Bullet depth vs. powder charge vs. velocity

SEHunter · January 1, 2011, 11:00 AM

Please bear with me...If you have a random loaded cartridge, does seating the bullet deeper require less charge or allow for a slightly higher charge? I realize the deeper the bullet sits, the less capacity there is but it has also been said that the bullet being at or on the lands increases pressure.

Would i have a higher velocity with the same exact charge while the bullet is close to the rifling or set back as deep as say a factory round? I have a couple of accurate shooting loads for my 22-250 but the velocities are slower than factory rounds. I would like to exceed or atleast match those velocities and i havent experimented with bullet seating depth so i just wanted to have this info before i use the same powder charge. Thanks guys.

brickeyee · January 1, 2011, 11:08 AM

Peak pressure blows up guns, and is directly affected by case volume and distance to the lands.

Average pressure drives bullets faster.

The problem is keeping peak pressure within safe limits while getting a higher average pressure to increase velocity.

SEHunter · January 1, 2011, 11:32 AM

yesterday, i had a load that was raised a half grain and the velocity was slower than the exact load with a half grain less. I know from load data that i was in the max range. Can it be said that the extra half grain pushed the load out of the average pressure range? Is a drop in velocity with higher charges always a sign of peak pressure?

Shoney · January 1, 2011, 01:58 PM

SEHunter

A decrease in the case volume, seating the bullet deeper, results in higher pressure. A large capacity case will have less pressure increase, when compared to a small capacity case, if the depth change is identical; i.e. 308 vs 300WM.

A bullet set at zero inches off the lands (touching the lands) will have more pressure than a bullet seated at 0.005" off. The farther off the lands up to a point (unknown in each weapon without pressure sensors) the presure will decrease, then start to increase again because of reduction of volume in the case.

If you want more velocity with no decrease in accuracy, you will just have to experiment with seating depths of 0.050 to 0.020 off the lands, and an increase in powder charge. Many weapons have the lands so far back, you will not be able to keep one diameter of the bullet in the case neck. You may need to change powders and start the process all over again.

The powders used in factory cartridges is usually specifically blended for the factory and is not available to the reloader.

SEHunter · January 1, 2011, 05:21 PM

Thanks. I think im going to start over and test one powder at a time. I usually have 2 different loads of about 3 or 4 different powders each time i shoot. Thats too overwhelming to deal with seating depth while trying to pick a powder at the same time. I think i need to get the best combo with each powder then go back and compare the powders. Probably is the better way anyway. Thanks again.

Lost Sheep · January 1, 2011, 05:58 PM

SEHunter,

Yes, the one change raises pressure and the other change lowers pressure, as Shoney correctly explains.

Now, here's the hard part.

Quote:

Originally Posted by SEHunter

Thanks. I think im going to start over and test one powder at a time. I usually have 2 different loads of about 3 or 4 different powders each time i shoot. Thats too overwhelming to deal with seating depth while trying to pick a powder at the same time. I think i need to get the best combo with each powder then go back and compare the powders.

The chance that you may wear the barrel enough to change its performance characteristics (and thereby change both the pressure and accuracy behaviors) is real. So, you have to pick your variables carefully and keep good records so you can minimize the number of rounds you use for testing.

Good Luck. You can do it.

Happy New Year

Lost Sheep

brickeyee · January 1, 2011, 07:33 PM

Quote:

yesterday, i had a load that was raised a half grain and the velocity was slower than the exact load with a half grain less. I know from load data that i was in the max range.

A smaller velocity increase with a powder increment or no velocity increase is often a sign you have hit maximum.

Quote:

Can it be said that the extra half grain pushed the load out of the average pressure range? Is a drop in velocity with higher charges always a sign of peak pressure?

There is no way to be sure what the actual peak pressure is without measuring equipment (and even then calibration against a standard is a real PITA).

If you get QuickLoad, you can see how the powder burning is very quick, and then the pressure simply falls as the bullet increases the volume the powder gases occupy as the bullet moves down the barrel.

