rfwobbly made some excellent points which I agree with fully and have posted the same for years to increase neck tension which resists bullet setback:
- Resize brass fully
- Minimally flare the case mouth to just set the bullet base inside
- Use minimal amount of taper crimp to not reduce bullet diameter
Case wall gets thicker as you move from case mouth towards case base and deeper seated bullets, especially with shorter base 9mm bullets, benefit from increased neck tension which resist bullet setback and produce more efficient powder burn that results in more consistent chamber pressures.
In a recent thread, this was illustrated with 100 gr RNFP bullet with shorter bullet base -
https://www.thehighroad.org/index.php?threads/100-gr-bullet-for-9mm-luger.828393/#post-10680353
As shown below, seating to 1.090" would produce less neck tension than 1.050" or even deeper 1.030".
I pretty much took for granted the bullet size was .355.
Guess I should have been on this forum years ago.
Well, welcome to THR.
As I mentioned in my post #9, not all 9mm bullets are sized .355" and if you are experiencing neck tension issue, you can benefit from using slightly larger sized bullets -
https://www.thehighroad.org/index.p...ping-the-autoloader-9mm.829171/#post-10694224
Speer Gold Dot and TMJ thick plated bullets are highly regarded by many reloaders and guess what? They are sized slightly larger at
.3555". Many match shooters consider Hornady HAP one of more accurate bullets and guess what? 125 gr HAP is sized even larger at
.356".
If you are experiencing neck tension issue and significant bullet setback, I would first make sure my resizing die was adjusted properly to full-length resize the brass/minimally flare the case mouth/avoid too much taper crimp but if these steps won't resolve the neck tension issue, I would consider using slightly larger sized bullets.
Below is close up picture of RMR 124 gr FMJ sized .3555" loaded to 1.130" with .378" taper crimp using once-fired Blazer brass and Lee dies seated/crimped in same step. As you can tell, there is pronounced even bulge around the case neck at bullet base indicating good neck tension. I experience essentially no bullet setback when finished rounds are chambered from the magazine -
https://www.thehighroad.org/index.php?threads/mixed-brass-effects-oal.824238/page-2#post-10605996
And while I am a fan of Lee dies, I do not use the FCD for 9mm loads.