OAL vs PSI

[Nevada Ed]

During my test I have come across loads with a minimum oal and loads with a maximum length that are very close in fps.
For example:

115gr plated with a fast powder..
oal 1.12" 4.2grs ... 1073 fps
oal 1.14" 4.8grs ... 1092 fps

124gr plated with med. fast powder..
oal 1.14" 4.5grs ... 1097 fps
oal 1.16" 4.8grs ... 1085 fps

Would there be a reason to pick one OAL over the other due to the amount of powder used or maybe the OAL length of the loads?
Just wondering if a "Short" +P would be better than a "Long" OAL +P ?

The 9mm has a lot more options than my 38 specials, ever had !!
I can see where I can go through a lot of powder just trying to figure out what the best load might be.

However it is nice to have a weapon that is so accurate with eight powders that makes it so hard to choose which way to go.


PS;
Without a cannelure & crimp, taking a load apart is a piece of cake. Got to love that !!

 

[scooter123]

I'm just spit balling here but with a fast powder I think that loading a fast powder on the long side is a somewhat safer approach. In theory the added case volume at initial ignition should slow the rate of rise in pressure and probably slow the powder burn slightly. Those are both good things in a high pressure handgun load with a small case like the 9mm Parabellum.

However, the factor countering that approach is Ignition Efficiency. Some powders just don't ignite well unless a specific pressure level is achieved. This is usually an effect seen with slower powders but there are probably fast powders out there that are pressure dependent to some extent for good ignition. If you see your velocities varying more than desired reducing the OAL may provide a solution. Just keep in mind that those lengths listed in the published load tables are MINIMUM lengths when loading at or near the maximum recommended charge.

Finally I have to question your choice of using a fast powder in a Plus P load. Because your produced velocity wont match what can be achieved using a slower powder at a normal for caliber pressure. For example if you take a look at the load data for Vihtavouri 3N37 you'll understand why some of us are willing to pay the somewhat high asking prices for this excellent powder. Because in a 9mm or 38 special you don't need to resort to pressure extremes to achieve a load that packs in a lot of velocity.

 

[Jamie]

The only reason I can think of to choose OAL based on velocity might be for hollow points. There definitely seems to be a bottom line velocity wise that will produce adequate expansion, of course, adequate expansion doesn't mean adequate penetration. For 'ball' ammo, other than minimum velocity to meet competition requirements, accuracy is the main thing. Rifle ammo seems to be affected by OAL, not so much pistol, at least that is what I've read, haven't really tested that in my pistol reloading.

 

[David R]

I let my gun and magazine decide OAL if I can. What fits in the chamber with the longest OAL is the first step, then it has to fit in the magazine and cycle flawlessly. IF I can , the cartridge headspaces on the bullet, not the case for a better fit. This is real important in my 45 autos.

I don't think OAL in a few thousandths has much to do with pressure. For me its bullet fit, accuracy and function.

I have been a bullet caster for 25 years both pistol and rifle.
David

 

[Nevada Ed]

I have had loads in my 22-250, 270 and 30-06 with light target loads with the bullet at or touching the rifling for its best accuracy. The only problem with this, is that the load has to be fired ! There is no removing a load, due to the possibility of the bullet being pulled and powder dumped in the rifles action during removing.

Most of the articles I have read on pistol loading has stated that a .003" distance off the lands is needed.............
I have no idea of what the pressures would be with a maximum length load, with "No Jump" to the barrel and if it should be done. Maybe with light target ammo, but then there is the problem of a "Stuck" bullet if you do not fire the load and try to eject it. I am sure that the slide slamming home will place the round on the lands or rifling........one would think, any way?

The Nato Ball ammo is at 1.165" which has a little lee way from the maximum OAL of 1.169". I don't know if it is a safety thing or set for better feeding or accuracy.

I think I will hold off on the "Flush" fit for now and hope the loads with a little "Air" between the parts, works out, for now............

Good shooting.

 

[H Richard]

OAL differences can enhance or detract from accuracy. Within pressure limitations, use the one that gives you the best accuracy. The way I work up my loads is to build the powder load first, then fine tune with the OAL.

 

[OKFC05]

In my experience in loading many thousands of 9MM that gets used in over a dozen different guns each year, loading so the cartridge fits in a SAAMI cartridge gauge without interference is the "path of least regret."
Why?
1. It will fit in any SAAMI chamber. You DON'T want a long 9mm that sticks in the rifling.
2. It is most likely to feed in any common semi auto.
3. It makes far less difference in 9mm for practical accuracy to make small length adjustments than you would think.
4. The bullet is the dominant factor in 9mm accuracy, and the loader needs to concentrate on reliability, with enough power to function the gun.

Lots of little things you might tinker with in a .30 cal bench rifle just do not matter in a 9mm pistol.