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Topic: Bullet Seating Force Gage ruminations (Read 265 times) previous topic - next topic

Bullet Seating Force Gage ruminations

I've been buried in a lot of non-gun stuff for what seems like forever but, I've not lost sight of instrumenting the bullet seating phase we all deal with.

From the last time I posted, progress has been made.

Measuring force and distance was previously limited to about 50 samples per second which is not bad but, considering the entire seating operation takes about 1 second, the sample rate limit was an incentive to stretch the operation. The sensors, and interfaces I'm using now have a sample rate of around 120 per second. The result is more granular tracking of the seating stroke without trying hard to time-meter the stoke, and the cost increase for the improved performance is less than a box of factory hunting rounds.

It's either been said by someone famous, or maybe I made it up but, the best way to improve software is to force the programmer to use it; I've used it, a lot. I feel the program, once the important settings are understood, is recording and presenting accurate information.

Anyway, figured I'd share a reloading session from earlier today where I tried to make the best ammo I could, and recorded it.

5x fired 6.5 Creedmoor Lapua brass, body sized and bumped 0.002", neck sized with a Lee collet die.

Necks 2x treated with Neolube, first application allowed to dry, then a second application.

Hornady 140 gr BTHP bullets seated 33 OTL.

LE Wilson micrometer seating die with an instrumented K&M Precision arbor press.

Here's a screenshot of the seating curves:

The X-axis shows ticks, each tick represents 0.01 millimeters or about four ten thousands of an inch. The total seating distance is about 0.27". The Y-axis shows force in pounds.

This group of 20 seatings doesn't surprise me with it's consistency; that's what two applications of a neck lubricant seems to do in my limited experience. The first phase, up to about 560 ticks covers the insertion of the bullet into the neck and, patting myself on the back, indicates the hand loader got his neck tension down quite well, dissention and disagreements are welcomed of course :).

The second phase between 560 and 960 ticks shows a divergence of seating forces which spans about 10lbs. I don't know what that means but, I can say with certainty, not one of these strokes called attention to itself, I simply felt no difference from 1 through 20.

The force trend after 960 ticks seems to dip slightly, then the brick wall hits with the die being fully compressed. I don't know how much stock I put in the last, tiny bit of movement and force, it's an infinitesimal amount of movement with a dramatic increase in force. Do some seatings really put up a fight at the ragged end or, are we at the resolution limits of the instrument? I'm inclined to believe the latter until experience indicates otherwise.

I'm going to shoot these, record the metrics and the target which I'll share. I've marked the cartridges in order to directly relate them to their seating force curve. Fun stuff!


Re: Bullet Seating Force Gage ruminations

Reply #1
Very well done chris.. the gradual rise in the graph would be expected i would think as more bearing surface enters the neck.. i have a question.. is the boat tail and bearing surface junction below the neck and shoulder junction ?

Re: Bullet Seating Force Gage ruminations

Reply #2
👋  i have another question.. lol. Did you measure the rounds after you seated the bullets.. just curious how consistent the seating depth on them are..

Re: Bullet Seating Force Gage ruminations

Reply #3
I'd like to see a "turd thrown in the punch bowl" not lubing a case would be too obvious. Can you run a few with different neck tension to compare with a sample treated the same as these?

Re: Bullet Seating Force Gage ruminations

Reply #4
Good questions Grant, the bearing surface is right before the neck-shoulder junction last time I looked, I'll get a to-scale picture tomorrow to confirm. I'll do the same for the seating depths. I did seat 6 rounds outside this to start with, those all measured the same for seating depth using a Mitutoyo caliper.

Re: Bullet Seating Force Gage ruminations

Reply #5
The reason i asked was because alot of bullets has a slightly larger ring around them just as the bearing surface starts.. i thought that might be where the slight drop off at the end of the graph was coming from if that ring was going past the neck and shoulder junction..

Re: Bullet Seating Force Gage ruminations

Reply #6
I'd like to see a "turd thrown in the punch bowl" not lubing a case would be too obvious. Can you run a few with different neck tension to compare with a sample treated the same as these?

I'll endeavor to try what you suggested Dave. This time around I wanted to free myself from the machine and just do it, let the chips fall. I'm a pretty good turd launcher, we'll see how the machine deals with it :)

Re: Bullet Seating Force Gage ruminations

Reply #7
Here's what the seating looks like Grant. The picture makes it look as if the bullet noses are not lined up, they really are, just that the unseated bullet is below the seated one.

Re: Bullet Seating Force Gage ruminations

Reply #8
Chris looking at that picture the pressure ring on the bullet may be just starting to go into the neck where it starts to grow into the shoulder.. im thinking that is the reason for the slight drop in seating force there at the end of the graph.. one way to find out would be to seat one .030 longer and see if the graph keeps climbing into the big spike at the end

Re: Bullet Seating Force Gage ruminations

Reply #9
If you make the graph bigger it looks like some flatline, some dip and some get a slight increase. I understand you're thinking Grant and I don't disagree with you but I'm of the opinion that they're not all exactly the same no matter how hard we try so they're not all going to seat the same. One example would not make a test so a whole set would need seated long to identify a trend but again they're still not all exactly alike so I bet they would still vary before the pressure spike.

Even with the 21st Century Hydro press I find myself relying more on the feel and no matter the trouble taken to make them the same some feel different in spite of the dampening of the hydraulic load cell.
I don't plan on getting rid of it but if it broke tomorrow I'd dust off my old Sinclair arbor press and carry on.

