Checking seating pressure.
- Thread starter LorenC
- Start date
The late Dave Dohrmann made and marketed an arbor press setup with a seating pressure gage which used a peizoelectric load cell. Actually, I'm not sure he ever got it into production........??........ I've set up arbor presses to use an inch/lb torque reading wrench. I haven't seen much about it lately.
al
al
adamsgt
Jerry Adams
I would guess that all of can feel when a bullet requires more or less force to seat than the rest of the of the ones we're doing. At that point though, we're left with a primed case full of powder and a seated bullet. So what do we do with it. Disassemble it, use as a sighter? If we shot it, what would we measure it against that would tell us something useful?
K&M has an arbor press with a force measurement option. Here's their description: "The force measuring model measures force by indicating the deflection of a spring pack assembly where one pound of force is equivalent to 0.001" as noted on the dial indicator." The spring assembly is a stack of belleville washers. I have respect for belleville washers as they were used as the spring in the bolt of my Millennium Palma rifle.
I have a K&M arbor press along with others. You can get the force measurement as an add-on and I just may do that. It'll be something to do these long winter months. Another thought came to mind as I was previewing my post. It would be useful if you had an indicator that would preserve the maximum reading obtained. As it is, you would have to note and record the reading while maintaining pressure on the spring pack. I'll bet there are indicators out there that will do that. More time to spend on google.
K&M has an arbor press with a force measurement option. Here's their description: "The force measuring model measures force by indicating the deflection of a spring pack assembly where one pound of force is equivalent to 0.001" as noted on the dial indicator." The spring assembly is a stack of belleville washers. I have respect for belleville washers as they were used as the spring in the bolt of my Millennium Palma rifle.
I have a K&M arbor press along with others. You can get the force measurement as an add-on and I just may do that. It'll be something to do these long winter months. Another thought came to mind as I was previewing my post. It would be useful if you had an indicator that would preserve the maximum reading obtained. As it is, you would have to note and record the reading while maintaining pressure on the spring pack. I'll bet there are indicators out there that will do that. More time to spend on google.
Jerry, This is a very interesting subject, would you please keep us up to date on what you learn during the long winter months.
Thank you,
Dick
One problem with having a tattle tail reading is that when you come to full seat the pressure slightly spikes up. From all my looking so far it seems the K&M is the only one on the market at this time?
As for the seated round that doesn't stack up to the others, setting it aside and grouping it with others with common pressure readings comes to mind first.
As for the seated round that doesn't stack up to the others, setting it aside and grouping it with others with common pressure readings comes to mind first.
Here's another aspect to consider from our friends at accurateshooter.com:
Neck Tension vs. Time
Lesson learned: for match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing.
We've learned that *time* (between neck-sizing and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you'll see dramatic improvements in ES and SD, and your groups will shrink. Typically you'll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how hard the neck grips your bullets.
However, James Phillips recently discovered that another critical factor is at work. He loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases--not even close. Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the "older" cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s. (These numbers correspond to pounds of force applied to the bullet).
Conclusion: In the two weeks that had elapsed since neck-sizing, the necks continued to get tighter and stiffen.
The K&M will spike when seated. I use one for long range and you can tell the difference on the target. i have a loading block that i have color coded rows and i mark the tips of the bullets to correspond to the lbs. in that row and use 2 lb. difference per row and i make sets for my record rounds. It is paying off, but it's work …….. jim
adamsgt
Jerry Adams
Hmmmm, does that mean that the necks shrunk a bit or did the brass get harder? Either one could add to the force required to seat a bullet. Sounds like more experimenting is needed although it sounds like the brass getting harder is the likely culprit. Could already sized down necks shrink further over time, probably not.
