Bullet Depth v More Powder in 9mm for more velocity?

TargetTerror · November 21, 2008, 12:14 PM

So I know that adding more powder will obviously yield higher greater velocities (to a point). I also know that in any cartridge, but particularly the small, high pressure pistol cartridges like the 9mm, seating the bullet further into the case will raise pressure. Greater pressure of course can send a bullet down the barrel faster.

So my question is, would you be able to get the same velocity/performance by using less powder with a smaller OAL as you would with more powder with a longer OAL? Or does the smaller OAL simply raise peak pressure without sustaining that pressure long enough to yield more velocity?

Shoney · November 21, 2008, 03:09 PM

Answers to your question Bullet Depth v More Powder in 9mm for more velocity?, are a matter of physics and the following formula determines the changes.

pV=nRT

where

p is the absolute pressure [Pa],
V is the volume [m3] of the vessel containing moles of gas, here it is the volune you allow in the shell case
n is the amount of substance of gas [mol], here it is in solid form as powder
R is the gas constant [8.314 472 m3•Pa•K−1•mol−1],
T is the temperature in kelvin [K].
BORED YET?

Think of it as:
Pressure in the case times Volume of case = 2 Irrelevant numbers RT (for our purposes) times the amount of gas n as being in solid form as powder until the "big bang";
1. the gas constant R remains the same;
2. the temperature T remains constant;
For practical purposes the equation should read PV=n

Now lets do some math. Remember, the two sides of the equation must balance. PV=n

Presume you are shooting your pet load
A. Increased powder = Increased Pressure Increased powder loads produce more gas n, and volume V inside the case remains the same. That means the Pressure must increase to match the increase in gas.
B. Decreased Volume = Increased Pressure Back to the pet load, Now decrease the volume V (by seating the bullet deeper) and keep the gas n the same, in order for the equation to balance, the pressure P must go up.

Bottom line on loading all cartridges at or near max pressure.
1. You must be careful not to exceed max pressures. Powders do not always follow a linear increase in pressure, moreover, they spike drastically at some point. It has been shown that when max loads are exceeded, exceptionally high pressure spikes can occur. It has been suggested by some that high pressure rounds are more susceptible to these pressure spikes.
Quick spikes in pressure tends to rupture cases, thus damaging weapons and body parts. Even if the cases do not rupture, over pressure loads are abusive to equipment and fatigue metal into failure.

2. Bullets can easily set back into cases if care is not taken during loading. Crimp/neck tension is important to prevent set backs, because as the equations show, decreased case volumes increase pressure and it can be to a catastrophic level.

3. What will happen to the velocity???????? Only testing thru a chronograph will give the answers. Because of the variables, it is nearly impossible to predict the exact increase/decrease.
Good Shooting!

WESHOOT2 · November 21, 2008, 07:04 PM

Shortening OAL will virtually always increase pressure, but doesn't increase velocity in any linear fashion.

If you want more speed do something with gunpowder (or the 9x21).

LHB1 · November 21, 2008, 08:13 PM

Shortening OAL WILL increase initial pressure BUT as soon as the bullet starts moving, the volume behind bullet increases dramatically and the pressure will drop. It will NOT give as much velocity as more powder would have done. When the powder burns, the additional volume of more powder will generate greater volume of gas behind bullet to increase bullet velocity more than seating bullet deeper would have.

dahermit · November 21, 2008, 08:32 PM

Loading manuals list over all cartridge length for various bullets. It makes no sense to try to increase velocity by seating bullets deeper into the case, regardless of any velocity increase because over all length is a factor in correct(reliable) cartridge feeding. Save, .03 cents on powder, decrease reliablity...a no brainier.

snolden · November 22, 2008, 06:33 PM

The advice I have always used is to load your bullets as long as possible that they reliably feed for step one.

then dial in a powder load for accuracy and energy as applicable.

THEN and ONLY THEN dial in the COAL for accuracy.

I have never needed to use the third step. Once I get my COAL long and to the length I need for reliability, adjusting the powder has ALWAYS got my accuracy to better than my ability to shoot.

November 21, 2008, 12:14 PM	#1
TargetTerror Senior Member Join Date: October 28, 2006 Posts: 424	Bullet Depth v More Powder in 9mm for more velocity? So I know that adding more powder will obviously yield higher greater velocities (to a point). I also know that in any cartridge, but particularly the small, high pressure pistol cartridges like the 9mm, seating the bullet further into the case will raise pressure. Greater pressure of course can send a bullet down the barrel faster. So my question is, would you be able to get the same velocity/performance by using less powder with a smaller OAL as you would with more powder with a longer OAL? Or does the smaller OAL simply raise peak pressure without sustaining that pressure long enough to yield more velocity? __________________ Head shots are hard, but nut shots are twice as hard.

