Changing velocity

[wingnut]

Will longer AOL lower velocity.

[robertbank]

It should reduce pressure, by how much...who knows.  In playing with OAL of loads I have not noticed any meaningful reduction in velocity or more importantly practical accuracy in the handguns I use,  

Not a very scientific answer but the best I can offer.

Take Care

Bob

 

[Yeti]

Pressure, yes.  Velocity, likely.

There is a fair difference in my 40 long loads and standard 40 loads.  Can not use the exact same recipes.  I need to bump up the charge wt. by a couple of tenths when working up final loads to be close in PF.

What kind of difference in OAL are we talking about?   

[Yeti]

For 9mm specifically?  At 1.15 compared to another at 1.12 should be modestly slower, but it all depends on the variables/components used.  

[Hi-Power Jack]

40 minutes ago, wingnut said:

Will longer AOL lower velocity.

Sometimes.  Velocity will never increase with longer AOL, but it can decrease.  

[36873687]

I do know in my 40 standard loads 1.145 an my 2011 at 1.180 can't recall what but yes fps go down longer u go

[9x45]

As OAL increases, maintaining the same bullet weight, velocity decreases because velocity is a function of pressure (which you cannot measure without a test barrel). It may, or may not be significant, for an .03" change in your gun and the powder you are loading, especially if you are chrono'ing mixed brass, that has to be same heads tamp for consistency. Certainly going from 1.100" to 1.165" will result in a measurable decrease.

Edited September 8, 2016 by 9x45

[IDescribe]

The answer is yes, definitely, but you're going to be talking about differences in the range of maybe 5-10 feet/sec per .01 difference in OAL, depending on powder, bullet weight, etc..  

Keep in mind that if you increase OAL far enough that the bullet is engaged with the rifling when the pistol is in battery, the trend will reverse itself and both pressures and velocities will experience a spike.

Also keep in mind that this result is not about the actually overall length, but instead about how deeply the bullet is seated into the case.  It's an important difference to note.  A lot of people will look at an OAL in load data and look at the OAL with the  bullet they're using, which is a different bullet, and make direct comparisons there, but since these are different bullets, the OAL itself will not reflect how deeply the bullets are seated into the case, and it's not an apples to apples comparison.