Why do I need so much powder?

[Dean2]

You have multiple variables at work;
Changed powder lots
Barrel has 300 rounds fired or 50% used
You are using different Chronographs
Air Temp changes
Humidity changes
Virgin brass to 3x fired
Varying neck tension due to work hardening
It isn't real clear from your posts as to the seating depths being the same. If you are seating them further out to maintain relationship to lands, you are increasing case capacity, and dropping pressure.
Have you tested the scale and are you using the same scale.

With this many factors, and the potential that a number of them are in play at the same time, I have no problem seeing a 100 fps velocity change. What is a little surprising is that it takes almost 2.5 - 4 grains to pick up 100 fps. Min to max published loads are only 4 to 5 grains apart and are over 200 fps different in that increase. You are running 169 Hammers at 3300 fps and 180 Bergers at almost 3200 fps, so I would say you have passed max load. I think you may be at the load point where velocity has plateaued and adding more powder does not increase velocity by any significant amount. That is usually a very clear sign that you should back off at least a couple of grains and call it good.

This is Berger's Load data for their 175 grain bullets. You are almost 5 grains PAST suggested max load with the 180s alone, and almost 100 fps faster than the Berger 175 loads..

28 Nosler
175 Grain
Barrel Length = 26"
COAL = 3.417"
Optimal performance may be achieved in your rifle
at a different COAL. Read HERE for details.
175 gr Elite hunter
G1 BC = 0.656 G7 BC = 0.336
Part # 28554 - 1 in 9" twist or faster
For bullet dimensional details, click HERE.
warning - Approach maximum loads with caution as all rifles and
reloading techniques will be different.
Additional safety information can be found HERE.
Powder Start
Load
Approx.
Start Vel.
Max
Load
Approx.
Max Vel.
Approx.
Fill Ratio
IMR 7828 69.0 2888 72.8 3035 94%
AA Magpro 72.5 2892 76.4 3043 90%
RETUMBO 77.0 2911 81.3 3066 101%
NORMA 217 77.0 2906 81.3 3066 103%
VIHT N570 78.0 2936 82.3 3114 98%
RE-33 82.0 2927 86.3 3103 100%
We recommend using G7 BC to achieve the most
accurate trajectory prediction.

 

[kfreeze]

Sounds like it may be part barrel wear, but mostly changing the powder by mixing it. The n570 lot that I use in my 28 seems to run 5 grns less than others to get the same velocities. Long throated chamber and 29" barrel 78.0 grns gives me 3140 fps.

 

[Huntnful]

Sounds like it may be part barrel wear, but mostly changing the powder by mixing it. The n570 lot that I use in my 28 seems to run 5 grns less than others to get the same velocities. Long throated chamber and 29" barrel 78.0 grns gives me 3140 fps.

I'm definitely going to test out a fresh powder lot. But I mean this new jug gives me great ES & SD's so I'm not stressing about it. Got about 5lbs left in the new jug. Probably just run through it and then see if a new lot makes a difference.

 

[Huntnful]

You have multiple variables at work;
Changed powder lots
Barrel has 300 rounds fired or 50% used
You are using different Chronographs
Air Temp changes
Humidity changes
Virgin brass to 3x fired
Varying neck tension due to work hardening
It isn't real clear from your posts as to the seating depths being the same. If you are seating them further out to maintain relationship to lands, you are increasing case capacity, and dropping pressure.
Have you tested the scale and are you using the same scale.

With this many factors, and the potential that a number of them are in play at the same time, I have no problem seeing a 100 fps velocity change. What is a little surprising is that it takes almost 2.5 - 4 grains to pick up 100 fps. Min to max published loads are only 4 to 5 grains apart and are over 200 fps different in that increase. You are running 169 Hammers at 3300 fps and 180 Bergers at almost 3200 fps, so I would say you have passed max load. I think you may be at the load point where velocity has plateaued and adding more powder does not increase velocity by any significant amount. That is usually a very clear sign that you should back off at least a couple of grains and call it good.

This is Berger's Load data for their 175 grain bullets. You are almost 5 grains PAST suggested max load with the 180s alone, and almost 100 fps faster than the Berger 175 loads..

