how to set up dies

H

holl

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I have a custom barrelled 300 win mag. It is a hunting rifle and I am want to full length resize so the rounds will chamber easily. I'm using lee dies set up to full length resize. Winchester brass and fairly hot loads. I have had problems seating bullets on about the 5th firing. I feel resistance to seating and the shoulder "swells" right at the shoulder/body junction. These rounds won't chamber because of a ring around the case in this area. My best guess is that i've created a donut in the neck shoulder area and the bullet hit it when seating and collapse the case.
How do you set up the belted mags dies for resizing so the case doesn't stretch?
 
Treat the 300 Mag. as you would a non belted rimless round, set your dies to size with only .001 or 002 of shoulder set back.
Belted magnums are supposed to headspace on the belt and if you are setting your die as recommended by most die manufacturers, against the shellholder, you may be setting the shoulder back much further than necessary. I'm surprised that your cases aren't seperating ahead of the web, but possibly the belt causes the case to stretch nearer to the shoulder. Section a case and it will be evident where the streatching is taking place, there will be a visible ring where the brass is thinner.
I have measured a lot of new Win. 300 Mag cases with an RCBS comparator and typically an unfired case is .007 to .010 shorter to the shoulder than a fired case.
A simple but slow method is to back your die .030 off the shellholder and size the case, if it goes into the chamber screw the die in slightly approx. 1/4 turn and try again with a different fired case. Keep doing this till the sized brass does not chamber, at that point your full length sizing has caused the shoulder to move forward.
Continue sizing a different case each time then adjusting the die down till the cartridge chambers with the bolt handle going down snugly but not with excessive force needed. You are now headspacing on the shoulder as all good cartridges should.
The use of the same case repeatedly to achive this will give you a false headspace. The previously sized case will not spring your press as much as the unsized case and if you set your die with it then size a not previously sized case it will be to long to chamber. After you set your die properly go back and size all your previously sized cases as well as the unsized cases.

Hope this helps.
 
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After reading my previous post, written after midnight, I have decided to amend my procecure.
Back the die more than .030 off the shellholder to start, try around .100.
When screwing in the die on successive sizings only go 1/8 turn or less.
This will be slower but more accurate.
 
How to set up dies

The problem may lie in the seater die instead of the sizing die. I'm not sure about the Lee die, but most factory hunting caliber seating dies have a reduced diameter in the upper part of the neck to allow crimping into a bullet that has a groove for crimping the case mouth into. From the description of the problem, it sounds like the cases are growing in length as you fire and resize them and when they get long enough, you are trying to crimp into a bullet not set up for crimping.
Two ways to solve this. You can back out the seating die where it wont try to crimp, even at max case length. Another way would be to trim the overall length to where you don't encounter the problem. Personally, I would set the sizing die up to not crimp on the maximum cartridge length and monitor the case length and when close to max, trim to .010" under max.
 
I agree with riflemeister. Check your case length. It sounds like your bullet seater die is hitting the mouth of the case and causing the shoulders to spread. If your cases are within allowable tolerances, back your seater die up. You'll have to extend the seater to get the same OAL.
Even if you have to trim your cases, it wouldn't hurt to back your seatr die up a bit if you're that close.
 
The problem is in the sizing. (the seating die is adjusted to not come anywhere near a crimp, bullets are seated long) I worked on adjusting the sizing die for less sizing. Now it is neck sizing only. I'm going to inside neck ream next firing. On the loading that was giving the problem, I remember seating some bullets with a normal smooth stroke of the press handle. Other started smooth and then got hard. I think that was a thicker part of the neck that caused the soft brass to collapse around the shoulder.
 
I think you need someone more experienced to have a look at what is going on .
 
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Holl,

It sounds like you may be describing 2 different problems. Without seeing your cases and your chamber, it's hard to say for sure, but here is what I'd look at first.

Problem 1

You've probably already done this, but it needs to be mentioned. Clean and examine your chamber and the inside of your dies. Then use a bore brush to clean the inside of both, and also use the bore brush to clean the inside of your case necks.

Problem 2

Measure the width of all of your cases just above the belt using your calipers. Use the flat edge (not the knife edge) of your calipers to take this measurement. This area measures .507" on a new unfired case, and none of them should exceed .511"

Take a look at my website at www.larrywillis.com to find more information about reloading belted magnum calibers.

- Innovative
 
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