OAL Question

[ultrablue]

In various discussions overall length comes up as a statistic. I have a Dillon case gauge and thougth this was for diameter and length as a go no go gauge. If you change the overall length of a round from my length of 1.156 to something shorter am I to assume this will produce a higher pressure (less empty space in the case) meaning a higher velocity? I guess I didn't realize this could also be a variable?

[Joe4d]

it may produce a higher pressure and it may produce higher velocity, Its gonna depend on the powder and charge density.

OAL is used for function not to change velocity, use changes in powder and charge weight to change velocity.

If you do shorten your load you still need to re chrono to see whats going on.

[Red Ryder]

We don't use AOL to change velocity because it is dangerous. Small changes in AOL may produce small changes in pressure and velocity but it not proportional and should not be relied upon. As a matter of fact, shortened AOLs may produce exponentially higher pressures without much change in velocity. The end result will blow your gun up and may result in an Emergency Room visit.

[Sarge]

Aside from the dangers of shortening oal while not reducing the charge oal is a critical piece of the puzzle in many guns. My particular G34 is more accurate loaded at 1.13 than it was at my old standby number of 1.15.

A 9mm case gauge is not going to check oal. Your barrel is the best gauge for oal.

[ultrablue]

We don't use AOL to change velocity because it is dangerous. Small changes in AOL may produce small changes in pressure and velocity but it not proportional and should not be relied upon. As a matter of fact, shortened AOLs may produce exponentially higher pressures without much change in velocity. The end result will blow your gun up and may result in an Emergency Room visit.

The OAL for a 9mm is 1.169. Why do I see some OAL's as low as 1.11 and 1.12?

Right now all of my loads are 1.155 to 1.156. My 9mm xdm4.5 cycles fine and knocks down steel. The only unknown for me right now is the power factor and I am planning on a chrono session this Friday with these loads.

[CeeZer]

Some guns have barrels with short throat and thus bullet hits rifling of the barrel sooner. One needs to shorten OAL for such barrels.

It also depends on bullet's profile, more 'pointy' bullets can be loaded with greater OAL.

[Sarge]

Some guns have barrels with short throat and thus bullet hits rifling of the barrel sooner. One needs to shorten OAL for such barrels.

It also depends on bullet's profile, more 'pointy' bullets can be loaded with greater OAL.

+1 The CZ line seems to be pretty short with many oal's around 1.10 in preferred loads.

Bullet shape makes a huge difference. I was loading round nose bullets to 1.15 and picked up some precision moly 147's and had to drop to around 1.10 to get them to chamber without the bullet bottoming out on the rifling.

[Red Ryder]

We don't use AOL to change velocity because it is dangerous. Small changes in AOL may produce small changes in pressure and velocity but it not proportional and should not be relied upon. As a matter of fact, shortened AOLs may produce exponentially higher pressures without much change in velocity. The end result will blow your gun up and may result in an Emergency Room visit.

The OAL for a 9mm is 1.169. Why do I see some OAL's as low as 1.11 and 1.12?

Right now all of my loads are 1.155 to 1.156. My 9mm xdm4.5 cycles fine and knocks down steel. The only unknown for me right now is the power factor and I am planning on a chrono session this Friday with these loads.

You get the minimun OAL from the bullet recipe in the reloading manuals. As a new reloader, I do not go below it. You can adjust it longer to figure out the best OAL for accuracy. Longer OAL will have a small effect on velocity, but not much. I shoot an XDM 9mm. Currently, I am loading N320 4.2 grains with a 124 grain MG bullet. I have tested it at 1.145 to 1.160 and had minimal changes in velocity. Power factors varied from 132 to 128. The recipe calls for the load to be 1.142. N320 fills the case up nicely so I wouldn't go below 1.142. If you do go shorter, the end result could be a compressed load, which is bad.

The powder manufacturer that does the testing publishes it with their load data.

[Red Ryder]

Some guns have barrels with short throat and thus bullet hits rifling of the barrel sooner. One needs to shorten OAL for such barrels.

It also depends on bullet's profile, more 'pointy' bullets can be loaded with greater OAL.

+1 The CZ line seems to be pretty short with many oal's around 1.10 in preferred loads.

Bullet shape makes a huge difference. I was loading round nose bullets to 1.15 and picked up some precision moly 147's and had to drop to around 1.10 to get them to chamber without the bullet bottoming out on the rifling.