28 Nosler
175 Grain
Barrel Length = 26"
COAL = 3.417"
Optimal performance may be achieved in your rifle
at a different COAL. Read HERE for details.
175 gr Elite hunter
G1 BC = 0.656 G7 BC = 0.336
Part # 28554 - 1 in 9" twist or faster
For bullet dimensional details, click HERE.
warning - Approach maximum loads with caution as all rifles and
reloading techniques will be different.
Additional safety information can be found HERE.
Powder Start
Load
Approx.
Start Vel.
Max
Load
Approx.
Max Vel.
Approx.
Fill Ratio
IMR 7828 69.0 2888 72.8 3035 94%
AA Magpro 72.5 2892 76.4 3043 90%
RETUMBO 77.0 2911 81.3 3066 101%
NORMA 217 77.0 2906 81.3 3066 103%
VIHT N570 78.0 2936 82.3 3114 98%
RE-33 82.0 2927 86.3 3103 100%
We recommend using G7 BC to achieve the most
accurate trajectory prediction.

Great info! I'm also running a COAL of 3.8" about.

 

[Huntnful]

You have multiple variables at work;
Changed powder lots
Barrel has 300 rounds fired or 50% used
You are using different Chronographs
Air Temp changes
Humidity changes
Virgin brass to 3x fired
Varying neck tension due to work hardening
It isn't real clear from your posts as to the seating depths being the same. If you are seating them further out to maintain relationship to lands, you are increasing case capacity, and dropping pressure.
Have you tested the scale and are you using the same scale.

With this many factors, and the potential that a number of them are in play at the same time, I have no problem seeing a 100 fps velocity change. What is a little surprising is that it takes almost 2.5 - 4 grains to pick up 100 fps. Min to max published loads are only 4 to 5 grains apart and are over 200 fps different in that increase. You are running 169 Hammers at 3300 fps and 180 Bergers at almost 3200 fps, so I would say you have passed max load. I think you may be at the load point where velocity has plateaued and adding more powder does not increase velocity by any significant amount. That is usually a very clear sign that you should back off at least a couple of grains and call it good.

This is Berger's Load data for their 175 grain bullets. You are almost 5 grains PAST suggested max load with the 180s alone, and almost 100 fps faster than the Berger 175 loads..

28 Nosler
175 Grain
Barrel Length = 26"
COAL = 3.417"
Optimal performance may be achieved in your rifle
at a different COAL. Read HERE for details.
175 gr Elite hunter
G1 BC = 0.656 G7 BC = 0.336
Part # 28554 - 1 in 9" twist or faster
For bullet dimensional details, click HERE.
warning - Approach maximum loads with caution as all rifles and
reloading techniques will be different.
Additional safety information can be found HERE.
Powder Start
Load
Approx.
Start Vel.
Max
Load
Approx.
Max Vel.
Approx.
Fill Ratio
IMR 7828 69.0 2888 72.8 3035 94%
AA Magpro 72.5 2892 76.4 3043 90%
RETUMBO 77.0 2911 81.3 3066 101%
NORMA 217 77.0 2906 81.3 3066 103%
VIHT N570 78.0 2936 82.3 3114 98%
RE-33 82.0 2927 86.3 3103 100%
We recommend using G7 BC to achieve the most
accurate trajectory prediction.

Also I should clarify that it doesn't take me 4-5 grains to gain 100FPS at all. I gain 50FPS per grain about. For instance my recent load development went



86. 3100
87. 3150
87.5 3185FPS

 

[kfreeze]

I'm definitely going to test out a fresh powder lot. But I mean this new jug gives me great ES & SD's so I'm not stressing about it. Got about 5lbs left in the new jug. Probably just run through it and then see if a new lot makes a difference.

Usually if you matxh your velocity it still works the same.

 

[Lenny Foffa]

Sorry to ask, but how did you measure the throat and determine that you had.01 throat erosion. How is that done?? What instrument did you use?? I would really like to know. Thank You, Lenny

 

[Lefty7mmstw]

Since I have not seen this put out, here is what I am pretty sure is part of the answer.
new barrels are rougher unless they are hand lapped from the factory. if you have 100 FPS faster and take a bit more powder to give the same pressure and velocity then your barrel has burnished in and is slicker than it came from the factory. I learned this from my own experience. once my barrels were bunished (shot in) they had lower pressure, lower velocities, and took a bit more powder to bring them back to what I was used to. this could be part or most of your answer.

That would make sense if it's the case. I mean every round for the last 200 rounds just takes more powder than the 1st hundred. Still shoots excellent and super easy to develop a load for.

>>>>

My experience is the opposite. As the barrel breaks in, it speeds up - and less powder is required.

Most of the time they will speed up... usually it takes serious throat erosion or a different lot (slower) of powder to cause slowdown.