Myth Busting Neck Tension and Bullet Setback

DISCLAIMER: Testing conducted for this thread was done by a random poster on the internet forum with possible unreliable equipment. Test data deemed unscientific and use them at your own risk.

Neck tension and bullet setback issues and questions have been posted on recent threads and I decided to do some more myth busting.

Newest issue posted is with X-Treme 100 gr RNFP plated bullets used for 9mm - https://www.thehighroad.org/index.p...e-49-1000-free-shipping.828972/#post-10710394

Since 100 gr RNFP bullets have shorter bullet base, I suggested using shorter OAL/COL on this thread to increase neck tension and prevent bullet setback for more consistent chamber pressures (It's not finished OAL but "chambered" OAL that will affect group size ) - https://www.thehighroad.org/index.php?threads/100-gr-bullet-for-9mm-luger.828393/#post-10680353



So I loaded up X-Treme 100 gr RNFP bullets in various headstamp cases and measured bullet setback:

- Frankford Arsenal dial calipers verified with .355"+ pin gauge - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10523549
- Lee dies were used
- Finished OAL used was around 1.040"
- Since bullets were sized .355", taper crimp used was .377" - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10567453
- Dummy rounds (no powder, no primer) were measured before/after they were fed/chambered in Glock 22/23 using KKM/Lone Wolf 40-9 conversion barrels and 9mm magazines without riding the slide

Measurement #1 with X-Treme 100 gr plated RNFP (More to follow):

These headstamp cases did not experience bullet setback:

• CBC
• GECO
• PMC
• R-P
• S+B
• Starline
• WIN

These headstamp cases experienced bullet setback (After Glock 22/KKM barrel, After Glock 23/Lone Wolf barrel):

• AGUILA: -.0005", -.0005"
• BLAZER: -.002", -.002"
• BLAZER: -.001", -.002"
• BLAZER: -.002", -.003"
• FC: -.001", -.001"
• .FC.: -.002", -.002"
• .FC.: -.001", -.001"
• .FC.: -.001", -.001"
• GFL: -.001", -.001"
• Perfecta: -.001", -.001"
  
• PPU: -.0005", -.001"
• Tulammo: -.0005", -.001"

I plan to conduct more measurements and test other brands/sized bullets (.355", .3555", .356") to shed more light on the subject.

SUMMARY: So based on my initial measurements, if you are shooting for groups, I would suggest you use headstamp cases that do not result in bullet setback (in your pistols) for greater "chambered" OAL consistency.

UPDATE from post #38: Before I started this thread, I was actually preparing a myth busting thread for case wall thickness. What I didn't realize was there were variables I did not factor that could overshadow other variables to produce neck tension and subsequent bullet setback if neck tension was insufficient:

• While most of us focus on case wall thickness near case mouth (.010"-.012" average thickness), this is NOT where most of friction with bullet occurs to establish neck tension.

• To me, most of neck tension occurs below case mouth likely near mid point of bullet to bullet base where case wall thickens much more than at case mouth.

• This is why taper crimp plays a very small part in increasing neck tension as taper crimp is usually applied near case mouth.

• When neck tension/significant bullet setback issue is posted, we often suggest to ensure the brass is full-length resized and/or to use smaller expander/flare which reduces the ID/OD of case neck below the case mouth.

As to measuring case wall thickness at case mouth:

• And this was the biggest realization - Depending on headstamp, case wall thickness varied at different points around the case mouth and multiple measurements were needed.

• Yes, case wall thickness is not often consistent. Some headstamp vary with less than .001" but some others vary with over .002" and this explains why some loaded rounds have out-of-round case neck.

• I initially took 4 measurements around each case mouth at 12/3/6/9 O'clock and found case wall thickness on the same case could vary up to .001"-.002" which significantly affected case wall thickness measurements since typical case wall thickness measured .010"-.012" on average (.002" range).

For these reasons, I decided to not pursue the "Myth Busting Case Wall Thickness" thread and instead started this "Myth Busting Neck Tension and Bullet Setback" thread as I figured measurable bullet setback was ultimately more significant to chamber pressure build, muzzle velocities/SD and group size. And of course, range testing will be conducted to verify our finding on bullet setback.

More on post #49 - https://www.thehighroad.org/index.p...nd-bullet-setback.830072/page-2#post-10711561

JimKirk said:

BDS ... Did the group that "held" have slightly thicker brass than the group that didn't?

Click to expand...

I was actually preparing the "Myth Busting Case Wall Thickness" thread when I started this one.

higgite said:

What myth did you bust?

Click to expand...

I am gearing up for the "Mother Of All Bullets" thread and wanted to standardize/finalize a few things before I start that thread. I want to approach that thread with the most consistent test loads as possible.

Group size ultimately factors in variables such as chamber pressure consistency, powder charge variance, bullet consistency, muzzle velocity variance, etc. Bullet setback when fed/chambered from the magazine factors in variables such as case wall thickness, brass condition, brass work hardening, neck tension, etc.

The myth I wanted to confirm or bust was the notion of certain headstamp "claim" to be thinner or thicker case wall translating to neck tension and bullet setback but realized other factors such as brass condition may overshadow and ultimately sum of these factors would manifest in measurable bullet setback. So I decided to measure bullet setback instead (which is much easier than measuring case wall thickness several times around the case mouth as case wall thickens towards the case base ).

Based on measurements collected, I will next do a comparison range test between BLAZER/.FC. and WIN brass loads to see if there is a noticeable difference in group size.

I did more measuring and this is what I have so far:

- Frankford Arsenal dial calipers verified with .355"+ pin gauge - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10523549
- Lee dies were used
- Finished OAL used was around 1.040"
- Since bullets were sized .355", taper crimp used was .377" - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10567453
- Dummy rounds (no powder, no primer) were measured before/after they were fed/chambered in Glock 22/23 using KKM/Lone Wolf 40-9 conversion barrels and 9mm magazines without riding the slide

Measurement #2 with X-Treme 100 gr plated RNFP at 1.040" OAL:

These headstamp cases did not experience bullet setback:

• CBC
• GECO
• S+B
• Starline
• WIN

These headstamp cases experienced bullet setback (After Glock 22/KKM barrel, After Glock 23/Lone Wolf barrel):

• AGUILA: -.0005", -.0005"
• AGUILA: -.001", -.001"
• AGUILA: -.0005", -.0005"

• BLAZER: -.002", -.002"
• BLAZER: -.001", -.002"
• BLAZER: -.002", -.003"

• FC: -.001", -.001"
• FC: -.002", -.002"
• FC: -.0005", -.0005"

• .FC.: -.002", -.002"
• .FC.: -.001", -.001"
• .FC.: -.001", -.001"

• GFL: -.001", -.001"
• GFL: 0.0", 0.0"
• GFL: 0.0", 0.0"

• PERFECTA: -.001", -.001"
  
• PERFECTA: -.0005", -.001"
• PERFECTA: -.0005", -.0005"

• PMC: -.001", -.001"
• PMC: 0.0", 0.0"
• PMC: 0.0", 0.0"

• PPU: -.0005", -.001"
• PPU: -.0005", -.0005"
• PPU: 0.0", 0.0"

• R-P: -.001", -.001"
• R-P: -.001", -.001"
• R-P: 0.0", 0.0"

• SPEER: -.001", -.002"
• SPEER: -.002", -.002"
• SPEER: -.001", -.002"

• Tulammo: -.0005", -.001"
• Tulammo: -.0005", -.0005"
• Tulammo: 0.0", 0.0"