One of the problems with usiong a chronograph without pressure measuring equipment is that you only have insight into the average pressure that drove the bullet down the barrel.

It does not tell you what the peak pressure was.

SEHunter · January 1, 2011, 11:26 PM

All i know to do is read the primers and check for smooth chambering and ejection. I have always heard that primer signs will be seen before pressure gets to the point that the gun will come apart, so i always pay very close attention to each spent round. I usually have a fired factory brass with me to compare to my reloaded brass after shot.

700cdl · January 2, 2011, 11:08 PM

Wow, this topic can get pretty hairy. To do what you are desiring, increase velocity I would first go to an extreme slow burning powder as it will allow for a dense load or even a compressed load. Then seat as close to the lands as possible without touching them. Most rifles have very tapered lands and will tollerate touching bullets without noticable pressure issues. However, if you want to stay clear of extreme pressures don't seat to the lands. Using real slow powders will allow you to seat just off the lands, I seat .002 off in all my high powered rifles and get real high velocity, and as well, great acuracy. Loading like this with the faster burning powders will likely produce a speratic velocity and varying pressures. Just watch how deep you seat more than anything else. Seating deeper than recomended in the data for minimum COAL will drive pressures up drastically at some point, most likely within the first .010" you will see an increase in pressures. Note, the olgive on many bullets is not consistent thus making it almost impossible to consistently seat .002" off the lands without physically checking each round as you seat for distance off lands.

SEHunter · January 3, 2011, 05:54 AM

Sounds good. Thanks. I was previously seated out to just off the lands (.02") and i have moved it back in now. I have the bullet in the case exactly .224", not includeing the base where the taper of the boat tail is. This will probably be my permanent depth. I want the bullet to be held in the case good and this coal which is 2.445" is still longer than the sammi coal of 2.350", i believe it is. Im fairly confident i will find a load that will work with this depth.

cdoc42 · January 3, 2011, 03:23 PM

"yesterday, i had a load that was raised a half grain and the velocity was slower than the exact load with a half grain less. I know from load data that i was in the max range."

I don't think anyone answered this, but I might have missed it. I recall reading some time ago that you can get a velocity reduction like you described but I don't remember the details. Maybe someone else can add to that to explain it.

SEHunter · January 3, 2011, 03:31 PM

Its the first time i have seen it personally. It was only about 15 or 20 fps but it was like that between every round of the two groups.

January 1, 2011, 11:00 AM	#1
SEHunter Senior Member Join Date: October 6, 2009 Posts: 332	Bullet depth vs. powder charge vs. velocity Please bear with me...If you have a random loaded cartridge, does seating the bullet deeper require less charge or allow for a slightly higher charge? I realize the deeper the bullet sits, the less capacity there is but it has also been said that the bullet being at or on the lands increases pressure. Would i have a higher velocity with the same exact charge while the bullet is close to the rifling or set back as deep as say a factory round? I have a couple of accurate shooting loads for my 22-250 but the velocities are slower than factory rounds. I would like to exceed or atleast match those velocities and i havent experimented with bullet seating depth so i just wanted to have this info before i use the same powder charge. Thanks guys.

January 1, 2011, 01:58 PM	#4
Shoney Senior Member Join Date: February 21, 2002 Location: Transplanted from Montana Posts: 2,311	SEHunter A decrease in the case volume, seating the bullet deeper, results in higher pressure. A large capacity case will have less pressure increase, when compared to a small capacity case, if the depth change is identical; i.e. 308 vs 300WM. A bullet set at zero inches off the lands (touching the lands) will have more pressure than a bullet seated at 0.005" off. The farther off the lands up to a point (unknown in each weapon without pressure sensors) the presure will decrease, then start to increase again because of reduction of volume in the case. If you want more velocity with no decrease in accuracy, you will just have to experiment with seating depths of 0.050 to 0.020 off the lands, and an increase in powder charge. Many weapons have the lands so far back, you will not be able to keep one diameter of the bullet in the case neck. You may need to change powders and start the process all over again. The powders used in factory cartridges is usually specifically blended for the factory and is not available to the reloader. __________________ 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

