How OAL affects other variables

[Dougfir]

I've been reading a bunch about OAL and would like to bounce what I think I've learned, off all you very experienced handloaders. My understanding is:

For the same powder charge, increasing OAL will reduce pressure and velocity (unless you touch the lands, in which case you could cause a pressure spike).

For the same powder charge, decreasing OAL will increase pressure and velocity.

However, increasing OAL creates more capacity, so by using a longer OAL, when working up a load, you can use more powder and get more velocity from the same pressure level. So, in effect, using a longer OAL than is published in a manual means that your potential velocity is greater and the pubished max load should go up slightly (I'm guessing that quantifying this is one of the things that Quick Loads is nice for).

Does this sound right to everyone?

 

[djauofd]

I've been reading a bunch about OAL and would like to bounce what I think I've learned, off all you very experienced handloaders. My understanding is:

For the same powder charge, increasing OAL will reduce pressure and velocity (unless you touch the lands, in which case you could cause a pressure spike).

For the same powder charge, decreasing OAL will increase pressure and velocity.

However, increasing OAL creates more capacity, so by using a longer OAL, when working up a load, you can use more powder and get more velocity from the same pressure level. So, in effect, using a longer OAL than is published in a manual means that your potential velocity is greater and the pubished max load should go up slightly (I'm guessing that quantifying this is one of the things that Quick Loads is nice for).

Does this sound right to everyone?

I am not a reloading expert but from experience the body of what you are saying is true. With reloading for my 270 win with a 1 x 8 twist barrel loading the Berger 170 gr to start 20 thousands of lands stretched the load from a Sammi COl of 3.34 to 3.495 I have founds that pressure and velocities were down from published loads at Sammi COL for specific powders. This make perfect sense from a scientific perspective. As you are increasing the cartridge volume as you move the bullet further out. You than can in turn place in more powder to bring pressure up to the max for that cartridge. Be mindful though that I have found the free space or throat to be differrent in barrels manufactured by differrent manufacturers. Significantly so. Therefore when using loads that max velocity always drop back a couple of grains and run a quick ladder up to confirm that loads will fire in both rifle. Example the free throat of the McGowen Precision 270 win kissed the lands at 3.530 while a standard Remington 270 win kissed the lands a 3.622. So if you worked a load for the Remington barrel and put it 10 thousandth off the lands you would be in lands on the McGowen barrel which if you were at a max sammi load the McGowen barrel firing of an identical round would show an extreme pressure spike which could possibly have catastrophic results.

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[woods]

The "case" volume has much less effect on the pressure than you are thinking. Brass is malleable (we move it around with hand tools and presses) and does little to retard the pressure building within it as the powder is ignited. Pressure does not peak until the brass is ironed to the chamber walls, the case head is slammed back to the bolt face and the bullet is against the lands. The bullet is most often .008" larger than the diameter of the lands and it takes significant force to "engrave" the bullet into the lands and push it down the barrel.

When the brass is ironed to the walls, case head against the bolt face and bullet hitting the lands, then you have the internal volume that will determine your "combustion chamber". The bullet against the lands or close to the lands will take more pressure to start it's trip down the barrel. Analogy being putting your front wheels against a curb or getting back a few feet and getting a running start - how much comparative power/rpms does it take in each situation. IOW seating further from the lands reduces the pressure needed to start engraving the bullet

When doing seating depth tests, I have usually seen a decrease in velocity as I seat further from the lands. Sometimes there is a minimal effect but I have never seen an increase in velocity when seating deeper.

IOW don't think of pressure by calculating the internal volume of the brass, it is the volume of the combustion chamber that matters

 

[30-338]

I've been reading a bunch about OAL and would like to bounce what I think I've learned, off all you very experienced handloaders. My understanding is:

For the same powder charge, increasing OAL will reduce pressure and velocity (unless you touch the lands, in which case you could cause a pressure spike).

For the same powder charge, decreasing OAL will increase pressure and velocity.

However, increasing OAL creates more capacity, so by using a longer OAL, when working up a load, you can use more powder and get more velocity from the same pressure level. So, in effect, using a longer OAL than is published in a manual means that your potential velocity is greater and the pubished max load should go up slightly (I'm guessing that quantifying this is one of the things that Quick Loads is nice for).

Does this sound right to everyone?

I guess you posting about this maybe

http://www.bergerbullets.com/wp-content ... 3/COAL.pdf

I agree QL would help.

 

[Nimrod84]

I agree with Woods when it comes to normal rifle catridges, with one caveat or other consideration.

Handgun cartridges or some "small" rifle loads with very quick burning powder, act very different and you can see pressure spikes with a reduction of case volume.

Accurate powder notes on their FAQ - http://www.accuratepowder.com/faq/ - that a 1mm difference in a handgun cartridge OVAL can raise the peak pressure by up to 20%, while that same amount in a rifle cartridge will have a small or insignificant effect.

Fredj338 third post down at: https://www.glocktalk.com/threads/oal-r ... n.1542266/ reiterates this.

Edited to add - Practically speaking, when working up a rifle cartridge I start close to the lands (.015"-.02" off) and then I am comfortable that my pressure will drop as I seat the bullets deeper into the case. If I am 0.1"+ off the lands I do proceed slowly and carefully watch to make sure that I'm not getting any increased pressure signs, but I haven't seen anything yet. I normally use slow powders for a given load.

I don't reload handgun cartridges, so this is hearsay, but my friends start short at the recipe OVAL and then they feel comfortable moving the bullet out as long as they aren't into the lands. They also tend towards mid pressure loads for safeties sake.

 

[ShadeTree]

I'm no expert either but I try not to tempt the sleeping bear and pay attention to OAL listed in published load data when working up a load with a particular powder and bullet. If I'm loaded shorter than listed data, I proceed past the middle range loading with perhaps more careful scrutiny.

Some published data even states "minimum OAL" lengths in their data when listing a powder and bullet for that cartridge. In other words if you're going to approach and use their published max powder charge for that powder and that bullet, make sure your OAL is at least as long as published.

I've noticed sometimes significant max powder charge weight differences of the same powder and bullet, between 2 different load data sources. The difference between the 2 is almost always a longer tested OAL in the source with the higher charge weight.

There's more to it than just that, but in general it pays to pay attention to ALL the details, not just max charge weights and speeds listed for a particular bullet and cartridge.

 

[ozarkpugs]

I agree with Woods when it comes to normal rifle catridges, with one caveat or other consideration.

Handgun cartridges or some "small" rifle loads with very quick burning powder, act very different and you can see pressure spikes with a reduction of case volume.

Accurate powder notes on their FAQ - http://www.accuratepowder.com/faq/ - that a 1mm difference in a handgun cartridge OVAL can raise the peak pressure by up to 20%, while that same amount in a rifle cartridge will have a small or insignificant effect.

Fredj338 third post down at: https://www.glocktalk.com/threads/oal-r ... n.1542266/ reiterates this.

Edited to add - Practically speaking, when working up a rifle cartridge I start close to the lands (.015"-.02" off) and then I am comfortable that my pressure will drop as I seat the bullets deeper into the case. If I am 0.1"+ off the lands I do proceed slowly and carefully watch to make sure that I'm not getting any increased pressure signs, but I haven't seen anything yet. I normally use slow powders for a given load.

I don't reload handgun cartridges, so this is hearsay, but my friends start short at the recipe OVAL and then they feel comfortable moving the bullet out as long as they aren't into the lands. They also tend towards mid pressure loads for safeties sake.

Agreed 100%and I have found that 30/30 rounds seated too far in ( because of light crimp and tube spring pressure) can get scary hot also .

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