The Chamber vs. The Die.....

[hemiford]

Several real good posts lately about resizing difficulties. Has me thinking.

It seems the crux of some of these difficulties is the fact that the "chamber in the barrel"
does not match the "chamber in the die".

So one of those two needs to be modified. Either slightly modify the die,
or slightly re-cut the chamber in the barrel.

If the die matches the chamber, resizing becomes much more problem-free.
Is my thinking correct ?

Either approach would fix the problem.

I'm interested to hear peoples' opinions on which direction they would rather go,
re-chamber the barrel or modify the die ?

 

[MagnumManiac]

I never modify a die in the way you are thinking. I will hone neck sections but that it as far as I go other than matching the expander to the neck. If I need a modification, such as a die that is longer than the base to datum line, and the rifle chamber is minimum, I modify the shell holder to make it shorter by .005"-.010". This is the easiest and cheapest mod to make.

Cheers.

 

[doverpack12]

I would rather try another die than change my chamber or existing die in the 0.2 base region or just below the shoulder. Those are the 2 areas I have seen cause issues, where sizing shorter would not fix and only increased shoulder setback.

Find a die that fits well (Alex Wheeler video) and everything comes together.

 

[Buttermilk]

My chambers are typically cut with a spec reamer. No way I want to modify the chamber, so if anything, the die or shell holder would get modified if needed to fix any issue.

On one chamber, I had to have the die body shortened a few thousands, and on another chamber, I had to takeoff some from the shell holder. One of these was a factory gun, the other was a rechamber that apparently got the reamer ran short by a tad bit.

 

[Beluebow]

It seems the crux of some of these difficulties is the fact that the "chamber in the barrel"
does not match the "chamber in the die".

And this is exactly why everyone that screams don't bump your shoulders back more than .002 doesn't always work. I prefer my brass to drop cleanly on a stripped bolt. Sometimes that requires more than .002 shoulder set back.

 

[Varmint Hunter]

IME, and assuming that the base of the case (near the web) has been reduced enough in diameter, ,002" isn't even needed. I've loaded cases with no reduction in headspace and they fit fine.

 

[Willys]

My typical steps:

1) try different dies
2) sand shellholder
3) hone neck of die
4) polish chamber with 320 flapper to get rid of clickers
5 ) make small base body die by cutting top off regular die.
6) order custom die
7) rechamber with reamer that has matching die available.

 

[VinceMule]

Dies are hardened, 65 Rc is not unusual.

Chamber dimensions are all over the map relating to original reamer dimensions, plus wear, plus chambering techniques. Some guys will chamber with techniques that will cut to exact reamer size, while others will not, the devil is in the details. You can open up chambers with 320 grit with Oil while the barrel is turning in the lathe, it does not go real fast with constantly checking dimensions.

Throw in the fact that there is a tolerance of +/- .0005 from the reamer maker in the grind.

Now throw in different dimensions from various Brass makers.

I am very reluctant to jump onto new offerings due to miss match in reamer, dies, and brass.

These issues can be EXTREMELY expensive to deal with, and it helps to have a machinist background to even know how to analyze the problem with good measuring tools on hand.

I never modify a die in the way you are thinking. I will hone neck sections but that it as far as I go other than matching the expander to the neck. If I need a modification, such as a die that is longer than the base to datum line, and the rifle chamber is minimum, I modify the shell holder to make it shorter by .005"-.010". This is the easiest and cheapest mod to make.

Cheers.

This is great advice.

Where we all get screwed is where the web dimension in the chamber is BARELY over the dimension of New Brass, and this is a goat roping from start to finish, which almost always starts with European brass being used in SAAMI spec Chambers. European brass often should be used in larger CIP spec chambers.

Dies do vary in dimension. Often, a Redding bushing Full-length sizer will vary from a Body die which will vary from a standard Full-length sizer in relation to the dimension in the web. Few reloaders have telescoping gauges or small hole gauges to measure dies nor the experience in how to use them. So, an option is to use Cerrosafe to take a chamber cast of the Full Length sizers which is going off the deep end. Brass has a memory, and brass spring back is always a part of Simple Physics you have to take into account.

Many of our hunting rifles shoot their best just shy of Max pressure. So, knowing how to size and control the dimension at the Web is of major consequences. There are a few gunsmiths out there that really know their business in this issue of dies, web dimension in the chamber with particular brands of brass. These gunsmiths are worth every penny you spend with them. This information on reamer design is proprietary information, and these highly qualified gunsmiths make their living developing quality service,. These gunsmiths do not talk about Reamer/dies/brass except to their paying customers as a rule.

 

[Mikecr]

It seems the crux of some of these difficulties is the fact that the "chamber in the barrel"
does not match the "chamber in the die".

You could generate a list of contributors, but closer to root cause is lack of understanding, leading to lack of planning, leading to tail chasing.
Think about this;
How many people control their chambers? Or their dies?
Have they measured their brass and filled out a reamer print for it?
Does their plan include making brass last, and having enough on-hand for the accurate life of the barrel?
Do they fire form their brass to plan and send some to a die maker for a custom sizing die?

If you merely pick an abstract gun off a rack, and randomly buy dies and ammo components for it, then why would that turn out correct?
You could be lucky, or not..
I have zero luck, so I don't take a lot of chances like that.

 

[VinceMule]

Great post, Mikecr!

Education costs money, Precision reloading is a hobby, seems like we never quit learning. These precision gunsmiths that dedicate themselves to their trade have been a treasure in my life.

 

[hunterbob]

Several real good posts lately about resizing difficulties. Has me thinking.

It seems the crux of some of these difficulties is the fact that the "chamber in the barrel"
does not match the "chamber in the die".

So one of those two needs to be modified. Either slightly modify the die,
or slightly re-cut the chamber in the barrel.

If the die matches the chamber, resizing becomes much more problem-free.
Is my thinking correct ?

Either approach would fix the problem.

I'm interested to hear peoples' opinions on which direction they would rather go,
re-chamber the barrel or modify the die ?

I never modify the die. I will modify the shell holder though. I took a couple 10,000" off one for a 308. Now if you can see in the chamber and it's rough, that deserves polishing. I used crocus cloth on a stick, or and cleaning rod to polish that up.

 

[Doom2]

It seems the crux of some of these difficulties is the fact that the "chamber in the barrel"
does not match the "chamber in the die".

Buy a factory rifle like a 308 or 6..5CM and the chamber will have minimum or larger dimensions based on SAAMi minimum or larger dimensions. Buy a typical Lee, RCBS, Hornady Full Length resizing die and it sizes the brass to something equal to less than the SAAMi maximum cartridge dimensions with a standard shell holder. Change the chamber, change the die, or more commonly change the expectations and problems/difficulties have the potential to arise. Probably most prevalent is trying set the shoulder to an exact dimension or to optimize the neck tension. This is when a custom or specialty customizable die begins to come into play.

Most chamber modifications are centered around neck sizing (die related dimension) or freebore which doesn't affect the die so a full length bushing die can be used. Another option is to use a bump busing die. A bump die aids in optimizing the case datum dimension if the reloader is trying to achieve a specific bump.

If you change the chamber you may well have to change the die also. You can much more easily modify/cutomize a die.

 

[VinceMule]

Standard Forster neck sizers are ALL shoulder bump dies.