January 1, 2011, 11:26 PM	#8
SEHunter Senior Member Join Date: October 6, 2009 Posts: 332	All i know to do is read the primers and check for smooth chambering and ejection. I have always heard that primer signs will be seen before pressure gets to the point that the gun will come apart, so i always pay very close attention to each spent round. I usually have a fired factory brass with me to compare to my reloaded brass after shot. Last edited by SEHunter; January 2, 2011 at 09:44 AM.

January 3, 2011, 05:54 AM	#10
SEHunter Senior Member Join Date: October 6, 2009 Posts: 332	Sounds good. Thanks. I was previously seated out to just off the lands (.02") and i have moved it back in now. I have the bullet in the case exactly .224", not includeing the base where the taper of the boat tail is. This will probably be my permanent depth. I want the bullet to be held in the case good and this coal which is 2.445" is still longer than the sammi coal of 2.350", i believe it is. Im fairly confident i will find a load that will work with this depth. Last edited by SEHunter; January 3, 2011 at 06:49 AM.

January 1, 2011, 11:08 AM	#2
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	Peak pressure blows up guns, and is directly affected by case volume and distance to the lands. Average pressure drives bullets faster. The problem is keeping peak pressure within safe limits while getting a higher average pressure to increase velocity.

January 1, 2011, 11:32 AM	#3
SEHunter Senior Member Join Date: October 6, 2009 Posts: 332	yesterday, i had a load that was raised a half grain and the velocity was slower than the exact load with a half grain less. I know from load data that i was in the max range. Can it be said that the extra half grain pushed the load out of the average pressure range? Is a drop in velocity with higher charges always a sign of peak pressure?

January 1, 2011, 05:21 PM	#5
SEHunter Senior Member Join Date: October 6, 2009 Posts: 332	Thanks. I think im going to start over and test one powder at a time. I usually have 2 different loads of about 3 or 4 different powders each time i shoot. Thats too overwhelming to deal with seating depth while trying to pick a powder at the same time. I think i need to get the best combo with each powder then go back and compare the powders. Probably is the better way anyway. Thanks again.

January 2, 2011, 11:08 PM	#9
700cdl Senior Member Join Date: December 6, 2010 Posts: 216	Wow, this topic can get pretty hairy. To do what you are desiring, increase velocity I would first go to an extreme slow burning powder as it will allow for a dense load or even a compressed load. Then seat as close to the lands as possible without touching them. Most rifles have very tapered lands and will tollerate touching bullets without noticable pressure issues. However, if you want to stay clear of extreme pressures don't seat to the lands. Using real slow powders will allow you to seat just off the lands, I seat .002 off in all my high powered rifles and get real high velocity, and as well, great acuracy. Loading like this with the faster burning powders will likely produce a speratic velocity and varying pressures. Just watch how deep you seat more than anything else. Seating deeper than recomended in the data for minimum COAL will drive pressures up drastically at some point, most likely within the first .010" you will see an increase in pressures. Note, the olgive on many bullets is not consistent thus making it almost impossible to consistently seat .002" off the lands without physically checking each round as you seat for distance off lands.

January 3, 2011, 03:23 PM	#11
cdoc42 Senior Member Join Date: March 13, 2005 Location: Pennsylvania Posts: 1,687	"yesterday, i had a load that was raised a half grain and the velocity was slower than the exact load with a half grain less. I know from load data that i was in the max range." I don't think anyone answered this, but I might have missed it. I recall reading some time ago that you can get a velocity reduction like you described but I don't remember the details. Maybe someone else can add to that to explain it.

January 3, 2011, 03:31 PM	#12
SEHunter Senior Member Join Date: October 6, 2009 Posts: 332	Its the first time i have seen it personally. It was only about 15 or 20 fps but it was like that between every round of the two groups.