One factor that would almost certainly change the resized inside case neck diameter required in order to maximize case neck tension would be the case neck wall thickness. Which can vary greatly depending on how much outside neck turning/truing may have been applied to the case neck. I would venture to say that the greater the case neck wall thickness, the more that additional resizing of the case neck (case neck diameter reduction) would increase case neck tension.
Whether or not one exceeds the yield strength of the brass in the case neck is dependent on the yield (in tension) strength (units of lbs) of the brass, and the cross-sectional area of the brass case neck (units of square inches) exposed to that tensile force. This cross-sectional area will clearly vary dependent on the length of the case neck, the depth the bullet is seated into the case neck (partially or through the entire length of case neck), and lastly, the thickness of the brass case neck wall in the contact area with the seated bullet.
These three pertinent cartridge case neck criteria affect the case neck tensile force required to exceed the tensile yield strength of the brass case neck. These just serve as examples of why I stated, I think it's more complicated than that.
I'll try to experiment with one of my ultrasonically cleaned cartridge cases tonight, because the higher coefficient of friction with one of these cases should exhibit additional bullet pulling force, compared to a lubricated case neck, under added neck tension. Although I have to add, my opinion is a by-product of my prior experiences prepping cases, seating bullets, and pulling bullets. And then trying to gauge the necessity of resizing the necks again prior to seating a bullet in the cartridge case the second time, based exclusively on the press handle resistance to seating/pulling the bullet the second time around.
Last edited by phorwath; 06-23-2010 at 08:19 PM.
Reason: clarification of criteria affecting cross-sectional area
Well, I did the experiment; a single 30-06 twice fired case, FL sized with RCBS and neck sized with a Lee Collet, a 170 gr. flat point .308 bullet and a Forster collet puller.
Basically, I found what I expected. There was no detecetable difference after seating, pulling, seating, pulling, three times each after starting with both sizers and then repeating the test two more times. I don't have a spring scale strong enoght to actually measure the pull force but my arm sure couldn't tell any difference.
I also measured the sized, loaded and pulled neck diameter after each step as nearly as possible at the same point. Before seating the first time, the FL die was tighter by the common 3 thou and the Lee Collet by about 1.5 thou. That's about what I've previously measured on several cartridges in .22, .24, 27, .28 and .30 calibers.
After pulling the first time from each sizer, the neck drew back about .7-.8 thou, or as close as my ability to measure in tenths can tell. After reseating the bullet the neck grew about the same, again within my ability to read tenths. It sure didn't get bigger during the pulling-reseating process!
Again, I found NO detectable force difference in pulling the bullet for any of the three efforts with two dies, six pulls in all, and all with the same bullet and case. And, again, after the first time, the difference in seated and pulled neck diameter averaged only a tad over .7 thou of change, which is what I've seen before and why I said excessively small necks make no significant difference in actual bullet pull. A smaller neck just stretches as it has to and stays where it can stay.
My experiment was with one case only. Because I obtained the same result as I have over the past 5 years doing basically the same thing. With the exception that I don't normally measure inner case neck ID as a tool to determine whether or not I should resize the case neck after pulling a bullet - prior to re-seating it.
I had two loaded cartridges with excessive powder charges, based on the result of firing one similarly loaded one last weekend.
30.06 Lapua brass necked down and fire-formed to .280 RCBS Impproved. Cases are uniformly outside neck-turned with a K&M Services outside neck turning tool.
Bullet is .284 - 160 gr Nosler Accubond.
I use a 0.311" Redding Neck Bushing to size the necks on this cartridge, and I measured the inside neck diameter (ID) of two of my prepped, but unprimed, cases at ~0.2812", best as I could with a 0.001" Mitutoyo dial caliper.
I pulled the bullet on one of these two loaded cartridges. Measured the inside neck diameter at ~0.2822", again best as I could determine. Obviously estimating the location of the needle between 0.282 and 0.283. I noted the force required on my press handle.
Reseated the bullet in the same case noting the force on the RCBS press handle to seat the bullet to the same depth within 0.001" from case head to ogive. Pulled the bullet and noted slightly reduced force to pull the bullet the second time compared to the first. The pulling force was clearly less the first 1/2 of the way and then pretty similar for the last 1/2 of the bullet removal throw of the press handle. I re-measured the ID of the case neck and estimated it to be ~0.0001 to 0.0002" larger than after the first pulling of the bullet.
Reseated the bullet, pulled it. Less force to seat the bullet this time and less force to pull it.