Joe and Jerry: After reading the conclusions of our friends at accurateshooter.com, I've changed my habits and plans so that I'm loading and seating either the same day that I size my brass or within a day or two. Waiting an excessive amount of time seems to create a situation where excessive force is required. I'm not in favor of applying excessive force to anything when it comes to reloading. I thought it was an interesting article and the findings worth considering.
adamsgt
Jerry Adams
Thinking about the case neck changing led me to consider how to measure changes. Measuring the OD is no problem, the ID is another matter. My pin gage set runs in .001 increments. That's probably not fine enough. Have to see if there's bore gages that small. There's always Deltronic pins but they're pricey. More stuff to buy. I've got the K&M force measurement add-on coming. I'm sure there's a way to measure pull force but I don't know how to do that yet. Somebody probably does. The gunsmith forum on Practical Machinist might be a good place to pose these measurement method questions.
Boyd Allen
Active member
I have not gone the gauge pin route, but with an outside micrometer and neck thickness micrometer, both reading to .0001, I don't really feel the need. In any case, long ago, I noticed the comparison between the force it took to seat bullets in cases that had just been sized, and those that had been sized a couple of weeks earlier. I thought that it might be something about the grain boundaries of the metal being disturbed and then resetting over time, the new configuration becoming normal. This would not necessarily show up as a dimensional change.
A while back, a friend who was working to wring the most accuracy out of .17 and .20 Ackley Hornets found that getting the neck tension right and very uniform is very important to the accuracy of his ammunition. He worked with expander mandrels polished to very slight variations to find the best tension. A friend of his got into machine annealing as well, for the same calibers. The results were unambiguous. Not only was having the right neck tension important, but uniformity was as well.
I think that as sectional densities increase with caliber and bullet weight, these factors may become less of an issue at more normal ranges, but for the short bullets, in the smallest calibers, bullet pull is a higher percentage of the the resistance that must be overcome and start the bullet into the rifling.
A while back, a friend who was working to wring the most accuracy out of .17 and .20 Ackley Hornets found that getting the neck tension right and very uniform is very important to the accuracy of his ammunition. He worked with expander mandrels polished to very slight variations to find the best tension. A friend of his got into machine annealing as well, for the same calibers. The results were unambiguous. Not only was having the right neck tension important, but uniformity was as well.
I think that as sectional densities increase with caliber and bullet weight, these factors may become less of an issue at more normal ranges, but for the short bullets, in the smallest calibers, bullet pull is a higher percentage of the the resistance that must be overcome and start the bullet into the rifling.
adamsgt
Jerry Adams
My K&M force measurement add-on arrived yesterday. We'll be having nasty weather for the next couple of days so that's a good opportunity to experiment with this new to me tool. There's the old saying about measuring it with a micrometer, marking it with a grease pencil, and then cutting it with an axe. I can measure pretty well but my bench manners are cutting with an axe. I can probably realize better results by focusing on improving my bench manners. That said, I'm still going to play with all this neat stuff. 
I haven't thought this through, but it this true? And if so, why? My knee-jerk is that more percentage jacket=more force required to engrave rifling....
al
Boyd Allen
Active member
That may be a factor as well, but to my thinking, the jacket thickness is more of a constant, and bullet pull a variable.
geo.ulrich
New member
yes....
JerrySharrett
Senile Member
The reason for this change in hardness is that brass is one of the metal alloys that "age harden". Some other metals that age harden. or precipitation harden, if you prefer, are lead alloys that contain antimony, copper and aluminum among a few others.
http://en.wikipedia.org/wiki/Precipitation_hardening
Does neck tension have a significant effect in powder/pressure performance? It is somewhat dependent on factors like amount of bullet jam/jump-if a bullet is jammed hard neck tension does not effect variation in performance as much as a bullet that is jumped. Another factor is the powder itself-example H322 doesn't care as much for startup resistance as does VV133.
Try to break your seating pressures down to simple terms like, light pressure (in a Wilson type seater) the bullet can be seated with thumb pressure, medium pressure the bullet requires you to use the heel of your hand, and hard seating would require the use of an arbor press. Within those groups, now you can "feel" for variations from cartridge to cartridge. And, by all means for best accuracy strive to keep seating pressure constant.