Neck Tension vs Bullet Seating & Release Pressure - Lessons Learned

[ButterBean]

'Bullet Pull' is a term useful only for recoil seating concerns.
It's purely frictional, which is different and separate from neck tension

Regardless, we all know what he saying and comprehend it no matter how it's worded

 

[243winxb]

https://apps.dtic.mil/sti/citations/AD0862734

When the bullet starts to move on primer firing, is most important. To soon is not good.
Slow burn rate powder in large magnum rounds do not do well.
Secondary pressure spike on firing , not good.

On autos, the action of loading a round may increase cartridge COL. Loose bullet hold. Low pull pounds.

 

[243winxb]

SAAMI-
NECK TENSION
The circumferential stress that the case neck exerts on the seated bullet, as a result of the interference fit provided by the case neck inside diameter and the bullet outside diameter.

BULLET PULL
The force required to extract a bullet from the case into which it was loaded.


More neck tension increases bullet pull?

 

[ButterBean]

SAAMI-
NECK TENSION
The circumferential stress that the case neck exerts on the seated bullet, as a result of the interference fit provided by the case neck inside diameter and the bullet outside diameter.

BULLET PULL
The force required to extract a bullet from the case into which it was loaded.


More neck tension increases bullet pull?

Say it ain't so

 

[cajun]

A lot of f class guys use an arbor press with force seating gauge when seating bullets. Anything high or low out the norm are set aside and not used in the match. While seating force might not be the same as release pressure it's really the only thing you can measure.

 

[ButterBean]

A lot of f class guys use an arbor press with force seating gauge when seating bullets. Anything high or low out the norm are set aside and not used in the match. While seating force might not be the same as release pressure it's really the only thing you can measure.

How do you figure that's the only thing you can measure ?

Mecmesin | Bullet extraction and seating force testing

Requirement When making ammunition, the projectile is set into the casing and it is crimped or sealed in place. The "neck" of the cartridge has natural tension but the crimp/sealant does the bulk of the work in keeping the projectile in place. It sets the minimum force needed to extract the...

www.mecmesin.com

BULLET PULL TESTER

TEHNICAL DATA: The device has PLC and HMI touchscreen monitor with a software which determines the value of each tested bullet and calculates max/...

www.zpvpro.com

 

[Hondo64d]

INTRODUCTION:

I recently completed an experiment that I thought many of you might have an interest in reviewing. After reading many of the posts on LRH (https://www.longrangehunting.com/threads/mandrel-as-last-step.258463/) and Hammertime (https://hammerbullets.boards.net/thread/3557/hammer-bullets-pressure-velocity), I wanted to further examine the seating pressure changes associated with setting different degrees of neck tension (NT) with bushings and mandrels, as well as evaluating the differences between standard cup and core bullets and Hammer Bullets (solid copper bullets with driving bands). In addition, I was also interested in measuring the frictional pressures required to cause these bullets to release from case necks, and how this would also change with neck tension. However, equipment to measure bullet release pressure was not available to my knowledge. Following discussions with "kneedeep" on Hammertime, I was able to devise a simple system with relatively common reloading equipment that would allow measurement of bullet friction release pressure vs neck tension, and I have described this set-up in detail. In addition to findings related to seating and release pressure, some other interesting observations regarding amount of neck reduction vs brass elastic and plastic deformation and maximum achievable neck tension also surfaced. Neck Tension and maximum achievable tension prior to brass plastic deformation due to bullet seating has been a controversial topic on these forums, so hopefully this information may contribute to the discussion. Although I am a scientist, I am not an engineer or metallurgist, so please excuse any incorrect wording or assumptions.