Sarge,

Do you load N320 in your Glock 34 at an OAL less than 1.142 (Vihtvouri load manual)? If so, how do you know it would be safe? How do you know you can load shorter and be safe? I am new at this stuff,,,just wanna learn.

[ultrablue]

We don't use AOL to change velocity because it is dangerous. Small changes in AOL may produce small changes in pressure and velocity but it not proportional and should not be relied upon. As a matter of fact, shortened AOLs may produce exponentially higher pressures without much change in velocity. The end result will blow your gun up and may result in an Emergency Room visit.

The OAL for a 9mm is 1.169. Why do I see some OAL's as low as 1.11 and 1.12?

Right now all of my loads are 1.155 to 1.156. My 9mm xdm4.5 cycles fine and knocks down steel. The only unknown for me right now is the power factor and I am planning on a chrono session this Friday with these loads.

You get the minimun OAL from the bullet recipe in the reloading manuals. As a new reloader, I do not go below it. You can adjust it longer to figure out the best OAL for accuracy. Longer OAL will have a small effect on velocity, but not much. I shoot an XDM 9mm. Currently, I am loading N320 4.2 grains with a 124 grain MG bullet. I have tested it at 1.145 to 1.160 and had minimal changes in velocity. Power factors varied from 132 to 128. The recipe calls for the load to be 1.142. N320 fills the case up nicely so I wouldn't go below 1.142. If you do go shorter, the end result could be a compressed load, which is bad.

The powder manufacturer that does the testing publishes it with their load data.

Thanks Red Ryder. Going to the range today for testing. Will let you know the results with the Bullseye powder.

[Sarge]

Sarge,

Do you load N320 in your Glock 34 at an OAL less than 1.142 (Vihtvouri load manual)? If so, how do you know it would be safe? How do you know you can load shorter and be safe? I am new at this stuff,,,just wanna learn.

I load 4.2 N320 at 1.13 with Montana Gold CMJ's. No where near a compressed load by the way.

When I work up a load I take recommendations from here, books etc I start low and work up. But the truth of the matter is with minor loads, unless you really screw something up badly, there is a lot of room for experimentation. When I see short oal loads for CZ's and the like in the same ballpark as what I am working on 1.13 is not going to hurt anything. I check primers during the process for signs of pressure. They look just as rounded off as new ones after firing. No pressure problems means good news to me.

9MAJOR is a totally different story altogether since even starting loads are off the chart! Not a good time to have bullet setback or some other problem.

[rfwobbly]

You are getting your facts jumbled. Please allow me to help.....

The OAL for a 9mm is 1.169.

Not quite. The maximum OAL set by SAAMI is 1.169". Rounds loaded longer may well shoot in your gun, but they will not fit in the magazine. As with all maximum dimensional limits, it often helps to back off even a little more. Different shape bullets are going to jam-up in the mag at different lengths. Also you don't want things so tight that 1 spec of sand reeks havoc. So you may want to do something like never plan load longer than 1.150" just to be safe. That way if your press produces one or two rounds in a batch at 1.154" you're still going to be OK.

Why do I see some OAL's as low as 1.11 and 1.12?

• You may see these in the reloading manuals because that's what OAL that were tested at in the lab.

• You may see people post these on the forums because no two pistol makers cut their barrels the same. Therefore, the same bullet may have to be seated to 2 different OALs to work in 2 different guns. The barrel is always the ultimate judge of maximum OAL.

Here's a cartoon to show some of what's going on....

Right now all of my loads are 1.155 to 1.156. My 9mm xdm4.5 cycles fine and knocks down steel.

That's a half-truth. It would be more correct to say "All my XDM loads are at 1.155 with XXX brand bullet" because I guarantee that if you change brands of bullets your OAL is also going to change.

The only unknown for me right now is the power factor and I am planning on a chrono session this Friday with these loads.

That's all well and good. It's always good to know your FPS and nice to play by the rules. However, I might suggest you shoot the same low power load from sandbags or pistol rest and see if you can tell any difference in accuracy or feeding using OALs of 1.130, 1.140, 1.150, and 1.160". You might just find yourself re-standardizing on something shorter.

Hope this helps!

Edited September 3, 2011 by rfwobbly