A little math can get you in the ballpark very quickly.
Here are the details. (Impatient readers can skip to the summary table at the bottom but please note that table is only correct for standard reloading dies with 14 threads per inch.)
Standard reloading dies are described as 7/8″-14.
The latter number, 14, is the number of threads per inch cut into its sides. What that means is that, if you rotate the die 14 full turns in one direction, it will go down or up exactly one inch.
Each turn, therefore, moves the die up or down 1/14 of an inch. In decimal, that’s 0.071″ or 71 thousandths of an inch.
Unfortunately, that’s way more than we are usually interested in when reloading. Typically, we’re looking for changes of maybe 10 or 15 thousandths, sometimes even less. We need a way of measuring smaller amounts.
Fortunately, there is a smaller division already cut into the die. It’s the adjusting nut on the top.
You’ll notice it has six equal faces. If you rotate the die exactly “one face”, the die will move up or down 1/6th the previous amount: 0.071″ / 6 = 0.012″ or 12 thousandths of an inch.
How we’re getting somewhere!
In the case where we measure an OAL that is 12 thousandths too short, rotating the die’s adjusting nut — not the locknut — “one face” out (counterclockwise) will move the die up that exact amount.
And no doubt you’ll immediately see that rotating the adjusting nut half that amount — I’ll call that a “half-face” — will move the die up or down 6 thousandths, and a “quarter-face” would change it a tiny little 3 thousandths (0.003″).
But before you run to your press, here are a couple more suggestions.
Buy yourself two good quality fixed-jaw wrenches, one 7/8″ and the other 1″. The reason is because, if you’re like me, those lock nuts have become chewed up by loosening and tightening them with poor wrenches.
I love Dillon Precision equipment but, frankly, the little black wrench Dillon ships, because its faces are thin, tends to turn askew and bite into the lock nut. After a while, the lock nuts can become pretty beat up and it may become hard to adjust them.
Worse, the adjustable (crescent) wrenches we all have in the plumbing section of our home toolboxes always have a small amount of “play” in the jaw opening and they will also chew up the lock nut so that, again over time, the lock nuts become harder and harder to work.
If that has already happened on your reloading press, I suggest you do what I did. Buy two wrenches (about $10 each at Sears and yes, they still have “warranted forever” Craftsman hand tools), one for 7/8″ and the other for 1″. And also call Dillon Precision and order five “Dillon Die Lock Ring” nuts at $1.05 each (2012 price) to replace your chewed up ones.
Then, to make the very fine adjustments we’re talking about here, you will need to be able to loosen the lock nut, change the die’s adjustment and then, without moving that, re-tighten the lock nut. That’s why you need two wrenches. This just cannot be done accurately with one.
- First, if you are using the Dillon dies, to get enough clearance for a standard wrench (instead of the skinny one Dillon provides — that eats up the nuts), you’ll need to remove the bullet seater insert by pulling off the locking clip and immediately catching the insert assembly below. This gives you full access to the adjusting nut at the top of the die.
- Now, put the 1″ wrench in place on the lock nut — but don’t turn it yet.
- Next, place the 7/8″ wrench on the adjusting nut and hold it in place while you now loosen the lock nut. A quarter turn should be plenty. In the next step, leave the 1″ wrench in place and hold the lock nut to prevent it from turning.
- Gently remove the 7/8″ wrench without disturbing the adjusting nuts position and manually rotate it the desired amount with your finger tips. (I’ll give you an alternative way to do this in just a moment.)
- Then, put the 7/8″ wrench back on (gently!), hold it in position and tighten the lock nut.
- Lastly, for the Dillon die, reinsert the bullet seater assembly and install the locking clip to hold it in place.
But it gets better!
As an alternative to the hand adjusting of the die, you can make even smaller changes by keeping the 7/8″ wrench in place, but to see how, we need some more math.
What we’re after are “half-face” (30 degrees) and “quarter-face” (15 degree) adjustments. And while I can visually guesstimate a 30 degree turn of the wrench, that’s about my lower limit. Less than that and I need help.
Remember that the circumference of a circle is Pi times the diameter?
In this case, the wrench will form the radius of the circle so we’re going to need to double the wrench’s length to get the diameter of the circle it makes when rotated.
Let’s say you have an 8″ wrench. Imagine you put it on the die and rotate it one full turn. The outer edge of the wrench will make a circle that is 2 * 8″ * 3.14 = 50.24″ in circumference.
That is, the outer end of the wrench will draw a circle about 50″ around.
One sixth (one facet) would then be an arc of 50.24″ / 6 = 8.4″ around.
And that tiny “quarter facet”? That can now be very accurately made by rotating the wrench so its far end moves just about 2″.
How much did the die move up or down for that 2″ (quarter face) adjustment?
If a full face is 0.012″, the a “quarter face” will be 0.003″ (three thousandths).
In reloading, I accept a tolerance of ±0.005″ for the OAL. That “quarter face” adjustment gives me the fine control I need to get there.
But remember there are many variables in reloading. You may not get exactly that 0.003″ change if something else slips in to bite you. Remember the platform that rotates the shells has a slight amount of vertical play and your OAL will be different with one versus five shells in the platform.
And if a bullet is tilted slightly when pressed into the shell, the bullet seater insert may catch it in a slightly different place. Again, that will affect the finished OAL of that round differently from that of others.
So, after any adjustment, it is essential that you make a couple of test rounds and measure them.
Adjust, make and verify. Repeat as needed.
The calculations and adjustments described here will get you “in the ballpark” faster, but remember it’s going to be your hand on the gun when it goes bang.
Adjust, make and verify. Always verify!
Here’s the summary for your reloading room or notebook.
OAL Adjustments: 7/8″-14 Dies Only
Always verify every adjustment!
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