EQUIPMENT & MATERIALS:

• K&M Arbor Press with standard force pack and Mitutoyo dial indicator (0.001" ~ 1 lb of force; max = 150 lbs)
• K&M hollow die base
• LE Wilson Case Holder (H&H Magnum size) to hold cartridge body concentrically to and in-line with the press ram movement
• Lee Shell Holder (#2) to hold base of cartridge and prevent the cartridge from slipping into the case holder
• 0.200" Binding Bolt as bullet plunger

• Cases: Hornady Factory 6mm CM ELD-M 108 gr Match Ammo once fired cases
• Bullets:
  • Hornady ELDM 6mm 108 gr
    • Bullet OAL: 1.2625"
    • Bearing Surface Diameter: 0.2430" over entire bearing surface
    • Bearing Surface Length: 0.4000"
    • Cartridge OAL: 2.7350" (allowing bearing surface to extend to base of neck) (See Pic)
  • Absolute Hammer 6mm 87 gr
    • Bullet OAL: 1.1665"
    • Bullet Max Diameter: 0.2430"
    • Overall Bearing Surface Length of driving band section: 0.3000"
    • Cartridge OAL: 2.7000" (allowing bearing surface to extend to base of neck) (See Pic)

CASE PREPARATION:

• All cases were once-fired, processed the same, and only used ONCE for testing
• The cases were cleaned
• Primer pocket drilled out with 13/64 (0.203") drill bit
• Shoulder bumped with a Whidden FL bushing die with 0.267" bushing in place to allow neck turning
• Trimmed to 1.9130" OAL
• Case mouths were inside chamfered with a VLD chamfer
• Necks expanded with K&M 0.24340" mandrel
• Necks turned to 0.01320" thickness for consistency (0.0142 - 0.0162" prior to turning)
• Necks were inside brushed
• The necks then had a K&M 0.24340" mandrel passed through them again to iron out any potential burs or irregularities
• The cases were felt to be very similar and consistent at this time
• The cases were selected and numbered, with 2 cases being used for each test group (total of 28 cases)

TESTING PROCEDURE (See accompanying images and pictures):

• The selected bushing size (Column B) was then placed in the Whidden FL bushing die, and 2 cases were sized
• The OD of the case neck after sizing was measured and recorded (Column F)
• The chosen bullet (Column A) was then seated using an LE Wilson in-line die on the K&M indicator arbor press with pressure slowly applied to advance the ram and seat the bullet
• A slow motion video was used to video the process and allow careful playback to visualize the ram movement, the range of seating pressures, and the peak pressure
• The range of seating pressures and peak were recorded (Column I), and the neck OD of the seated round was also recored (Column G)
• The case and seated bullet then had a Lee shell holder placed over the extractor groove to support the case, and then the case was inserted into the LE Wilson case holder.
• This combination was set bullet down atop the K&M die base with a bored-out center to allow unrestricted passage of the bullet and case neck.
• The plunger was then inserted through the hole drilled into the bottom of the case until it contacted the base of the bullet (Effort was made to ensure that the plunger was centered on the bullet base and parallel with the bullet and ram movement as much as possible)
• This combination was then placed under the K&M indicator arbor press ram, and the ram was slowly lowered, exerting pressure against the bullet base until the bullet released completely from the case
• Again, a slow motion video was taken of the process to allow careful and slow playback, so the exact point of release and peak pressure could be visualized
• This point of peak bullet release pressure was recored (Column J), as was the neck OD following bullet release (Column K).
• This process was continued and recorded for each size bushing (0.269, 0.268, 0.267, 0.266, 0.265, 0.264), using 2 cases per test.
• In the final test sample, the case was reduced with a 0.264" bushing and then expanded back up with a 0.24105" mandrel.
• Then the process and results were recorded as above.

LIMITATIONS:

• Equipment: I felt that the testing pressures were pushing the arbor press itself, as well as the force gauge, to near its limits (150 lbs). I believe this was limiting its accuracy in measurements over about 100 lbs, leading to potential inconsistencies with data. In addition, maintaining consistent press ram movement and speed was difficult, and also likely introduced error. (I was unable to use my 21st Century Hydro-Press as the maximum allowable pressure (100 lbs) was exceeded by several tested samples.)
• Data: There was a limited number of data points (2) for each test, which was insufficient to ensure repeatability and accuracy.

