandth of an inch because you're going to have that much variance, and that's all there is to it. To answer your question, go a thousandth or two under the size of your bullets. How do you know??? Feel them when they go in. If you can slide them in with a tiny bit of pressure from one finger, they're too loose. If you've got to stand on the press arm to force them in, or if you see that you're starting to distort the case, you make the neck a little bigger. Once you've got the die set to where the bullets feel good going in, do a bunch.
I hope that helps :) Cheers!!!
 
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well the reason I am concerned about outside neck diameter is because thats how the redding die is setup. you buy bushings for the outside neck diameter, not the inside... there doesnt accually seem to be anything at all ensures the inside diameter is set... ie the decaping rod is straight, the rcbs and lee dies's Ive used had a taper in them to resize the inside of the neck as well.

currently Ive got a 0.338 bushing in there because thats what it came with, so if you do the math

0.333 - 0.308 = 0.025 is how thick my brass is (x2'd)
0.025 + 0.306 = 0.331 is the bushing size I want then ?

so is the idea to maybe get a few different sizes and chase the bushing size down as my brass gets more used ? whats the point where I shouldnt be using it anymore ?
 
http://www.redding-reloading.com/techlinepages/bushingselection.htm
Bushing Selection
for Redding Bushing Style Neck Sizing Dies
(Revised 3/3/2003)

There has been some confusion regarding the correct diameter bushing that should be used with Redding Bushing Style Sizing Dies. The most common misconception is that the bushing diameter is determined by the neck diameter of fired cases or the neck diameter of the chamber that the reloaded ammunition will be fired in. The bushing diameter is related to the chamber neck diameter, but only indirectly, in that the loaded cartridges must have adequate clearance at the neck to allow the bullet to be released properly upon firing.*

The easiest way to determine the proper diameter bushing is to measure the neck diameter of several loaded or dummy cartridges with an accurate micrometer. (These dummy cartridges can be loaded with your old set of dies or a borrowed set.) Then, simply subtract 0.001" from the cartridge that had the smallest average measurement. This will allow for a slight amount of spring back and create a proper press fit for the bullet.

The above method of determining bushing size require that the cases being sized have a fairly uniform neck wall thickness or have been neck turned. If the neck wall thickness varies more than 0.002", it may be necessary to use a bushing a couple of thousandths smaller than your calculations indicate, and then use a size button in the die to determine the final inside neck diameter.

After loading your first few cartridges, it's a good idea to test the grip that the case neck is exerting on the bullet. The simplest method to perform this test is to press the tip of the loaded cartridge against the edge of your reloading bench with moderate pressure. The bullet should not be seated deeper in the case if you have sized at least one caliber of the case neck. If the bullet is seated deeper in the case, switch to the next smaller size bushing and start again.

It has come to our attention through customer calls and our own use of the bushing style sizing dies that in certain instances, a given neck sizing bushing will produce a case neck diameter that can be several thousandths of an inch smaller than the actual diameter of the bushing. This idiosyncrasy occurs when the neck diameter of the fired case is a great deal larger than the diameter of the neck sizing bushing, such as occurs when factory chambers are on the large side of the tolerance range and the brass is on the thin side. Typically, we have not noticed any problems until the case neck is reduced more than 0.008-0.010".

Solutions include, increasing bushing diameter to compensate and/or the use of a size button. Reducing the neck diameter in two smaller steps by using an intermediate diameter bushing will also help. More concentric necks will also result using this method, as the case necks are stressed less during sizing. Don't forget to properly chamfer the inside and outside of the case mouths and apply a light coating of lubricant to the case necks before sizing.

* We recommend that the neck diameter of the largest loaded cartridges measure at least 0.002-0.003" smaller than fired cases measured at the same location. This ensures that there is a clearance of at least 0.001-0.0015" all around the neck of the loaded cartridge. This clearance allows the case neck to expand and safely release the bullet upon firing.
 
Bullet Dia. + 2X neck thickness, minus .001-.002 is all you need to figure out bushing size. I have had .308 brass go 15 trips through the rifle without a problem. Run your brass until the primer pocket start to open up and primer seating become very easy. After 5-6 trips you may want to full length resize and check/trim your case length.
 
updatelee said:
JNG: ok sounds like 0.332 is what I need then, thanks.
Click to expand...

Powder Keg has the bushings, Ron (works at PK) had the same problem the other day with his .308. After neck sizing the bullets could be put in the case by hand. I believe he was going to get a .333 bushing though.

Take your die and a case and bullet down with you. Maybe they can try a couple of bushings down there for you on their loading press.

If the .338 bushing is just barely putting tension on the bullet then it would seem to me that you need to use a bushing .001-.002 smaller than that and not .006 smaller. :shrug:
 
thanks cyan1de I'll go down to the powder keg tomorrow and see what ron has to say.

if they are cheap enough it might be worth while getting a few, 0.332, 0.334, 0.336 that way as the brass changes and I aquire more brass I can ensure good tension.
 
All good info above, and I'm sure you're on the right track now. I would suggest , however, that once you settle on a neck wall thickness that you like, simply outside-turn your necks to this dimension as they thicken and only use one bushing. And yes...you'll have other bushings you don't use, but may need to again someday with a new batch of brass.
IMHO.
 
Dmay said:
All good info above, and I'm sure you're on the right track now. I would suggest , however, that once you settle on a neck wall thickness that you like, simply outside-turn your necks to this dimension as they thicken and only use one bushing. And yes...you'll have other bushings you don't use, but may need to again someday with a new batch of brass.
IMHO.
Click to expand...
I think Im going to have to, I didnt realize the bushings are $30+ each ! I'll take some time tonight to get measurements from as many cases as I can to get an acurate average, determine the bushing size, then neck turn the cases so they are uniform.
 
Bushings are listed at $10.60 at Sinclairs. Sure some shipping involved, and you'll probly order another $100.00 worth of goodies to make shipping worthwhile, but cheaper than $30.00.:D
 
I should qualify that, $30 each is what wholesale was charging, I havent accually got a price yet from powder keg, he was out of stock and told me to check in on Friday. else I'll just order some from sinclairs, Im sure I can find some other goodies (like a neck turner, hehe)
 
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