I've recently began loading pistol on a regular basis and I have a couple questions about COAL on pistol rounds.

I know that in bottleneck rifle rounds, the deeper you seat (to an extent) that the pressure tends to decrease due to an increase in freebore travel.  Also, the closer to the rifling the more accuracy potential is achieved, however the risk of increased pressure should be noted.

On a pistol round, I've come to understand that the opposite is true, that deeper seating has the potential to increase case pressure presumably due to less case volume.

Does loading longer on a pistol round achieve anything accuracy wise?  Most of my reloads recommend a COAL of 1.100" (9mm), while most of the factory rounds measure out at 1.145".  Is this due to the powder they are using filling more of the case?  I don't have a chrono, but my assumption is that if I loaded longer I may run into lower velocities and possibly unburnt powder?  So is there a benefit or is it highly dependent on the powder used?

I know that length plays a roll in reliability, but I'm wondering about accuracy.  Thanks

Tag for answers.


Great question, OP.

I my experience, NO.  In Pistols OAL is set to Feed-Function-Fire, and I have never been able to adjust OAL to affect accuracy in my pistols.  That's pistols, I do not have any revolvers, that mat be a different story.

It seems that reducing bullet jump can improve accuracy at least in auto loaders. The reason I say this is because of how short the lead is on some pistols. Some are so short it makes it nearly impossible to load some cast bullet designs.

With revolvers I can't really see where it would make much difference. The jump from cylinder to forcing cone alone is substantial. Combine this with the fact that nearly all revolver bullets have a canalure and require a crimp, there really is not much room for changing the COAL.

The deep seating causing higher pressure in straight wall pistol ammo is a little over exaggerated in my opinion. It really only comes into play when 1) The COAL for a given load is either purposely or mistakenly load way under or 2) The bullet "set-back" because of some kind of malfunction. From what I have read here on this forum, it seems at least the second of the 2 rarely if ever causes a catastrophic failure AKA KABOOM.

For rifle, loading to contact the lands (or just short of) can be very helpful in obtaining max accuracy but there are variables involved and should be considered before doing so. Usually these loads are "worked up" with the COAL set this way from the start.

For a 115 gr FMJ bullet in 9mm, 1.10" COL is pretty standard, its what I use with good results.  Concurring with the Mod, stay with the loading manual recommended OAL for the specific bullet used.  OAL has a lot to do with function in pistols and revolvers, less with accuracy.  

In 9mm pressure can spike if the bullet goes too deep.  Make sure your brass has good tension and tight grip on the bullets.   If you push a loaded round hard at the nose, the bullet should not depress into the case at all (no change in OAL).