THOUGHTS & DISCUSSION:

I feel that limitations due to available equipment, time, and sample number, make interpretation of the data limited to general observations and trends. I used a K&M force gauge indicator and manual operation of an arbor press to obtain pressure measurements. Since I was not able to generate curves with the equipment utilized, I used slow-motion video to record the seating and release process to allow review of the video to determine exact seating and release pressures and peak pressures as shown on the indicator. Further, some observations were more apparent during the process than appear from viewing the table. Where these observations were noted and were they appear appropriate, I made additional comments. However, due to the limitations mentioned, I have tried not to over interpret the findings, and have included all raw data for anyone to review and comment upon. In addition, hopefully, this set up and preliminary information will lead to further experimentation and progress in the area as felt necessary. Finally, I do strongly believe that the use an AMP Press, which uses a consistent electronic ram and precisely graphs pressure vs distance curves, would greatly add to the precision and accuracy of the data generated, and would make its interpretation significantly more conclusive.



FINDINGS:



GENERAL FINDINGS:

• I was surprised by the amount of force required to move bullets once seated. Even bullets seated with 0.0005" NT required 35 - 64 lbs of force to move. This increased rapidly up to maximum amount of 140 lbs at only 0.002". Therefore, thoughts regarding the need for heavy NT to prevent bullet movement in magazines and otherwise may be overestimated and may not require more than 0.002", at least in 6mm and with these components.
• As expected, once the bullet began to release, it was an all or nothing event due to the hand pressure exerted on the press handle. An AMP Press may have been able to distinguish partial, incomplete, or progressive movement.
• When the bullets were examined after seating and then releasing the bullets, I was surprised to see that there was no damage or even scratches left on the bullet bases or jackets no matter what bushing and NT was used. This was true for both the Hornady (see image) and AH bullets. This can likely be attributed in large part to the use of a VLD chamfer tool, brushing of the necks, and possibly the use of a mandrel to "iron out" the necks following neck turning. (No lube, graphite, moly, etc was used.) This is important, as it is believed that any damage to the bullet base or jacket during seating will have an effect on short and long range accuracy and precision due to effects on such things as bore seal, bullet release at the barrel crown, bullet concentricity, and BC.

DIFFERENCES BETWEEN CONVENTIONAL BULLETS AND HAMMER BULLETS:

• As expected, compared with the Hornady ELDM bullets, the Absolute Hammer bullets had reduced seating pressures (ave of total: 41.8 vs 60.7) and release pressures (59.6 vs 90.9) under the same conditions. This is almost assuredly due to the fact that the AH bullets driving bands have less surface contact area with the case neck than traditional bullets with a full diameter along their entire bearing surface. One interesting point is that the driving bands can be seen causing undulations in the neck of the brass once seated, so I was not sure if the brass "moving inward" between the bands would effect frictional pressures. However, if there was any effect, it does not overcome the frictional reduction due to reduced surface contact area.
• As expected and while observing the indicator, as each driving band of the AH bullets entered the case neck, the seating pressure did increase in a discrete fashion (ie. 0-10 lbs -> 10-20 lbs -> 20-30 lbs), whereas, the Hornady bullets had a more gradual and progressive increase in seating pressure. There was some movement noted in both bullets even from the beginning of ram contact with the seating die (~ 0-2 lbs). This may be due to the significant boat tail design of both bullets gradually causing the expansion of the necks during bullet seating. I have noted that flat base bullets have more of an abrupt start at a higher pressure in previous seating operations.

NECK REDUCTION & EXPANSION VS ELASTIC AND PLASTIC BRASS DEFORMATION:

• It was very interesting to me that for the Hornady bullets (standard cup and core bullets) maximum seating pressure (Column I) continued to increase with bushing size reduction as expected. However, maximum release force (Column J) was achieved with a NT of only 0.002", after which point it fell to lower levels, and remained at lower levels or at least did not increase over that maximum point. This was even more apparent when operating the press than it appears in the table. This suggests that this may be the final point (with this brass, caliber, and conditions), after which elastic deformation is overcome and plastic deformation occurs, resulting in no further increase in NT after this point is exceeded. The finding that the neck OD after bullet pulling (Column K) also reached a maximum spring back of 0.001" (0.268 vs 0.269") at this same bushing size and beyond may further support this finding. Further, this may confirm what has been suggested by others (ie. Mikecr in LRH discussion on NT and mandrel use) regarding reaching a peak amount of neck reduction after which point the bullet acts an expansion mandrel and plastically deforms the neck, essentially resulting in a fixed maximum NT beyond this point which is dictated by the elastic properties of the brass. This would be important to confirm because it may suggest that at or around a specific neck reduction (0.002" in this case), a maximum tension can be expected, and anything past this point only results in overworking of brass. However, this appears contradictory to findings of others who report that as neck tension is increased from near 0 to as much 0.006", differences in accuracy, velocity, and precision continue to be found. It is possible that each system may have a different maximum elastic limit at which plastic deformation occurs, and that this may be due to caliber, neck thickness, brass composition, brass hardening, bullet composition and material, and other factors.
• The exact same trend was not seen with the AH bullets, although there may have been a slight reduction in release pressure after 0.003". It is not clear if this was related to the reduced overall pressure required for release of these bullets or if it was due to the background noise and reduced sample size.
• It is also not clear to me why a certain degree of fixed neck expansion to 0.269" after Hornady bullet seating and release was found with 0.0005 - 0.001" NT, which was finally overcome after increasing NT at and beyond 0.002" (and thus leading to a spring back of 0.001" with a final OD of 0.268"), but this was not seen with the AH bullets under similar conditions. Hypothetically, this may be due to a "ripple" effect of the driving bands moving across the brass in the neck of the case causing an ironing-like or massage-like effect that moved the brass into its final OD size of 0.2690 for all cases. Some of this variance may also be due to the limitations of my calipers 0.0005" resolution.
• It is apparent that no matter the degree of neck reduction, once a bullet is seated and then removed, the case neck appears to have been plastically deformed back to near its fully loaded size (0.2680-0.2690" OD) (Column K), and does not spring back to its pre-seating OD/ID to any significant amount. This again supports the suggestions and reports that seated bullets will act as mandrels and plastically deform reduced necks back to or near to bullet diameter ID.
• In two experiments, the neck was reduced with a 0.264" bushing, and then expanded with a 0.24105" mandrel prior to seating and releasing the bullet. This resulted in a sized OD of 0.2670", which is the same as a case sized with a 0.266" bushing alone (Column F). Seating and release pressures were then compared between these groups. With regards to using a mandrel to set neck tension, it appears that by reducing the neck to smaller than the desired size and then expanding it back to the final desired size with a mandrel, the neck exerts more tension on the bullet during seating and release, than if reduced to same ID/OD by reduction with a bushing alone and without expansion. (This was seen for the AH bullets for both seating and release pressure, and the Hornady bullets for seating pressure. It was not shown for the Hornady bullets for release pressure. This again may be due to noise and limited sample size.) This is likely due to the inwardly directed spring back of elastic forces generated by the final expansion step, as opposed to the outwardly directed spring back of elastic forces generated if the last step was reduction with a bushing. (ie. with expansion, the brass wants to elastically return inward to its prior position creating additional force; while with reduction, the brass wants to elastically return outward to its prior position reducing force.) This additional force due to the elastic nature of the brass and direction of last movement adds to the force gripping the bullet. However, this can not be measured by OD/ID measurements alone, as these measurements are the same for both treatment groups and represent the resting state of the neck diameter. Subjectively, I also feel that with large enough test samples, setting the final NT with a mandrel will likely be shown to result in more consistent neck tension and seating and release pressures.