The genius of Chris's work here is it can be examined bit by bit and a person could sort them any way imaginable and test them to see if it does make a difference where with my hydro press I can watch the needle or go by the feel and tell when ones different but it definitely takes a bigger more noticeable variation for my eye or feel to notice and process it.

When I seat bullets and sort into the box I start in the far upper right corner with the ones that feel right and fill in down that row until full and work my way left. Any obvious outliers go to the far left for barrel warmer/ foulers.
I'm sorting for seating depth to the exact .000 at the same time no +/- so even a half a thou off keeps it out of the right 4 rows of the box.

I don't chase the seater, the bullets have been sorted B to O and OAL so if they don't seat the same something is off, neck tension? lube? BS/pressure ring diameter etc. for whatever reason it's different a seating depth correction doesn't make it the same IMO so they get shot as early siters.

Ideally the right 4 rows fill up quickly and from there the other perfect rounds start filling in at from the second row from the left going right 4 rows across the top and fill downward from there. My turds are in the far left row and then something off on seating depth ends up in the bottom 2 rows and the top 3 rows in the sister side of the are the go to "trust your last siter" rounds.

I know that got long and possibly confusing but measuring seating depth aside Chris's tool could bring that process from feel to fact and a guy could truly tell how tight the pressure variance has to be, identify it and sort accordingly.


Re: Bullet Seating Force Gage ruminations

Reply #10
Dave, how are you "controlling" the neck tension or inside carbon deposits
to make them all the same. If one case has just a bit more or less carbon in the neck
or .0005 more tension, wouldn't that make the feel different?
I know you've said you use pin gauges to measure the ID.
Now Chris uses a graph mixture to lube the inside of the case, as well
as that is, I would think that could make it too slippery to accurately measure
a big difference in neck tension.
I could be wrong, just posing a question.

Re: Bullet Seating Force Gage ruminations

Reply #11
Below is a picture which magnifies the area at the end of the stroke. The vertical red line seen just past 1060 is where I arbitrarily set the upper distance constraint for computing useful work. What I've been doing is marking this point when about 30lbs of force is being applied to the fully compressed die. Obviously, a very small amount of movement is possible when 250lbs of force is applied, not to put too fine of a point on it but, the actual distance travelled after the red line in the most extreme case was 0.00787402", lol. I may re-think my 30lb constraint factor.

Anyway, back in the real world, I created the Force Gage Viewer so that post-seating review of the collected data is possible. It supports hovering the mouse over a particular curve at any point which then shows the force, distance and the curve name at that point. From there, a right-click in the list for any curve turns on markers for the curve making it easier to see it amongst the noise. It also allows the graph axes to be changed creating a zoom effect if interest lies in a particular area.

Force curve 10 is the one that looks the most like an "outlier" to me. It got "tight" about 0.02" before the red line whereas the rest of the group got "tight" about 0.01" from the red line. As I mentioned in the original post, I couldn't feel the difference. No matter, I'm going to shoot FC10 as the last shot of group two, let the chips fall where they may this time around.


Re: Bullet Seating Force Gage ruminations

Reply #12
@Ranger 188

After turning and initial fire forming I pin gage them to find any thicker / thinner necks.

I prep with a tight enough rotary brush, not exact but I feel it has the best chance to get anything out of the necks or at least make them closer to the same. Again seating "feel" is my main culling tool.

Re: Bullet Seating Force Gage ruminations

Reply #13
I think I have proof that reloading requires a sense of humor, lol.

I shot the 20 rounds yesterday which were the subject of this thread. The range was blessed by a healthy left-right crosswind, otherwise it was a pleasant day weather-wise. After negotiating Labradar transmit frequencies with several other shooters, we all managed to stay out of each others way.

The Force Gage and Velocity figures shown below are screenshots where the velocity numbers are in a spreadsheet overlaid by the force curve graphs.

Let the comedy show begin :)

The ES for the entire group of 20 shots is 53fps with an SD of 12.5. I decided to take the two most extreme velocity shots to see where they land on the graph. FC-13 was the slowest at 2794fps, FC-7 was the fastest at 2847fps. I turned on markers for both of those force curves in order to see how their bullets seated. Wait for it...wait for it...the two curves, while not identical, are so close even the most jaded eye would not sort them into different piles.

Starting from the graph instead of the velocity data, I took a look at the two most diverse curves; the one I said previously was the most likely "outlier", FC-10, and FC-1 which is the flattest curve, more or less. Again, they're both marked in the picture. FC-10 has a velocity of 2818fps, FC-1 has a velocity of 2807, a spread of 11fps. I'd be OK at this stage of my game if I could consistently put up an ES of 11fps.

Velocity isn't everything of course, just another metric. Still, seeing the two most different seating curve shots have pretty close velocities, and the two most extreme velocities have very similar seating curves, doesn't indicate a high degree of correlation, not for this limited experiment anyway.

I wish I'd had a way to associate the target with the shots but I did not. The groups are there but the individual shots are not. The target is posted below, not my best day but, cherry-picking is not how I roll. Ignore the center target please, it was a warm up with some left over stuff. The one I pulled on 3rd target was funny; the guy next to me yelled to his buddy right as I was pulling the trigger, so loud it startled me, lol.


Re: Bullet Seating Force Gage ruminations

Reply #14
I shot my 6.5 prc so bad today i pulled all the rounds i had loaded for it down and starting over.. 😁

Sad thing is at a 100 yards it was shooting one ragged hole groups.. at 250 yards they were 2 inch groups.. lol