Setting shoulder bump for 308win

[jkgts1]

[JackEllis]

*If* they fit in the chamber *and* it's a bolt gun, I'd neck size only or at most, set the die to bump the shoulder to 1.623.

I shoot two different .223 bolt guns. For both of them I started with a piece of brass that would NOT chamber in either one, then bumped the shoulder until it chambered in both guns comfortably. That's now my comparator reference.

[baih777]

Do you have any factory ammo to measure ?

[FLIGHT762]

Are you depriming the fired brass before measuring? With the Hornady comparator, you can get false readings from a fired primer that has cratered a tiny bit. That will throw measurements off.

Also, not using enough case lube can cause shoulder bumping inconsistency and running the case too fast In / out of the die. Make a slight pause at the top.

To see what easily chambers in your rifle, you can make some dummy rounds @ .623", .622" & .621". Chamber them and see when you start to get a crush fit. You may find that the .623" will chamber. That will let you know at what shoulder measurement you will get sticky chambering.

You won't hurt your brass going to .621". As long as you're not bumping past .005", your brass will last fine.

[Mesa Defense]

Are you depriming the fired brass before measuring? With the Hornady comparator, you can get false readings from a fired primer that has cratered a tiny bit. That will throw measurements off.



Also, not using enough case lube can cause shoulder bumping inconsistency and running the case too fast In / out of the die. Make a slight pause at the top.



To see what easily chambers in your rifle, you can make some dummy rounds @ .623", .622" & .621". Chamber them and see when you start to get a crush fit. You may find that the .623" will chamber. That will let you know at what shoulder measurement you will get sticky chambering.



You won't hurt your brass going to .621". As long as you're not bumping past .005", your brass will last fine.

+1...

[JackEllis]

You won't hurt your brass going to .621". As long as you're not bumping past .005", your brass will last fine.

I reload mostly used brass and my limited experience thus far suggests cases will likely fail at the mouth rather than at the web, and it'll happen when you size your brass, not when you fire it. I have a pie pan with about 8 .243 cases where the mouths show signs of pretty extreme work hardening. They cracked or came apart right after being sized.

[jkgts1]

[pacrat]

Thanks for all the hints everyone. Yes I did pop the primers out on the brass with a dedicated decapping die. Have not sized them yet because I was trying to figure out why they are not tight in the chamber after firing.

The reason they are not TIGHT, is a phenomenon known as "spring back".

The case is expanded by internal pressure during firing. Until it completely fills the chamber. But immediately after firing. When the bullet clears the muzzle and internal pressure equalizes with external ambient. It springs back from the chamber wall.

If it didn't. You would need to beat on the ejector rod of a six shot DA revolver with a rock to eject all 6 cases.

[smoothy8500]

The Hornady "comparator" is not a perfect measuring tool but allows you to get a relative number (since 308 Win headspace GO is 1.630"). Set your Full Length die for .002" less than your fired cases. Stick with FL dies, since neck sizing will eventually require a full sizing after approximately 4 firings anyways.

[jkgts1]

The reason they are not TIGHT, is a phenomenon known as "spring back".

The case is expanded by internal pressure during firing. Until it completely fills the chamber. But immediately after firing. When the bullet clears the muzzle and internal pressure equalizes with external ambient. It springs back from the chamber wall.

If it didn't. You would need to beat on the ejector rod of a six shot DA revolver with a rock to eject all 6 cases.

Yeah that's what I was thinking. Thanks.

[jkgts1]

The Hornady "comparator" is not a perfect measuring tool but allows you to get a relative number (since 308 Win headspace GO is 1.630"). Set your Full Length die for .002" less than your fired cases. Stick with FL dies, since neck sizing will eventually require a full sizing after approximately 4 firings anyways.

Yep I understand that 0.001" is very small and it wont be perfect, thanks for the help

[jkgts1]

Okay so I ran into something else, haha. The fire formed brass I've been measuring have not been run through any sizing dies, because my under standing is that this will give a close representation of what the chamber looks like. The brass was not tight in the chamber what so ever in this form. So, I decided to run a case through the sizing die, with the decapper pin taken out. I'm guessing this just resizing the body of the case. I set the die up to manufacturers instructions. I'm using a Dillon 550 with Dillon dies. So, the case grew 0.002" after this, which I can understand. Metal is being moved its gotta go somewhere type of thing.

So, now I have a case that is snug in chamber after I've run it through the die. After sizing it came out to 1.627". So, is it accurate to start with this piece of brass to figure out my die setup and shoulder bump? Or is it not a good representation of the chamber because I resized the body?

Thanks

[sofbak]

Well, you should make one more case measurement before adjusting your die. That would be over all case length. You want to be sure the "snug" fit you're observing is at the datum diameter and not the case mouth.

[baih777]

Okay so I ran into something else, haha. The fire formed brass I've been measuring have not been run through any sizing dies, because my under standing is that this will give a close representation of what the chamber looks like. The brass was not tight in the chamber what so ever in this form. So, I decided to run a case through the sizing die, with the decapper pin taken out. I'm guessing this just resizing the body of the case. I set the die up to manufacturers instructions. I'm using a Dillon 550 with Dillon dies. So, the case grew 0.002" after this, which I can understand. Metal is being moved its gotta go somewhere type of thing.

So, now I have a case that is snug in chamber after I've run it through the die. After sizing it came out to 1.627". So, is it accurate to start with this piece of brass to figure out my die setup and shoulder bump? Or is it not a good representation of the chamber because I resized the body?

Thanks

See if this brass will chamber in your rifle.
Make sure the bolt closes without sticking.

[divingin]

The brass was not tight in the chamber what so ever in this form. So, I decided to run a case through the sizing die, with the decapper pin taken out. I'm guessing this just resizing the body of the case.

Assuming you have a full length, non-bushing type sizing die (standard sizing die), removing the decapping pin (which also has the expander ball attached to it) will size the body of the case normally and bump the shoulder back if set up to do so, but will also size the neck quite a bit smaller than desired. That type of die is designed to size the neck smaller than desired, then on the press handle upstroke, the expander opens the neck back up to the desired diameter. There may also be some possibility that the shoulder changes geometry slightly due to the resistance of the expander being dragged up through the neck (at least in theory - I've never checked.)

FWIW, in my bolt rifles (the plural is intentional), it may take 2, 3, or more firings on a piece of brass before it gets tight on chambering. The springback is kind of iffy, so different pieces of brass react differently. Some from the same lot may get tight after the second loading, others may go 5 or 6 times.

To set your die up, you can do the following:
Take and reserve a single piece of brass. Load and fire. see if the fired brass chambers without resistance. If it does, back your sizing die out a full turn (so you are not moving the shoulder at all, just part of the neck), load and fire again. Repeat until the fired case causes resistance on bolt closure. At that point, the case base to shoulder is too long. Measure the case base to datum with your Hornady tool and subtract a thousandth or so, and that should be the max you can have before your cases cause chambering problems. (You can also measure after each firing, and use that to determine the too-long measurement by estimating what portion of the last firing change you need to get back to a good length.)

Now slowly screw the die back in, checking the CBTD after each adjustment. When the CBTD reads about .002" smaller than the measurement that dragged (or matches the measurement you determined above), and you should be good to go. Sizing all your cases with that setup should ensure that the shoulder is bumped enough to chamber in your rifle (not necessarily for any other rifle though.)

There's other stuff that may affect that as well: If the case body requires a lot of sizing, that will push the shoulder higher. If your case lubing is inconsistent, it will cause odd results from differing friction forces applied to the press, die, and case. Lots of other things as well, but you get the idea.