NECK TENSION AND POWDER BURN:

• It is not clear how much effect neck tension and bullet release pressure, measured as friction created by a linear force placed on the base of bullet, will have to do with powder burn efficiency and consistency, and overall accuracy and precision. It has been shown that for powder to burn efficiently and consistently, a certain amount of pressure must be built up prior to release of the bullet down the bore. This pressure build can be affected by the inertia required to be overcome to start bullet movement, bullet contact with the lands, neck brass properties, powder and primer properties, barrel properties, and case neck tension and bullet friction. The relevance of neck tension in this process has been brought into question in many discussions, as the case neck is blown out to chamber neck diameter within milliseconds of powder ignition, thus freely releasing the bullet. However, I do feel that NT must play at least an initial role in this process as pressure must build up within the case sufficiently enough to expand the case neck prior to bullet release. This may occur in only a fraction of a millisecond, however it will occur and will be affected by bullet friction and bullet movement. Additionally, many others in all disciplines have reported effects of NT changes on accuracy, consistency, and velocity. I was not able to test the effects of these changes on accuracy and velocity as the cases were modified and could no longer hold a primer or powder. However, cases fully loaded in parallel under similar conditions could be tested for accuracy and velocity and would likely provide additional useful information.
• Finally, it is not clear if the reduced neck friction noted in the AH Bullets (solid bullets with driving bands) compared with standard cup and core bullets results in any loss of consistency and / or efficiency in powder combustion, and if so, can this be improved by increasing neck friction. I must admit that I have had great results with regard to accuracy and velocity the Hammer Bullets, but can it be even better? Since it does not appear possible to significantly increase bullet friction for Hammer bullets with NT alone, are other options available? Several members of both forums (ie. butterbean and shinbone) have done extensive work in this area, and have reported that crimping Hammer bullets in the case neck can improve both velocity and accuracy. Presumably, this would be due to increased combustion pressures prior to bullet release. I have not experimented in this direction yet, but this is another interesting area to explore.

I hope this adds some new ideas and new information to the field, and provides a good source of further discussion. Also, if anyone has an AMP press and would like to perform similar experiments, the above described set-up can be employed without the need for significant machining or modifications. Mike D.

Very well done. Have you tested to see what difference the neck tensions make in group size on the target?

John

 

[DoneNOut]

Very well done. Have you tested to see what difference the neck tensions make in group size on the target?

John

I'm no physimachist, but I gave it a shot: PUN INTENDED!

Here we go...

Background:

Right out the gate I screwed this whole experiment by not loading the same recipe back to back .002 & .004 neck tension, but I think regardless we can come to a conclusion and get "other value" from this range session. I was excited about load developing 137HH with TAC and N135 and that right there was more than enough to sidetrack my squirrel brain! My apologies.

Today's Range Session:

Murphy knew I was excited too. He latched onto me today and tried his best to turn my time into a waste. Once again, I detected his *** and made the corrections to his shenanigans. I switched my rear bag rider to a 20oz heavy steel version to balance out the rifle. I forgot I only did a soft seat of the bag rider and it came loose. I shot most the groups before realizing this too. Also, I had to recover from the anxiety of thinking I just completely lost all my skill at shooting small groups!



Setup - I typically like to test loads from a full supported bagged position as photo illustrated. Then I move to slow fire bipod, and then after I have a knat's *** load, I take it to the drag strip and see how it holds up with 10 shot rapid prone bipod. I set my zero to this result of the rapid prone position and consider development over and onto ringing steel at distance. I've gotten pretty freakin good at the bipod position lately. Because going back to the Bull's bag turned me into a football bat. (Reference TAC group 48gr) My technique changes with the bipod shooting and there is a zero change as well. I took hard note of this and I will no longer be using the Bull's bag for load development, but rather everything starts slow fire prone bipod.



Due to the fact I struggled with the adversity of the loose bag rider I gave myself liberty to take measurement of the best 3 shot groups. Totally admitting experimenter bias here As you can see, TAC was a nightmare with ES/SD, but it shot pretty daggum good regardless. There is a combustion problem, but not a tuning problem here: (Will .004 NT help this?)



I've never had primers look so good after firing! Look at the mostly rounded primer edges! 49gr load even came out looking pretty! Very impressive MV too.


The N135 showing gobbs of promise! Less felt recoil as well. 3000fps really is my accepted velocity out of this 20". No sense in beating up my rifle and brass chasing velocity. Here is when I discovered my bag rider problem. I got to shoot two groups with it tightened and I began to recognize myself on paper again.



