[Unclenick]

Marty,

Welcome to the forum.

The Dillon dies work a little differently than most rifle dies. You have a sizer/decapper/expander die, a seating die, and a separate taper crimp die. On a Dillon press the powder dispensing station goes between the first and second die in the set.

The Dillon seating die instructions appear to be a cut and paste calamity that could cause any newbie total confusion. The first step serves no purpose and should be skipped. The second needs to be modified to just start the die in. I won't go on.

The object of the exercise is to screw the die body in just far enough to align a case, but without interference fit, then to subsequently adjust the seater stem (plug) at the top to press the bullet in to the correct depth. The seating die body does not touch the shell plate the way the sizing die does. The Dillon seating die also does not have a crimp ring built in the way other seater dies do. Crimping is handled by the separate taper crimp die supplied with the set and used in an additional step. That really is better for accuracy as Dillon claims.

To set up the Dillon seating die, work as follows:

1. Back the seating stem (plug with hex head screwed into into the die body) way, way out or remove it completely.

2. Start the die body into the press, but just two or three turns, so it is still way up high.

3. Put a resized case in the shell holder under the die.

4. Run the press ram up (pull the handle down).

5. Now turn the die body in until it is stopped by contact with the case.

6. Now back the die body back out 1/8 of a turn (45°).

7. Now tighten the lock ring on the die body and tighten its set screw.

Congratulations, the die body positioning phase is now complete. On to phase two, the seater stem:

8. Lower the ram by raising the press handle. IF you are using an auto-indexing Dillon press, like the 650 or 1050, do not lower the ram far enough to index. Just far enough slip a bullet in over the case mouth.

9. Place a bullet in the case mouth.

10. While holding the bullet straight, raise the ram all the way up again.

11. Leaving the die body right where it is, screw the seater plug in until it makes firm contact with the bullet.

At this point we will start to control the seating depth. There are a couple of ways you can go about it. One is the iterative approximation, which is a technical term for estimating and trying and nudging until you get there. It's what is used in the Dillon instructions and by most people. The other is by calculation. First the iterative method:

12. Lower the ram a little and screw the plug in one eighth turn.

13. Run the ram all the way up.

14. Lower the ram enough to see how far the bullet has been seated.

15. Repeat 12-14 until the cartridge is the desired COL. Obviously, more than 1/8 turn may be done at a time until the COL gets close. Obviously you can remove and measure the cartridge to check COL as it gets close.

(Sorry. Wife rang the lunch bell. I'll come back and edit the other method in.)

A tip to make step 14. easier:

Take a resized case and trim and chamfer and deburr it. Take a Magic Marker and put a lengthwise stripe on the bullet. Set your caliper to your desired COL. Place the bullet base in the case mouth and hold it aligned as straight as you can. Use the caliper to measure from the case head to the stripe on the bullet and use it to scratch a mark in the Magic Marker stripe. That line is what you want to seat even with the case mouth. It makes a quick way to check progress at step 14. just by looking and without removing and measuring the cartridge.

A point about desired COL. As a beginner, the easiest thing is to ask the bullet maker what COL he intends for his bullet in the .308 cartridge? 2.800" is a maximum for .308/7.62 NATO loaded rounds IF they are to fit in a magazine. Going longer for accuracy is common, but you need to load these too-long-for-magazine rounds singly, and you need to know how far out you can seat before the bullet jams the throat, and you need to adjust the charge for the difference in pressure that results. For a beginner, I would not attempt this until you are comfortable with conventional loading.

Seating shorter than 2.800" is common, particularly with lighter bullets that have shorter ogives. These are designed to be loaded to a shorter COL. The 150 grain Hornady FMJ, for example, is one I use a lot of in .30-06 Garand loads. It is designed to seat until the crimp cannelure is even with the case mouth. In a .308 it will end up at 2.780" COL.


Another way to start

The other adjustment method is to learn how far you want the bullet to seat into the case and figure out the number of turns of the seater stem needed to get there from first solid contact with the bullet (step 11.). This isn't much different from the above at the very end, but it lets you get close a lot faster.

The Dillon dies use 18 TPI threads on the seater stems, so that's 0.0555…" per turn or about 0.007" per eighth of a turn. I put a magic marker line or a scratch mark on my seater stems, then mentally divide a quarter of a turn into 3 parts. That's a 1/12 of a turn or 30°, and is 0.0046", or just under 5 thousandths on the Dillon dies, which is fine enough for bullet seating adjustment. Most bullets vary in length by that much or more out of the box.

Once you know the COL, measure several bullets to find their average length and pick one close to average. Set the bullet in the mouth of a resized case that's ready for loading and measure the total length, holding the bullet as straight in line with the case as you can. From this length, subtract the COL you want. That difference in length is how far the seater will need to press the bullet into the case. We'll call that Added Depth (AD). It is distinct from seating depth, as seating depth includes the depth of a boattail in the case, if your bullet has one. You already had that inside the case mouth during the above measurement, if it does.

The formula is simple:

Turns = AD × 18 (if you're not using Dillon dies and have some other seater stem TPI sub that for the "18" in all these calculations)

That's it. If the difference you got was 0.3 in, then:

0.3 in × 18 turns/in = 5.4 turns deeper are needed after bullet contact is made in step 11.

To get the number of twelfths,

0.4 × 12 = 4.8,

So 5.4 turns is 5 whole turns, plus 4.8 twelfths. 0.2 twelfths is slightly less than a thousandth of an inch, so I would just ignore that and go with 5 twelfths.

If I got that 0.3 in result, I would get to step 11, above, add 5 turns, run the press ram up, then withdraw it and check the COL. I would subtract the desired COL from the new, actual measured length and recalculate a new AD with that number. Assuming it came out the same (it usually won't quite, because there is spring in the case and press). Then I would make the final adjustment to the nearest twelfth from that new AD.

Don't be surprised if you have to nudge the seater stem in a little further for your actual load run, especially if you are using a progressive press. When you seat a cartridge in steps, the bullet usually winds up a little deeper than when you do it all in one stroke because of the spring mentioned. For a progressive press, when one station is simultaneously sizing, another dispensing powder, another seating and another crimping, so there is more flex of the press than when seating one round alone. Often you get cartridges coming out a consistent average length only when all stations are filled. If you are loading for match shooting, figure to set aside for practice the first and the last rounds made when the stations were not filled. Anyway, after final nudging, you can set the lock nut for the seater in place.

Voilá.