School me on bullet and powder grain relationship please

[calebp]

Hey guys,

Just started reloading about a week ago. Absolutely hooked. Rolled up 250 147 gr 9mm with 3.3 grains of vv n320. Pure sex suppressed. Had 100 115 I was going to load up as I'm out of 147s at the moment and just want to do some reloading. Check vv's website for data and it shows 3.9 as staring load. Why do you use more powder for a lighter bullet? Seems counterintuitive.

Thanks!
Caleb

 

[woodstock]

That's because a woman wrote it, and no man understands a woman.

 

[mkdhotrod]

Has something to do with powder burn rate and amount of oxygen available in the casing. I'll let one of the experts chime in.

 

[snatch3838]

Several reasons
Bullet is larger so there is less room in the case has to go father in not father out. (Take special note tho that cause when your star. Quest for accuracy the powder needs to be close to 100% of volume some like compression some powders hate it)The heavier bullet is slower so burn time and speed of burn is calculated in there but not exAct on how. Heavier bullets will also do better with slower powders. Longer barrels do better with slower powders also cause of more time to burn. The main reason though is pressure is what drives the bullet. The heavier bullet will drive up pressure faster so it needs less powder to do the work as well as to not over pressurize the chamber

 

[Springfield 1911]

Several reasons
Bullet is larger so there is less room in the case has to go father in not father out. (Take special note tho that cause when your star. Quest for accuracy the powder needs to be close to 100% of volume some like compression some powders hate it)The heavier bullet is slower so burn time and speed of burn is calculated in there but not exAct on how. Heavier bullets will also do better with slower powders. Longer barrels do better with slower powders also cause of more time to burn. The main reason though is pressure is what drives the bullet. The heavier bullet will drive up pressure faster so it needs less powder to do the work as well as to not over pressurize the chamber

Here is the answer! Pressure is key. This is the reason some powders do not have to fill the case to perform.

 

[Flashover16]

Here is the answer! Pressure is key. This is the reason some powders do not have to fill the case to perform.

THERE YOU GO!
its really all about case capacity, the amount of space determines the pressure of a particular powder when its ignited.
the smaller the case capacity then the higher the pressure and pressure peak can be. look at the 380/ 9 MM/ 38 super as a example, using the same exact projectile you will see that the case capacity is smaller in the 380 VS 9 MM and the 9 MM vs the 38 Super and so loading is lighter to produce a safe pressure..
the heavier the projectile then the deeper it protrudes into the case, thereby reducing case capacity.
same thing by using a different material for the same weight projectile. a all copper projectile will be longer than a jacketed, lead projectile as copper is a lighter material and so the projectile must be longer if the same weight, frangible is the same.
so loading density for such projectiles is normally less and OAL may be longer.
hope this helps.

 

[jjrock]

Real good info in this thread!

 

[Twitch2120]

Heavier bullets in a given caliber tend to be longer which reduces cases capacity but also means there is more bearing surface in the bore. More contact means more friction which means it's harder to push which spikes pressure. Crimps also can increase pressure by holding the bullet in the case longer.

 

[YOTESHOOTER]

Try to keep the case fill with a 85% up to 98% fill if possible..

just a suggestion..

The above info will be very valuable to you over the coming years of your new found passion.

 

[givejunkfree]

There are formulas. Build capacity vs. projectile weight, density, and air space. My dad was a NAA rocket scientist and he explained propulsion v.s decimation (explosive capacity) relative to trajectory, but, I never understood a greek symbol he wrote.