"If I didn't have bad luck, I would have no luck at all!" Just when I got my bag rider sussed out, my most accurate group teetered into over pressure on one round. Blew the pocket on the case head with red arrow. Won't duplicate this charge weight again. I do, however, think I can shoot the 43.5gr loading much better with a tight bag rider and off my bipod. Maybe get to 3000fps with 43.7gr? (I will always want to drop at least a grain from an overpressure charge weight)



These were all fired with .002" NT. Previously I had .004" NT and got similar groups. So I ask myself, "With @mrdinpoli results from his experiment, and my results from this range session, what is the point of increased NT?" Then I remembered all my 155gr & 168gr Amax loads shot wonderful with .002" NT: (I settled on that NT just from smooth seating feel of bullet and results on paper long before MrD's experiment, so I accidentally did something right! LOL



Other thoughts:

What is the crimp doing? Can we set .002 NT and add some "crimp insurance" to build dwell time pressure? Or is the crimp unnecessary? I personally like the little kiss crimp into a PDR band because it looks sexy AF in pictures. Sometimes that is enough for me! Bwahahaha! Combined with the case neck outside chamfer & PDR groove crimp, "Oh Honey, Shush!



Does alternating shooting the Amax and Hammers have any affect/effect on group size? Holes punched in paper with Hammers look cleaner than the dark holes punched by Amaxs.

Powders successful to date with 137HH: IMR4895, IMR3031, AA2520, N135, TAC. (And the Devil's powder LeverEvolution. Assigned moniker another story)

Again, is there a point to going over .002 NT if all we are doing is working the brass more for no more release tension?

My 6mm Bergers in .243 AI with .002 NT bug holes. 6mm 88gr Hammers at .004 & crimped bug holes.

NEXT:

43.7gr N135 137HH at .002 & .004 NT
49gr TAC 137HH at .002 & .004 NT
49.5gr TAC .002 NT

 

[sestamibi]

A lot of f class guys use an arbor press with force seating gauge when seating bullets. Anything high or low out the norm are set aside and not used in the match. While seating force might not be the same as release pressure it's really the only thing you can measure.

I have certainly done this, but also before I even get to bullet seating, I use a expander mandrel. If there is a significant variation in the force used to expand the neck, that case is culled.

 

[sestamibi]

If you really want to adjust tension, you need to vary sizing LENGTH.
This because tension (neck grip) is in PSI. So adjusting area of the spring back grip (force applied) adjusts tension.

So I am curious how practical it is to adjust neck tension by varying the length of the neck being sized. How would someone precisely adjust this on sizing die or a neck die? For me, if the bushing "rattles" a little when I shake the die, I call it good. But I believe that Redding makes a die specifically for adjusting the length of the neck being sized. Also, LE Wilson states that their neck dies only sizes the neck to 3/16" from the mouth end.
Thoughts?

 

[cajun]

How do you figure that's the only thing you can measure ?

Mecmesin | Bullet extraction and seating force testing

Requirement When making ammunition, the projectile is set into the casing and it is crimped or sealed in place. The "neck" of the cartridge has natural tension but the crimp/sealant does the bulk of the work in keeping the projectile in place. It sets the minimum force needed to extract the...

www.mecmesin.com

BULLET PULL TESTER

TEHNICAL DATA: The device has PLC and HMI touchscreen monitor with a software which determines the value of each tested bullet and calculates max/...

www.zpvpro.com

Let me rephrase that. The only practical way. Seating a bullet then pulling it only to have to size it again and reseat it would be a pain and some of that equipment is pricey. Not to mention once you seat the bullet again who knows where you are. Looking at seating force is easy to do and throwing out the oddballs can limit potential flyers.

 

[ickes123]

I Have no idea what the heck mrdinapoli said but impressed

 

[Mikecr]

So I am curious how practical it is to adjust neck tension by varying the length of the neck being sized. How would someone precisely adjust this on sizing die or a neck die? For me, if the bushing "rattles" a little when I shake the die, I call it good. But I believe that Redding makes a die specifically for adjusting the length of the neck being sized. Also, LE Wilson states that their neck dies only the sizes the neck to 3/16" from the mouth end.
Thoughts?