Reseated the bullet a third time and after some initial resistance, the press handle slipped through my fingers and the weight of the handle alone seated the bullet to total depth. Surprised me, as this would not have happened either of the first two times I seated the bullet. The force on the press handle was very notably less to seat the bullet this third time than either of the two prior times. Pulled the bullet and the force to pull was definitely less than that required to pull the bullet the initial time. I remeasured the ID of the case neck after the third pulling of the bullet at ~0.2828 to 0.2829".
I noted that this case had previously been fired following ultrasonic cleaning, so the inner case neck was already carbon fouled. The bullet had been seated in this cartridge case for 2 weeks. Since the inner case neck was carbon fouled, I doubt there was significant chemical bonding of the bullet to brass case neck over that two-week time period.
I don't normally measure the case neck ID for comparison after pulling bullets. Only did so this time since you had done so. I decide whether or not to resize the case neck based on the my feel of the reduced force on the press handle required to re-seat and re-pull a bullet. The neck on this case will be resized with the 0.311" neck bushing, prior to recharging with 1/2 less grain of powder and seating the bullet for final firing.
Don't know what to tell you. The thinner the case neck walls - the more likely your argument holds water. The thicker the case neck walls - the less likely your theory holds water. That's my opinion. Also, I don't know what caliber bullet you're loading. The large the caliber, the greater the surface area contact between the bullet and the case neck for equivalent bullet seating depths. This could affect the ability to feel the difference in force on the press handle? It will have some impact, but not sure in which direction. I don't fine tune and fuss much with the reloading any rifle cartridges less than 7mm caliber. Mostly 7mm, .308, and .338s. I own other calibers, but don't fine tune loads for those rifles, involving pulling bullets during the load development and refinement process.
Our experiments reached different conclusions. My result was the same as I've previously experienced with 7mm and .308 caliber cartridges. I am certain that my inner case neck ID grew over the four bullet pulls and three bullet seatings. By a minimum of 0.0003" even when I round my estimated neck ID measurements in the direction to minimize the difference between the first and last measurement.
Pretty sure we've reached differing opinions on this topic also. I have no grief over that, and hope the same for you.
"Reseated the bullet a third time and after some initial resistance, the press handle slipped through my fingers and the weight of the handle alone seated the bullet to total depth. Surprised me,..'
Surprises me too..Ain't no way the weight of my RC II's handle could seat the bullet on the third seating. Nor was the third pulling any easier. And the ending neck diameter was within some .0002"(I really can't use a micrometer on neck differences that tiny very well) of the same diameter as after the first pulling.
I don't have a RC II, so don't know what you've got for a handle on your reloading press - longer/shorter or lighter/heavier. Mine's the original RCBS RC press with a heafty solid steel handle. I applied force to begin the third seating of the bullet and then the weight of the handle alone completed the seating when the handle slipped through my fingers. I was holding it lightly in the effort to sense the muscle force applied to the handle.
Each consecutive pulling and seating of my bullet seemed to require less force. But by the third time, comparing the first to the third, the reduced force on the handle couldn't be denied.
Are you stating that your third bullet pull case neck diameter was within .0002" of your first bullet pull case neck diameter, and that you were unable to determine if it was .0002" smaller or larger than the initial measurement? Not sure what you're stating.
I measured the inner case neck ID following each of the four bullet pulls, but only provided the first and last measurements, because I agree the ability to define 0.0001 is a challenge. On my dial caliper, 0.0003" is just about 1/3 of the distance between the 0.001" calibration marks, and it's not very difficult to estimate "greater than 1/3" or "less than 1/3" of the distance between the 0.001" calibration lines. Which is why I presented the difference between the initial and final measurements, after the combined total measurement difference exceeded 0.0003", rather than try to reach any conclusion following 0.0001" incremental increases. Just as with the force on the press handle, the difference between the inside case neck diameter measurements from the first bullet pull to the fourth bullet pull could not be denied.
Yes, my findings more or less duplicate my prior experiences, except I've never measured case neck OD or ID in the past, as an effort to document changes in diameter with subsequent bullet seating and pulling cycles.
Based on our experiences and experiment, seems like the logical course of action is for you to reseat pulled bullets without bothering to resize the case neck prior to reseating. And for me to resize prior to reseating.
Last edited by phorwath; 06-24-2010 at 04:18 PM.
Reason: Misinterpretation of boomtube's post - my bad
"I don't have a RC II, so don't know what you've got for a handle on your reloading press - longer/shorter or lighter/heavier. Mine's the original RCBS RC press"
Only difference between your Rock Chucker and mine is that your lever has a green bicycle grip while mine has a black hard plastic ball, meaning my lever is likely a little bit heavier than your's.
I'm sure I will continue to neck size any pulled cases with a Lee Collet neck die. All of the previous was written to tell the OP it's really not necessary, not to defend what I do as the gold standard for others.