Powder PSI

[sdmc530]

Originally Posted by milkmanjoe

Am thinking about the .308. When seated, the compression of the powder. The bullet will not fire efficiently without compressing the powder, but is there a general PSI that the powder is compressed to to max it out while being safe?

I get ya... I will ask my FIL about this. He is a rifle guy and been loading longer than I have. You are the first person to ever ask this on a forum that I am aware of. You must be one of those thinkers or something

[milkmanjoe]

Originally Posted by sdmc530

I get ya... I will ask my FIL about this. He is a rifle guy and been loading longer than I have. You are the first person to ever ask this on a forum that I am aware of. You must be one of those thinkers or something:D

hehehehe...always need to know the specifics.

[Gatorade]

Most loads aren't compressed. Usually they will have an abbreviation CL or something to indicate it is compressed as compression can increase the PSI quickly and dangerously. Some types of powder may take up more space in the case but very few actually squeeze the bullet down far enough to compress the powder. When creating a compressed load you fill the powder according to the weight of the charge which will fill above where the bottom of the bullet would seat. Then the projectile being seated will compress the load when seated to the OAL.

[milkmanjoe]

Originally Posted by Gatorade

Most loads aren't compressed. Usually they will have an abbreviation CL or something to indicate it is compressed as compression can increase the PSI quickly and dangerously. Some types of powder may take up more space in the case but very few actually squeeze the bullet down far enough to compress the powder. When creating a compressed load you fill the powder according to the weight of the charge which will fill above where the bottom of the bullet would seat. Then the projectile being seated will compress the load when seated to the OAL.

So there can be airspace between the powder and the bullet?

[Gatorade]

Originally Posted by milkmanjoe

So there can be airspace between the powder and the bullet?

Depending on the load yes. Sometes a lot,msometime a a little. I have some Trailboss that is a much fluffier powder to take up more space because 231 loaded in a 38-40 case woul only fill to about a third of the case. Then the powder sits on the bottom of the case and may not ignite correctly. Not enough to Squibb but maybe a lower velocity.

I loaded some .32 Magnum and could double charge the load without over flowing the case. That means single charge would take less than half of the case.

Yes many times there is a bit of space between the top of the powder and the bottom of the bullet. So a compressed load would be over filled with powder and squeezed or compressed down. VERY DANGEROUS with a powder that the burn rate is not appropriate for a compressed load.

For example, we load powder by weight. But 1 grain of W231 and 1 grain of AR Comp and 1grain of Trail Boss would all take up different volumes. Then compound the faster burn of the AR comp and you could have a high pressure spike than if you loaded the same volume of Trail Boss.

[brownie]

Originally Posted by milkmanjoe

So there can be airspace between the powder and the bullet?

If there isn't you're likely to get a BIG surprise.

[milkmanjoe]

Originally Posted by brownie

If there isn't you're likely to get a BIG surprise.

And this is a reason I asked about powder compression. Reading the boards some guys complain about using powders that require them to damn near jam the bullet in to get the desired OAL. So, as I'm reading this, I'm thinking about the PSI of packed powder. I'm sure this all has to do with burn rates in some way to max out the load.

[brownie]

Originally Posted by milkmanjoe

And this is a reason I asked about powder compression. Reading the boards some guys complain about using powders that require them to damn near jam the bullet in to get the desired OAL. So, as I'm reading this, I'm thinking about the PSI of packed powder. I'm sure this all has to do with burn rates in some way to max out the load.

I keep chambers loaded with the guns in rotation. Not having to unload sd round/s to shoot to practice, having dedicated practice guns. No need to worry about set back from constant chambering. I worry more about mucking the rim up so the extractor doesn't get a solid a purchase as it should on a new round. Making sure to load the round back in the mag [ to rechamber it ] with a clean spot on the rim, not on a gouged/deformed areas previously grabbed by the extractor

[Gatorade]

Originally Posted by milkmanjoe

And this is a reason I asked about powder compression. Reading the boards some guys complain about using powders that require them to damn near jam the bullet in to get the desired OAL. So, as I'm reading this, I'm thinking about the PSI of packed powder. I'm sure this all has to do with burn rates in some way to max out the load.

Remember you are talking about 3 different variables here.

1 Powder
2 Bullet
3 OAL

Not all 150 ge bullets are the same length. Not all powders have data for all calibers and OAL is dependent upon the bullet length and the powder charge. That is why different powders have different OAL for one bullet and may have a different OAL for the same bullet with a different powder charge.

[Riverpigusmc]

Originally Posted by Gatorade

Most loads aren't compressed. Usually they will have an abbreviation CL or something to indicate it is compressed as compression can increase the PSI quickly and dangerously. Some types of powder may take up more space in the case but very few actually squeeze the bullet down far enough to compress the powder. When creating a compressed load you fill the powder according to the weight of the charge which will fill above where the bottom of the bullet would seat. Then the projectile being seated will compress the load when seated to the OAL.

^this. Pressure in a firearm is measured in CUP (copper units of pressure). Some powders are meant to be compressed, most are not. Some powders are position sensitive (i.e. if they lay along the bottom of the case, ignition will suffer). Some powders characteristics are such that free space causes pressure spikes. In that case, OAL is reduced, or fillers are used. That is why loading manuals always list minimum and maximum overall length for each bullet and powder combination