November 21, 2008, 03:09 PM	#2
Shoney Senior Member Join Date: February 21, 2002 Location: Transplanted from Montana Posts: 2,311	Answers to your question Bullet Depth v More Powder in 9mm for more velocity?, are a matter of physics and the following formula determines the changes. pV=nRT where p is the absolute pressure [Pa], V is the volume [m3] of the vessel containing moles of gas, here it is the volune you allow in the shell case n is the amount of substance of gas [mol], here it is in solid form as powder R is the gas constant [8.314 472 m3•Pa•K−1•mol−1], T is the temperature in kelvin [K]. BORED YET? Think of it as: Pressure in the case times Volume of case = 2 Irrelevant numbers RT (for our purposes) times the amount of gas n as being in solid form as powder until the "big bang"; 1. the gas constant R remains the same; 2. the temperature T remains constant; For practical purposes the equation should read PV=n Now lets do some math. Remember, the two sides of the equation must balance. PV=n Presume you are shooting your pet load A. Increased powder = Increased Pressure Increased powder loads produce more gas n, and volume V inside the case remains the same. That means the Pressure must increase to match the increase in gas. B. Decreased Volume = Increased Pressure Back to the pet load, Now decrease the volume V (by seating the bullet deeper) and keep the gas n the same, in order for the equation to balance, the pressure P must go up. Bottom line on loading all cartridges at or near max pressure. 1. You must be careful not to exceed max pressures. Powders do not always follow a linear increase in pressure, moreover, they spike drastically at some point. It has been shown that when max loads are exceeded, exceptionally high pressure spikes can occur. It has been suggested by some that high pressure rounds are more susceptible to these pressure spikes. Quick spikes in pressure tends to rupture cases, thus damaging weapons and body parts. Even if the cases do not rupture, over pressure loads are abusive to equipment and fatigue metal into failure. 2. Bullets can easily set back into cases if care is not taken during loading. Crimp/neck tension is important to prevent set backs, because as the equations show, decreased case volumes increase pressure and it can be to a catastrophic level. 3. What will happen to the velocity???????? Only testing thru a chronograph will give the answers. Because of the variables, it is nearly impossible to predict the exact increase/decrease. Good Shooting! __________________ I pledge allegiance to the Flag - - -, and to the Republic for which it stands….Our Forefathers were brilliant for giving us a Republic, not a democracy! Do you know the difference??? and WHY?http://www.wallbuilders.com/LIBissue...les.asp?id=111 Last edited by Shoney; November 21, 2008 at 03:20 PM.

November 21, 2008, 07:04 PM	#3
WESHOOT2 Senior Member Join Date: February 20, 1999 Location: home on the range; Vermont (Caspian country) Posts: 14,324	all blowed up Shortening OAL will virtually always increase pressure, but doesn't increase velocity in any linear fashion. If you want more speed do something with gunpowder (or the 9x21). __________________ . "all my ammo is mostly retired factory ammo"

November 21, 2008, 08:13 PM	#4
LHB1 Senior Member Join Date: March 25, 2005 Location: Houston, TX Posts: 1,545	Shortening OAL WILL increase initial pressure BUT as soon as the bullet starts moving, the volume behind bullet increases dramatically and the pressure will drop. It will NOT give as much velocity as more powder would have done. When the powder burns, the additional volume of more powder will generate greater volume of gas behind bullet to increase bullet velocity more than seating bullet deeper would have. __________________ Good shooting and be safe. LB

November 21, 2008, 08:32 PM	#5
dahermit Senior Member Join Date: October 28, 2006 Location: South Central Michigan...near Posts: 6,501	Bullet seating depth. Loading manuals list over all cartridge length for various bullets. It makes no sense to try to increase velocity by seating bullets deeper into the case, regardless of any velocity increase because over all length is a factor in correct(reliable) cartridge feeding. Save, .03 cents on powder, decrease reliablity...a no brainier.

November 22, 2008, 06:33 PM	#6
snolden Senior Member Join Date: January 25, 2006 Location: N. E. AZ Posts: 387	The advice I have always used is to load your bullets as long as possible that they reliably feed for step one. then dial in a powder load for accuracy and energy as applicable. THEN and ONLY THEN dial in the COAL for accuracy. I have never needed to use the third step. Once I get my COAL long and to the length I need for reliability, adjusting the powder has ALWAYS got my accuracy to better than my ability to shoot.