I use Wilson hand dies for all neck sizing. I can adjust neck sizing length to exactly any value within the range of bushing thickness.
I imagine pretty much any bushing neck die can be adjusted in sizing length, with some able to exceed bushing thickness. But I can't picture a benefit in sizing that much length of any neck. We should keep in mind that the greater the tension, the greater the variances of it.
It seems to me that if you need an extreme NT to get a good powder burn, then you're likely using the wrong powder.

Let me rephrase that. The only practical way. Seating a bullet then pulling it only to have to size it again and reseat it would be a pain and some of that equipment is pricey. Not to mention once you seat the bullet again who knows where you are. Looking at seating force is easy to do and throwing out the oddballs can limit potential flyers.

You're right, and pull force truly is meaningless to the subject at hand. Bullets do not push out of necks before powder burn expands necks to release the bullets. The old & hopeless notions otherwise are simply wrong. It's similar to the same thinkers imagining that normal primer striking resizes shoulders, when none of that is happening either.

The only pull force modifier which also directly affects bullet release is crimping. But crimping is not neck tension and you cannot adjust bullet release precisely/finely with it.
There was good testing with crimping posted recently that pretty much showed crimping (when actual crimping into a groove) was so significant a step change to bullet release that it practically negated all other tension adjustments. So this went roundy roundy back to there being no reason to excessively downsize necks -while crimping. Makes sense, and I would never do it, nor FL sizing of necks.
I don't deal with enough recoil, or using magazines, to need crimping. And I use the correct powders to begin with so that I don't need some extremes in tension.

Seating force is currently to best we can do to comparatively correlate NT, given well managed/normalized neck friction.
I measure pre-seating force, with an instrumented mandrel die.
With this I can adjust the force, through sizing length, to match all necks -before seating any bullets.
When this gets to be a battle, I reset the batch with dip annealing. That's pretty rare with my standard minimal sizing plan. Maybe ~30-50 reloads down the road (from initial).

 

[mrdinapoli]

Back after a few days at work....Several thoughts to the above questions and comments.

I have not tried to shoot any similarly prepped and sized rounds on target yet. I have just been experimenting and troubleshooting my set-up. The purpose of my experiment was as much to describe my setup so others can also make use of it, as to get some preliminary data.

With regard to neck tension vs the length of neck sized. There are dies that will allow you to size the length of the neck precisely -- I do believe that Redding makes a bushing die with a micrometer to control the length of neck sized. Other dies like the LE Wilson Arbor die or other press bushing dies would require the "cap" to be screwed in or out to different depths and then to have the length of sizing measured and adjusted. This might work if you leave that die alone and do not adjust it or change bushings, but it would not be very repeatable or precise.

Also, I have two concerns with the idea of controlling neck tension force with adjusting the length of the neck sized. 1) If you are leaving part of the neck unsized to reduce overall tension, you are also running the possibility of increasing the risk of bullet run-out by losing full support for the bullet inside the neck (ie. less than one bullet diameter of support). 2) If the supposition is that NT does not matter at all because the case neck is blown out to chamber neck diameter with powder combustion, then sizing the neck to a greater or lesser length to change NT also would not matter.

Further, I feel that we all agree that the brass of the case neck will expand to chamber neck diameter with powder combustion, and freely release the bullet. However, neck tension or friction or force required for bullet release or any combination will briefly hold the bullet in place until the powder combustion occurs sufficiently for pressure to expand the case neck and freely release the bullet -- even if only for fractions of a microsecond. This is the only way to explain the findings that NT changes have an effect on velocity and accuracy -- otherwise, there would be no effect. Therefore, this suggests that any degree of NT will contribute to delayed bullet release and thus improved combustion efficiency, even if only to a small degree.

