Modified case from Fired Brass

[rlandry6]

Ae there any amateur(or professional machinists on here? I would like to have modified cases out of fired cases for my Hornady Comparator. I understand the Hornady cases will get you close, probably close enough, but the measurements you get from it are relative. it would be nice to know the actual head space dimension and know exactly how much you're bumping the shoulder when you need to FL size. I would probably be willing to donate the drill and tap so that others could benefit from a little more accuracy out of their rifles. Any thoughts?

[rebel]

My method is fairly accurate if I don't have a modified case. Clean the case and run it into the die until just a bit of the neck is sized. Sharpie your bullet and load it long. Chamber and close bolt. It's real easy to see the rifling.

[bangbangping]

My method is fairly accurate if I don't have a modified case. Clean the case and run it into the die until just a bit of the neck is sized. Sharpie your bullet and load it long. Chamber and close bolt. It's real easy to see the rifling.

That works. I've had trouble with the bullet pulling out some when extracting, so added a little super glue in the case mouth. You do have to work fast.

But a case isn't hard to make even without a lathe. You just need a way to hold the case. My method:
1. Drill a hole the size of the case head (or a tad smaller) a few inches from the end of a piece of soft wood. I use whatever scrap is handy, somewhere around 1" thick and 2" wide.
2. Cut a slot from the end of the board to the hole.
3. Optionally apply a little rosin and insert the case. Clamp the end of the board to grip the case.
4. Drill out the primer hole in steps. If you try to drill in one go the case will likely spin.
5. Tap with a 5/16-36 while still clamped in the board. That's not a common tap and the big box won't have it, but they can be found on Amazon. https://www.amazon.com/16-UNEF-Machine- ... B01N4PSBA8

[ozleux]

Just to expand on Rebel's method, which I think works a little better than a Hornady gauge

https://www.youtube.com/watch?v=TWmIwPwLyyg

[rlandry6]

That's a great video. My only question...
He says size a case so that it goes in the chamber. Would it not be more precise to use a case that had been fired in that rifle so you would know what the headspace actually is and bump the shoulder back a couple of thousandths? That way you know exactly how far off the lands the bullet is going to be when your loaded rounds are chambered.. Then you could use the comparator o measure the case head to ogive and set your seating die to seat to that dimension.. Just thinking out loud.

[bangbangping]

That's a great video. My only question...
He says size a case so that it goes in the chamber. Would it not be more precise to use a case that had been fired in that rifle so you would know what the headspace actually is and bump the shoulder back a couple of thousandths? That way you know exactly how far off the lands the bullet is going to be when your loaded rounds are chambered.. Then you could use the comparator o measure the case head to ogive and set your seating die to seat to that dimension.. Just thinking out loud.

It doesn't matter with this method because the length is determined by the bullet in the lands on one end and the case head against the bolt face on the other.

On the other hand, that measurement you oh so carefully take to the .0005" will put you into the lands once you load a resized a case and reinstall the ejector. I would also argue that you could slightly deform the bullet pushing it into the lands multiple times. Likely enough so that measuring to the half a thou is pointless. No two bullets are identical, either, and since you're mating the tapered lands with the tapered curve of the bullet, "touching the lands" is a range, not a precise measurement that is absolutely identical from round to round. People get too worked up over meaningless precision sometimes.

[rebel]

The other method I like, folks don't seem to do as much, more math maybe?
Seat a bullet in a case prepared as before, with enough slip so that the bullet will move inside the case. Seat it and take an appropriate sized dowel and run it down the barrel to contact the bullet. Mark dowel. Remove bullet and run the dowel down to bolt face. Mark dowel. Measure those marks - OAL. Reseat dummy bullet to that length and measure CBTO.
As bang said, bullets are not perfect and vary from lot to lot or even through the same box. These methods get you close.

[golfindia]

^^^^ That's how I do it. I cut a slit in a master case with a dremmel. Very gently push into chamber then poke it out with a dewey rod. Even if you don't do all the math, you get a max point of reference.

[dellet]

Ae there any amateur(or professional machinists on here? I would like to have modified cases out of fired cases for my Hornady Comparator. I understand the Hornady cases will get you close, probably close enough, but the measurements you get from it are relative. it would be nice to know the actual head space dimension and know exactly how much you're bumping the shoulder when you need to FL size. I would probably be willing to donate the drill and tap so that others could benefit from a little more accuracy out of their rifles. Any thoughts?

I have been trying to understand this question since it was posted and still don’t get it.

If you want to know actual headspace, bolt face to datum line, you will have to measure it. There is no easy way to do that for the average hand loader. The easiest way is to start with a piece of brass that is sized too long at the shoulder, keep bumping the shoulder until it fits then measure.

Or you can put a piece of brass in the chamber and measure the movement with a dial indicator.

Knowing the headspace dimension, and knowing how far you are bumping the shoulder back are two completely separate things.

You can know how far you are moving the shoulder, without knowing what the headspace is.

Deciding how much to move it, is generally relative to the size of the case is is after firing and how it will be chambered. The brass stretches then shrinks slightly after firing, the idea is to keep that stretch to a minimum.

So the advantage of using a fired case that is base to datum as you will use it to determine where the bullet will hit the lands has merit.

What I do is seat a bullet long in a case sized as I will use it, set the rifle muzzle up and slide an inert round into the chamber with finger pressure. The round will quit sticking in the lands when the shoulder contacts the chamber. I use a set of Redding competition shell holders to move the bullet .002" at a time.

Using the same shell holders you can move the shoulder .002" without touching the die and can determine the headspace with the bolt closing method if you want to strip the springs.

[Omega]

If you want accurate measurements, you can get the actual measurements by casting your chamber with cerrosafe, or you can do a pound cast. But it's easier to get useable measurements with the hornady tool.