Sizing Bottle Neck Rifle Cases

[JFrank]

Maverick

 

[Bc'z]

Brett Maverick

Now he had SWAGGER

 

[divingin]

Can someone explain how the shoulder gets bumped .001" or .002" by screwing the die down a fraction of a turn when the die is already touching the shellholder at the end of the press stroke?

If you set the die to touch the shellholder without a case, then size a case, the press will flex or stretch a slight amount due to the friction of driving the case into the die. The result of the stretch is that, when sizing, the die no longer touches the shellholder at full stroke. By setting the die lower, it overcomes the stretch of the press, allowing you to bump the shoulder back.

Lots of variables here - the amount of force needed to size your case is a big one, the rigidity of your press, etc.

Pretty easy to verify, though: Set up as above, then run a case in and either use a light to look for a gap between die and shellholder, or see if a feeler gauge now fits.

If you were talking about the die touching when sizing a case and still being able to increase the bump by screwing the die in further, then I don't know.

 

[Richard Coody]

Can a fl bushing die be set to size the necks only for the first 2 or 3 firings so you can get a fully formed brass? Or are you just bumping the brass back every time even after just the first firing.

Thanks

it is simple to size the neck without bumping the shoulder with any full length sizing die.

back the die off until when you cycle the ram it doesn't touch the neck at all. then screw the die in in small increments and cycle the ram. if you look at.the neck of the brass you will see the portion that has been sized. continue to make small adjustments, cycle the ram and watch the neck. when most.of.the neck is sized but before you get to the shoulder stop. lock your die and size the rest.of.your brass.

one caviate. cycle that first sized case in your rifle. sometimes sizing the case body can make the base to shoulder datum measurement longer. at that point it is time to set up the shoulder bump.

 

[Bart B.]

Full length sizing setting case shoulders back 1 or 2 thousandths was proved best for accuracy in the late1950's.

Couple years thereafter, removing expander balls then honing out die necks to 1 or 2 thousands smaller than loaded round neck diameter put the icing on the accuracy cake.

 

[XTBAR]

Unless the same reamer is used to cut the chamber and FL size die, your guessing.
This is the idea behind Forster making bushing bump dies. They neck size only, but can bump the shoulder back when necessary, without squeezing the case wall down.

 

[Bart B.]

Unless the same reamer is used to cut the chamber and FL size die, your guessing.

Why would anyone do this?

How does such a die size fired cases from such a chamber?

 

[Puzzaz01]

Why would anyone do this?

How does such a die size fired cases from such a chamber?

I'm right there with you. I can't see how a sizing die cut from a chambering reamer having the ability to reduce/size down a fired case. They would be the same size. Why not just stick the case back in the chamber and cycle the bolt a few times? I can understand how one might bump the shoulder back but no way in hell size the diameter of the fired brass. If I'm wrong, please enlighten me.

Darrin

 

[Dusty Stevens]

I'm right there with you. I can't see how a sizing die cut from a chambering reamer having the ability to reduce/size down a fired case. They would be the same size. Why not just stick the case back in the chamber and cycle the bolt a few times? I can understand how one might bump the shoulder back but no way in hell size the diameter of the fired brass. If I'm wrong, please enlighten me.

Darrin

They dont. They pretty much decap the brass

 

[XTBAR]

They can bump the shoulder, and have bushings to control neck tension. Unless you run a semi-auto, or are pushing pressure for that next node, FL sizing is not needed. Certainly not on every firing.

Neck size only dies are readily available as are bushing/bump dies. They have worked, and still do. Holding the fired case very close to chamber dimensions.

If you know your exact chamber dimensions, and have a FL die that is say, .002 smaller, you might have something to make more consistent ammunition, but if you have a random factory chamber, and a random RCBS or whomever die, I don't believe FL sizing is going to help your accuracy or brass life.

Also, if you fire a round in your chamber, extract that casing and cannot rechamber that fired casing smoothly into the chamber it was fired in, with a bolt action, your FL die is masking bigger problems. Shoulder bump I understand, but full length sizing in a general sense, is counter productive in my experience, but I'm no professional and only a hobbyist. I'm sure that I could be wrong.

 

[Bart B.]

Neck size only dies are readily available as are bushing/bump dies. They have worked, and still do. Holding the fired case very close to chamber dimensions.

Neck only sizing dies don't align case necks well centered against the case shoulder, on those headspacing on their shoulder, when fired. The case shoulder is what centers the case neck and bullet in the chamber. Everything forward if the shoulder touches nothing on perfectly straight rounds: save the bullet ogive if seated long to push back when chambered.

Cases bodies with a few thousandths clearance to chamber will fit very repeatable in the chamber when fired. They don't lay in the chamber bottom when fired.

 

[JFrank]

Just to put things in perspective a course human hair .0015

 

[rwj]

Neck only sizing dies don't align case necks well centered against the case shoulder, on those headspacing on their shoulder, when fired. The case shoulder is what centers the case neck and bullet in the chamber.

The Redding Competition Neck Sizing dies have a spring loaded insert that centers the case using the shoulder before the bushing contacts the neck.

 

[Bart B.]

The Redding Competition Neck Sizing dies have a spring loaded insert that centers the case using the shoulder before the bushing contacts the neck.

If the bushing has a zero tolerance diameter fit (press fit) to its place in the die, that might work if case bodies are not too much out of round.

Their FL bushing dies' have clearance.

 

[Bart B.]

If you know your exact chamber dimensions, and have a FL die that is say, .002 smaller, you might have something to make more consistent ammunition, but if you have a random factory chamber, and a random RCBS or whomever die, I don't believe FL sizing is going to help your accuracy or brass life.

Near 50 or 60 reloads with such cases from stock RCBS honed out dies bumping shoulders. 002", one shooting all shots in 3/8 MOA at 100 in SAAMI spec chambers doesn't mean anything?

 

[Howland]

Just to put things in perspective a course human hair .0015

I must have fat hair, mine is 0.0177".