The whole idea that NT has at least some effect on accuracy, velocity, and powder burn uniformity is again supported by the findings that crimping affects these parameters. I have to admit that I am still reading about crimping and have yet to try it, but many respected members of this forum have shown that crimping can have significant effects on accuracy, velocity, and SD. Although I don't believe advertising without my own confirmation, Lee Precision does state the following in its description of their Factory Crimp Die (FCD): "Tests demonstrate that even bullets with no cannelure will shoot more accurately if crimped in place with the Lee Factory Crimp Die. A firm crimp improves accuracy because pressure must build to a higher level before the bullet begins to move. This higher start pressure insures a more uniform pressure curve and less velocity variation. Even powder selection is less critical." I have purchased a Lee FCD and will by testing it in the near future.

Mikecr -- One other comment or question, and I am not trying to be argumentative in any way, but just trying to make sure everyone is on the same page... you stated "The only pull force modifier which also directly affects bullet release is crimping. But crimping is not neck tension and you cannot adjust bullet release precisely/finely with it." I do agree that you can not adjust bullet release precisely with crimping, and I agree that crimping is controlled independently of neck tension and friction. However, to me it appears that crimping is essentially the exact same thing as NT, but only applied to a limited area of the neck (at the mouth) and to a greater degree (the neck is reduced past the point of plastic deformation after the bullet is seated). It appears it would exert its force as hoop tension, in a fashion similar to NT as discussed previously, and would be additive to the NT achieved by neck reduction and interference fit discussed above. Further, the discussion regarding NT being irrelevant due to neck expansion and bullet release following powder combustion would also appear to hold true to crimping, as the crimped portion of the neck would also be blown out by pressure causing release of the bullet, and that portion of the neck would not be expected to drag along the bullet jacket (unless, possibly, if the chamber had a very tight neck). I do agree that crimping has the ability to exceed the force of NT on the bullet due to the area and degree of force exerted by the plastically deformed mouth and neck (similar to a narrow tire exerting far more ground contact PSI than a wider tire due to increased surface area), and even more drastically with bullets with cannelures or where crimping may deform the case mouth into the bullet jacket. However, if crimping has been shown to affect powder burn efficiency, velocity, SD and accuracy, then NT must be able to do the same, even only to a small extent.

Two other important suggestions from the findings:

1. I do not feel that seating force is a good surrogate for NT. Although it is true that as NT (defined as neck OD from a loaded round minus OD of a sized case) is increased, seating pressure will increase; there is a point that will be reached where plastic deformation occurs (with use of a mandrel or seating of a bullet) and additional hoop tension or holding force can not generated. At this point, the elasticity of the brass measured as hoop tension against the bullet will reach a maximum point which will not be able to be overcome. Therefore, there will be a point of divergent consistency reached where any increase in seating force will not correspond to an increase in hoop tension exerted on the bullet. This occurred around 0.002" NT with the Hornady bullets in my experiment, but will likely vary by caliber and brass characteristics in other situations.

2. I do agree that overly sizing necks is counterproductive. As previously reported, and as noted above in #1, a point of neck reduction will be reached after which no further neck tension force will be able to be achieved. Past this point, additional sizing will only work on overworking the brass. The exception to this guideline will be if necks are being intentionally oversized to allow more consistent re-expansion with a mandrel.

I believe that the only true way to make any sense of this type of data is to have clean data by reducing the noise. The only device I can see that will provide consistent ram speed and movement, as well as be able to graph force vs distance is the AMP press. The software associated with the AMP press can also allow data sorting by peak pressure, distance at peak pressure, and area under the curve, which will allow for even more detailed analysis and comparisons. I feel that further attempts to produce good data with the analog presses, like those I have on hand, will only provide general trends.

Although not possible now, I would like to acquire an AMP press and test neck bushing reduction vs mandrel expansion vs crimping, seating force vs "release" force, and the correlation of all of these on accuracy, velocity and SD -- what really matters. I would also like to run other experiments, such as what effect does prolonged bullet seating (ie. "cold welding") have on the above, and can bullets be seated long for extended period of time and then bumped deeper to goal depth just before shooting, essentially breaking any cold weld. I will definitely post more info once available.

Best wishes, Mike D.