Seating depth was driving me nuts

I kept getting differing measurements (from ogive datum to head) resulting from seating (168 SMK 308). Checked the heads for warped rim from extractor damage, et cetera. Didn't seem to be a contributing factor.

Finally, I took a good look at my old Lyman turret (6 position) and determined the main pin that the ram rotates on had a bit of clearance (probably wear) not conducive to repeatable seating depths.

I prick-punched all around the boss at the bottom of the press with the pin installed until it needed to be drifted out with hammer and drive pin. Did the same to the ram block that rides the main pin. I think I got it down to +/- .003 seating depth.

In other words, a micrometer-adjustable seating die would be wasted on this old baby (which was used when I got it). Kind of explains why I've been struggling with accurate shoulder set-back too.

Mo' money.

There probably is another factor involved . . . the actual shape of the bullet ogive.

The seater doesn't push down on the bullet tip (call that Point A) . . . it also doesn't push down on the bullet ogive at the point you use to measure (call that Point C). Instead, it pushes down on some point in between (Point B).

So, if the distance between Points B&C varies from bullet to bullet (and it does), your measurements will vary even if your press seats to what it thinks is the same level every time.

Having just seated 100 175gr Sierra TMKs, those measurements varied within a 0.005" range. My "fix" is this:

Using a micrometer seater I seat each bullet long, measure the cartridge base to bullet ogive, and adjust the micrometer so the second seating will put the bullet's ogive in the right place. I think this is the most important thing to get consistent . . . ie, keeping the jump distance the same . . . once you've gone down this particular rabbit hole :)

I'm doing pretty much as you outlined, except my "micrometer" is using the thread-to-thread math:

7/8x14 tpi die is .0714" thread-to-thread. 1/8th turn (45 degrees)=.009", 15 degrees (3/16" turn) is .003" and 5 degrees (close to 1/16th inch turn) is .001".

The seater and sizing button threads are 28 tpi...twice that of the die body and half the inch values= Full turn .035" (rounded), 1/8th turn (45 degrees)=.0045" rounded, 15 degrees= .0015" rounded.

I did collet-pull too-deep bullets in one group of 50 (just moved them out about .025", not removed them) and re-seated them at .010" short of lands contact.

I have five loads (propellants) which are pretty accurate and am at the point of fine-tuning via jumps.

Thanks! :-)

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Originally Posted by Bang

. . . I did collet-pull too-deep bullets in one group of 50 (just moved them out about .025", not removed them) and re-seated them at .010" short of lands contact. . . .

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Yeah, that happens to me all the time even with the micrometer seaters. I take advantage of the fact that it takes me more than one hit to dislodge a bullet using my kinetic puller LOL. I'm not that good with my collet puller yet.

Collet puller is fast and controllable.

With collet a turn loose, tap the top with a plastic hammer as you introduce the cartridge by applying slight pressure on the ram handle. The bullet will enter the split collet some. Tap the top again once or twice more, the bullet will totally enter and you'll feel the positive stop of the collet contacting the case mouth.

Tighten the collet by hand pressure on the steel rod and give the steel rod a tap with the hammer to further tighten. (If the collet slips without extracting you need to give the rod a bit more tightening). I don't think a collet can damage a bullet by over-tightening, but you'll quickly learn what amount of tightening does the job.

Now, apply slight extracting pressure and smack the ram handle with the hammer and you'll see the bullet incrementally rising from the brass.

Once you get the feel for it, it's a hell of a lot faster and more controllable than the inertia puller.

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Originally Posted by Bang

Collet puller is fast and controllable.
. . .
Once you get the feel for it, it's a hell of a lot faster and more controllable than the inertia puller.

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Especially when you have a bunch to do lol.

Problem is I have only one single stage press, and I'm using it to seat bullets. Maybe 2-3 are too deep out of 100 seated and need to be lengthened. So the inertia puller was my first choice. But maybe if I just put those cartridges aside aside until I'm done . . . worth a try I suppose. Thanks.

Just picked up an older model LEE for 25 bucks at the "Allentown" gun show. I guess it can be described as an "O" frame. It looks like a Challenger type. There seems to be no play in the ram at the top of the stroke. I bolted it to a piece of wood that I can mount on this computer desk with two C clamps. It will be sturdy enough for seating bullets here where I weigh the charges. That will be its only purpose. If I'm right, it should be much easier to achieve more consistent seating depths. (My Dad put this desk together for me when I was a preteen. It would be a stretch to call it furniture, but I don't want/need to drill holes in it).

Quote:

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Originally Posted by Bang

I'm doing pretty much as you outlined, except my "micrometer" is using the thread-to-thread math:

7/8x14 tpi die is .0714" thread-to-thread. 1/8th turn (45 degrees)=.009", 15 degrees (3/16" turn) is .003" and 5 degrees (close to 1/16th inch turn) is .001".

The seater and sizing button threads are 28 tpi...twice that of the die body and half the inch values= Full turn .035" (rounded), 1/8th turn (45 degrees)=.0045" rounded, 15 degrees= .0015" rounded.

I did collet-pull too-deep bullets in one group of 50 (just moved them out about .025", not removed them) and re-seated them at .010" short of lands contact.

I have five loads (propellants) which are pretty accurate and am at the point of fine-tuning via jumps.

Thanks! :-)

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Bang,
thanks for the math above, I've been too lazy to figure this out, often wondered how the incremental turns equate to die /seating depth

I have the same press you use, a nice sturdy press, I will have to check my pins. I also find I have to snug down the center pivot nut on occasion

I've been curious about that center nut and stud. I got to wondering if the stud could be backing out, the threads collapsing, or what. I Lubed the nut-turret surfaces, snugged it and marked the stud and the nut and the nut to turret relationship. When it loosens again, I should be able to figure out what's happening.