gunamonth said:
I can get very repeatable results with the Hornady/SP tool. My technique is just tapping lightly on the end of the rod. As noted you want the bullet to slide freely through the "sample" case.
This is true, as long as you understand that the length is probably meaningless. When you use the Stoney Point/Hornady tool correctly it stops when there is zero headspace which more than likely doesn't represent what happens when you close the bolt of the rifle. I'm convinced that the only way to get an accurate measurement of the base to ogive is by chambering a dummy round with a bullet seated long with minimal neck tension and letting the lands push the bullet back.
Conversely, the measurement one gets with the "tool" is valuable when you chase the lands. The case still stops at the same place so an increase in the "tool" measurement should accurately represent a necessary change in the actual base to ogive of the loaded round.
Gunamonth, while I agree that the tool may not be identically headspaced as a loaded round with fired, sized brass, I would argue that it doesn't really matter--so long as the measurement is repeatable.
What I mean is, if the "just touching" measurement is not actually 0.00" land contact it doesn't really matter so long as you understand that fact. Maybe it is really 0.03" in the lands, but if I can repeat that measurement,and I'm convinced one can), and I can load to that length plus/minus a given number of ten-thousandths, it means that all my ammo has the same rim to ogive length round after round, which is all that matters.,Recognizing that the bullets themselves may be a bit different--which is why I measure base of case to ogive of all my loaded rounds).
The Horn/SP "zero" length is just a starting point. Then you go shoot and see what works. You may find, for example, that Horn/SP tool "zero" + .010" shoots best. Whether that is truly .007" in the lands or .013" doesn't really matter, because that is just a reference baseline.
I have, in front of witnesses and on video, measured length to lands 10 times in a row with the Horn/SP tool and came up with the same length within 0.0015" every time. I believe that while that measurement may not be "absolute", it is certainly not meaningless. It gives me a repeatable reference of bullet to barrel contact length that I can use to determine where to position the bullet.
Conversely, we have done tests with the method of "soft seating" long and closing the bolt, and honestly we found that way of measuring was MUCH LESS REPEATABLE at least with long bullets. Some times the bullet would engage in the lands, engrave itself a little and stick a bit,yielding a longer length), while other times it would push back more,yielding a shorter length). This is particularly true with long VLD type bullets. It helps to lubricate the bullet, but we still found we could not repeat the measurement within .003" ten times in a row. And sometimes the measurement was way off when the bullet engraved a lot. Neck tension is obviously critical with this procedure too.
As with everything, YMMV. If you prefer your method that's fine as you have probably learned to control it. Some people say it works better if you remove ejector and firing pin. But I've recently worked with some new reloaders who were advised by others to use the seat long/close bolt method. They were frustrated because they could not get repeatable measurements with long bullets. When we switched them to using the SP tool at least they could repeat their measurement 5 times in a row. This gave them confidence that they had something solid to start with. Then they can work up a seating depth relative to that baseline.
Whether the Horn/SP tool OAL to lands measurement is "relative" or "absolute" I really don't care, as long as it is repeatable. I'm convinced it can be and I haven't found another method yet that is more repeatable.
I know how they are supposed to work.
