Maximinus Thrax
Expert
Question regarding OAL in pistol calibers and its impact on velocity. First, I'll set the scenario so you can be on the same track that I am.
Goal: Load MO Bullet Co 124gr Lead Round nose projectiles using HS-6 and Titegroup for 9mm. It's the bullet/powder combo I have so here we go...
Problem: Lee Modern Reloading, Hodgdon.com, and Hornady don't have that EXACT combo. However, Lee Modern reloading 3rd edition on pg 510 has data for 125gr projectiles.
Theory: Use the data for 125gr projectiles,apply it to 124gr and keep the OAL longer (as long as it passes "plunk") and stay away from the min/max charges.
Results: loaded and fired at 1.140" and recorded velocities all above 1000 fps which, according to my understanding of power factor for 124gr, is my goal. Cool.
That said, I noticed some issues feeding so, staying above the min OAL I opted to drop it to 1.130 with the same powder charges. I expected pressure to change so I kept an eye on brass and pressure signs. However, velocity averages were lower by an average of 20-30 fps for every load except 1 where velocity increased by about the same range (20-30fps). Pressure signs were most evident on this particular load so won't be going there again.
The part that confuses me is this, given a drop of .010" OAL and approximately the same outdoor temp, why would I see higher pressure but a drop in velocity of an average of 20-30 fps? Lee Modern Reloading did not help me make sense of this so I turn to the collective minds here.
I'll be going back to a couple of the batches that showed no pressure signs and fed reliably for further testing so any further loads will be safe but I'm still perplexed as to why I saw the velocity data that I did.
Goal: Load MO Bullet Co 124gr Lead Round nose projectiles using HS-6 and Titegroup for 9mm. It's the bullet/powder combo I have so here we go...
Problem: Lee Modern Reloading, Hodgdon.com, and Hornady don't have that EXACT combo. However, Lee Modern reloading 3rd edition on pg 510 has data for 125gr projectiles.
Theory: Use the data for 125gr projectiles,apply it to 124gr and keep the OAL longer (as long as it passes "plunk") and stay away from the min/max charges.
Results: loaded and fired at 1.140" and recorded velocities all above 1000 fps which, according to my understanding of power factor for 124gr, is my goal. Cool.
That said, I noticed some issues feeding so, staying above the min OAL I opted to drop it to 1.130 with the same powder charges. I expected pressure to change so I kept an eye on brass and pressure signs. However, velocity averages were lower by an average of 20-30 fps for every load except 1 where velocity increased by about the same range (20-30fps). Pressure signs were most evident on this particular load so won't be going there again.
The part that confuses me is this, given a drop of .010" OAL and approximately the same outdoor temp, why would I see higher pressure but a drop in velocity of an average of 20-30 fps? Lee Modern Reloading did not help me make sense of this so I turn to the collective minds here.
I'll be going back to a couple of the batches that showed no pressure signs and fed reliably for further testing so any further loads will be safe but I'm still perplexed as to why I saw the velocity data that I did.